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Omeprazole Side Effects & Adverse Reactions (List)

Omeprazole is a medication prescribed for the treatment of gastroesophageal reflux disease (GERD); peptic ulcer disease; erosive esophagitis; eosinophilic esophagitis; Zollinger-Ellilson syndrome; and medical conditions associated with gastric acid hypersecretion.  In some cases, omeprazole may also be utilized for the prophylaxis of upper gastrointestinal bleeding (in at-risk populations) and as an adjunct treatment for H. plyori infection.

Historical reports suggest that omeprazole was first synthesized in the 1970s by chemists employed with the pharmaceutical company “Astra.”  After successful clinical trials, omeprazole received approval in 1988 for use throughout Europe under the trade name “Losec” – and in 1990 for use in the United States under the trade name “Prilosec.”

Though many individuals with gastrointestinal disorders derive noticeable benefit from the ongoing administration of omeprazole, the medication can sometimes cause unwanted side effects.  For this reason, if you’re using omeprazole, it’s probably a good idea to familiarize yourself with potential side effects and adverse reactions that could emerge during treatment.

Omeprazole Side Effects (Most Common Reactions)

Included below is a list of common side effects associated with omeprazole treatment.  Despite the fact that some omeprazole side effects are notoriously more common than others, side effects are also subject to significant interindividual variation among omeprazole users.  In other words, the specific side effects that you experience (as well their severities) might be markedly different than the side effects reported by another user.

Nevertheless, clinical data indicate that the most common omeprazole side effects include: headache, nausea, vomiting, diarrhea, stomach pain, flatulence, and constipation.  Side effects of omeprazole are described below in greater detail.  If you have a question about the side effects that you’re experiencing, contact a medical doctor.

Diarrhea: Some sources suggest that diarrhea is the most common side effect of omeprazole treatment, occurring in up to 14% of users.  If you’re experiencing diarrhea, it is important to realize that ongoing diarrhea may: interfere with nutrient absorption, cause dehydration, and/or induce unwanted weight loss.  In the event that your omeprazole-induced diarrhea becomes severe, ask your doctor about trying an antidiarrheal agent (e.g. Imodium).

It is believed that the side effect of diarrhea occurs mostly as a result of reduced generation of stomach acid.  When stomach acidity significantly decreases, it becomes increasingly difficult for the gastrointestinal tract to absorb and digest certain foods.  As a result, food may move through the digestive tract rapidly, leaving omeprazole users with frequent and/or loose stools.

Headache: According to a review of omeprazole trials, one of the most common side effects resulting from treatment is headache.  It is estimated that 7% of omeprazole users will end up with headache as a side effect of the medication.  It isn’t fully understood what causes headaches as a side effect, but some patients speculate that things like: anxiety, gut bacteria changes, and/or vitamin deficiencies could be culpable.

Furthermore, it is thought that the higher the dose of omeprazole that’s administered, the greater the likelihood that headaches will occur.  In most cases, headaches will be transient (“off and on”) and shouldn’t be severe enough to warrant omeprazole discontinuation.  If you’re experiencing headaches as a side effect – ask your doctor about using a headache relief medication, get your vitamin levels checked, and stay properly hydrated.

Nausea: Medical literature suggests that around 4% of omeprazole users will experience nausea as a side effect.  For certain users, nausea might emerge as a side effect in the early stages of treatment – and eventually fade as the body becomes better-adapted to omeprazole’s action and regular presence.  For others, nausea may remain severe throughout treatment and lead to vomiting.

If the nausea you experience while using omeprazole is intense enough to trigger vomiting, you should report this to your doctor as soon as possible.  Though there may be some ways in which you can decrease the side effect of nausea (such as by using an antiemetic), nausea might just be a sign that your body won’t tolerate omeprazole.  Some speculate that nausea could stem from omeprazole-mediated changes in stomach acid and food digestion.

Vomiting: Another one of the most common side effects of omeprazole is vomiting.  Research suggests that approximately 3% of omeprazole users will experience vomiting as a treatment-related side effect.  In most cases, vomiting reactions are preceded by intense or unremitting nausea and food intake.

In the event that you experience vomiting while using omeprazole, report this reaction to your medical doctor immediately – as it could signify a severe adverse reaction.  If the vomiting isn’t caused by a severe adverse reaction, it could’ve been provoked by: the consumption of specific foods, the consumption of too much food, and/or using too large of an omeprazole dose.  Taking an antiemetic agent along with omeprazole may help some users manage nausea and vomiting throughout treatment.

Flatulence (Gas): It is estimated that 3% of individuals taking omeprazole will experience flatulence or “gas” as a side effect of treatment.  If you notice yourself gassing excessively while taking omeprazole, it’s probably related to changes in digestive function – as a result of decreased stomach acidity.  Your gastrointestinal tract may have a tougher time processing certain foods – which may lead to flatulence, upset stomach, and/or diarrhea.

In most cases, the side effect of flatulence will not be debilitating enough to warrant treatment cessation.  Nevertheless, you may want to monitor your diet and evaluate whether certain foods are more likely to cause flatulence (while using omeprazole) than others.  If you can identify and decrease intake of flatulence-inducing foods, you may be able to minimize this side effect.

Stomach pain (Abdominal): Stomach pain, particularly within the abdominal region, is thought to occur as a side effect of omeprazole in 1% to 5% of users.  There are many potential reasons that stomach pain might occur while using omeprazole, the most obvious being: decreased stomach acidity.  When stomach acid is significantly reduced, some individuals may experience major changes in food absorption and digestion.

Changes in food absorption and digestion may lead to gas production, diarrhea, indigestion, bloating, and/or constipation – each of which might be implicated in causing stomach pain.  If you’re experiencing stomach aches while taking omeprazole, it may help to make dietary adjustments and/or increase water intake.  That said, if omeprazole is suboptimally effective in managing your gastrointestinal condition, the stomach pain that you’re experiencing could be directly attributable to high gastric acid levels (rather than the omeprazole).

Constipation: It is estimated that between 1% and 5% of persons taking omeprazole will experience constipation, or difficulty emptying the bowels during treatment.  Constipation may be accompanied by stomach aches, flatulence, indigestion, and hardening of stools.  If you experience constipation as a side effect of omeprazole, it may prove helpful to modify your diet (consuming more fibrous foods) and/or drink more water.

Furthermore, it may help to engage in more physical exercise (e.g. walking or jogging) – as this might help reverse the constipation.  Always ask your doctor what he/she thinks would be safest and/or best for the management of constipation as an omeprazole side effect.  There may be adjunct substances (e.g. laxatives) that would help negate constipation as a side effect of omeprazole.

Dizziness: Dizziness is a side effect that occurs in approximately 2% of persons using omeprazole.  It is unclear as to whether the side effect of dizziness is directly caused by omeprazole – or whether it could be a downstream reaction stemming from a more common side effect like diarrhea, nausea, and/or vomiting.  In other words, if you end up vomiting while taking omeprazole, the vomiting could be the specific cause of your dizziness.

Other possible causes of dizziness while using omeprazole include: changes in blood pressure, weight loss, dehydration, imbalanced electrolytes, and/or inadequate vitamin absorption.  If you experience extreme dizziness while taking omeprazole, it is recommended to inform your doctor and work with him/her to identify all prospective causes.  Dizziness and lightheadedness are more likely to occur in the elderly and among persons with preexisting illnesses.

Acid regurgitation: Acid regurgitation or “acid reflux” is sometimes documented as being a side effect of omeprazole.  However, because omeprazole generally inhibits stomach acid production, it’s unlikely that acid regurgitation is caused by the medication.  What’s more likely is that omeprazole isn’t sufficiently reducing stomach acid production, and a person’s preexisting medical condition (e.g. GERD) remains inadequately treated – leading to the regurgitation of stomach acid.

Any acid regurgitation that you experience during treatment might be accompanied by: burning pain in the lower chest (i.e. heartburn) and/or burping.  If the acid regurgitation doesn’t seem to improve with omeprazole administration, you may need to ask your doctor about increasing your omeprazole dose.  If dosage adjustments don’t seem to suppress the acid regurgitation, you may need to discontinue omeprazole and switch to a different medication.

Weight loss or gain: A side effect of omeprazole that some individuals may experience is weight change.  Acute weight change, such as in the early stages of treatment, might be related to various side effects such as: diarrhea, nausea, and/or vomiting.  For example, if you have uncontrollable diarrhea or vomiting, your body may eliminate many of the calories that you consume before they are properly absorbed and stored as fat.

Diarrhea and vomiting can also cause individuals to lose “water weight” by dehydrating the body.  Furthermore, if you’re constantly nauseous, this could interfere with your appetite – causing you to consume fewer calories than usual, ultimately yielding weight loss.  That said, research indicates that long-term omeprazole administration in humans is associated with bodyweight gain among patients with gastroesophageal reflux disorder, likely by modulating gut bacteria, hormones, and peptides that influence appetite.

Burping: A relatively common symptom of GERD (gastroesophageal reflux disease) and other stomach acid hypersecretory conditions is frequent burping – or belching.  It is believed that burping occurs due to a combination of stomach acid rising within the gastrointestinal tract and increased generation of gas.  Essentially when the stomach acid and/or gas rises to the upper gastrointestinal tract area – it provokes a burping or belching response.

Most individuals who use omeprazole should actually notice a decrease in burping throughout treatment (compared to pre-treatment).  If you end up burping more frequently while taking omeprazole than you did before treatment, it’s possible that the medication isn’t effectively reducing your stomach acid production.  Perhaps a dosage adjustment, longer duration of treatment, and/or medication change might be needed to counteract the burps.

Bloating: A small percentage of omeprazole users may experience bloating as a side effect such that they feel swollen with fluid and/or gas.  The side effect of bloating is probably attributable to omeprazole-mediated changes throughout the digestive tract, leading to increased water retention, gas production, constipation, and/or indigestion.  For certain individuals, it may be possible to reduce or completely counteract the side effect of bloating via dietary modifications (e.g. reducing calorie intake) and/or drinking more water.

That said, bloating might also result from omeprazole-mediated changes in gut bacteria, leading to dysbiosis and bacterial overgrowth.  Moreover, facial bloating could be the sign of a severe adverse reaction to omeprazole – especially if accompanied by swelling, dizziness, and a rash.  If you experience severe bloating, particularly in the facial region, report this to a medical doctor.

Injection site reactions: In the United Kingdom, omeprazole is manufactured in an injectable format.  If you’re using an injectable form of omeprazole, you may experience “injection site reactions” – such as: swelling, pain, redness, itchiness, discoloration, and/or bruising at the specific site or location in which omeprazole was injected.  For a majority of individuals, injection site reactions should gradually heal within a few days or weeks (depending on the severity).

However, if an injection site reaction doesn’t appear to heal and/or worsens in appearance (e.g. swelling or redness increases) – seek immediate medical attention.  Worsening of an injection site reaction may be the sign of an infection and/or a severe adverse reaction.  Managing any bleeding and applying ice may prove helpful for decreasing the severity of an injection site reaction.  (If you frequently experience injection site reactions, you may want to transition from intravenous (IV) omeprazole to an oral format).

Omeprazole Adverse Effects & Reactions (List)

Below is a list of rare adverse effects and reactions associated with omeprazole.  Understand that these adverse effects are reported as occurring in less than 2% of omeprazole users, making them extremely uncommon.  However, because adverse reactions can be life-threatening, anyone who experiences an adverse reaction should seek emergency medical attention.  If you’re using omeprazole, it may be smart to read through and get a basic understanding of these adverse reactions, so that if one occurs, you’ll be able to identify and report it to a medical doctor.

  • Acute interstitial nephritis: An adverse reaction to omeprazole and other proton pump inhibitors that’s been documented in medical literature is acute interstitial nephritis. Acute interstitial nephritis refers to swelling or inflammation of the kidneys.  If left untreated, acute interstitial nephritis can lead to renal failure.  Signs of acute interstitial nephritis include: blood in urine, fever, altered urinary output, rash, nausea, vomiting, and confusion.
  • Allergic reaction: A tiny percentage of omeprazole users may experience an allergic reaction to the medication. Possible signs of an allergic reaction to omeprazole are: breathing difficulty (or shortness of breath); swollen body parts (face, tongue, throat, etc.); skin rash; itchiness; watery eyes; mental confusion; kidney dysfunction; lightheadedness; and behavioral changes.  If you or someone you know exhibits the signs of an allergic reaction to omeprazole – emergency medical care is necessary.
  • Anxiety: Although omeprazole doesn’t directly act within the central nervous system, it’s understood that omeprazole can modulate levels of hormones, peptides, and gut bacteria in the peripheral. Because the peripheral nervous system interacts with the central nervous system, the omeprazole-mediated peripheral changes might alter neurochemistry of a user to provoke the side effect of anxiety.  There are many anecdotal accounts from omeprazole users suggesting that this medication (and other proton-pump inhibitors) cause anxiety as a side effect.
  • Back pain: In clinical trials of omeprazole, 1.1% of users reported back pain as an adverse reaction. It is unclear exactly why back pain might occur as a side effect of omeprazole, but vitamin deficiencies, bone loss, and/or muscle loss could be potential reasons.  If the back pain you experience becomes intense – and is directly attributable to omeprazole, discuss it with your doctor.
  • Benign fundic gland polyps: Long-term administration of omeprazole (and other proton pump inhibitors) is linked to the development of benign fundic gland polyps, or abnormal tissue growths throughout the stomach. Although benign fundic gland polyps are not likely to cause cancer, they may be disconcerting to the patient.  In most cases, benign fundic gland polyps will resolve naturally following the discontinuation of omeprazole and other proton pump inhibitors.
  • Dry mouth: Despite the fact that the probability of experiencing dry mouth as a reaction to omeprazole is very low, this is an adverse reaction that some users have documented.  Dry mouth might result from omeprazole altering activity of the salivary glands, ultimately decreasing saliva secretion.  It’s also possible that dry mouth as a reaction to omeprazole might stem from medication-related alterations in oral bacteria.
  • Fever: Pyrexia or “fever” can occur as an adverse reaction to omeprazole treatment. Data indicate that fever is significantly more likely to occur in very young children taking omeprazole – compared to adults.  Nevertheless, if you develop a fever while using omeprazole, do not hesitate to report it to your doctor – as this could be the sign of an allergic reaction, bacterial infection, or life-threatening reaction.
  • Flu-like symptoms: A small percentage of individuals will report flu-like symptoms while taking omeprazole. Perhaps the combination of common side effects such as: diarrhea, nausea, and/or vomiting, coupled with other reactions such as muscle weakness and/or fever, leads some to feel like they have the flu.  Flu-like symptoms are reported as occurring at an incidence rate of 1%.
  • Hair loss: Some omeprazole users claim that the medication causes hair thinning or hair loss. Though there’s not any significant medical literature to substantiate the idea that omeprazole causes hair loss, it’s reasonable to consider that hair loss might occur during treatment due to impaired vitamin absorption and a vitamin deficiency.  In the event that omeprazole is culpable for your hair loss, discontinuation should result in hair regrowth.
  • Hematologic complications: A subset of individuals taking omeprazole may develop hematologic complications such as: leukopenia (low white blood cells); thrombocytopenia (low thrombocytes); pancytopenia (deficiency in red cells, white cells, and platelets); and/or agranulocytosis (low white blood cell or neutrophil count). It is recommended to receive regular blood work during treatment to detect any potential omeprazole-induced blood cell abnormalities.
  • Hepatic encephalopathy: Hepatic encephalopathy is a condition characterized by loss of brain function due to an inadequate removal of toxins from the bloodstream by the liver. Signs of hepatic encephalopathy include: confusion, malodorous breath, shaking of hands and arms, and disorganized speech.  In rare cases, hepatic encephalopathy can occur as a result of using proton pump inhibitors like omeprazole – usually in persons with preexisting liver impairment.
  • Hepatic impairment: If you have normal liver function prior to using omeprazole, it’s unlikely that omeprazole will cause hepatic impairment as a side effect. However, hepatic impairment and failure have been reported as rare adverse reactions among persons with preexisting liver conditions (e.g. cirrhosis).  If you have a history of hepatic impairment before using omeprazole, have your liver checked regularly throughout treatment to ensure that your liver function doesn’t worsen from the medication.
  • Immune dysfunction: Administration of omeprazole may provoke immune dysfunction in certain users as an adverse reaction. If immune dysfunction occurs as a result of omeprazole administration, this could increase risk of serious infection.  Signs of immune dysfunction during treatment include: frequent infections, anaphylaxis, and systemic lupus erythematosus.
  • Indigestion: Indigestion, also known as dyspepsia, can occur as a side effect of omeprazole. Omeprazole may alter function of the digestive tract, which could trigger indigestion in a subset of users.  Signs of indigestion include: stomach fullness, bloating, flatulence, heartburn, nausea, and burping.  In some cases, indigestion may be a byproduct of constipation (among those who become constipated from the medication).
  • Infection: It is known that using omeprazole can increase one’s risk of developing specific types of infections, largely as a result of its effect on stomach acid. Because omeprazole reduces the production of stomach acid, pathogenic bacteria have an easier time surviving within the gastrointestinal tract.  If pathogenic bacteria survive and proliferate while taking omeprazole, this could lead to the development of a bacterial infection.  Clostridium difficile is one of the most common bacterial infections documented in omeprazole users.
  • Insomnia: Most research suggests that omeprazole can help treat insomnia among persons with gastroesophageal reflux disease (GERD). This is likely due to the fact that excessive acid reflux can make it difficult to fall asleep – and provoke frequent nighttime awakenings.  That said, clinical trial data indicate that a small percentage of individuals will experience insomnia as a side effect of omeprazole treatment.
  • Itchiness: On occasion, omeprazole might trigger a rash accompanied by itchiness. If you become itchy while using omeprazole, this could be the sign of an allergic reaction (and secretion of histamine), dermatologic reaction (e.g. Stevens-Johnson syndrome), or a bacterial infection.  It is recommended to always report itchiness to a medical doctor as soon as it is noticed.
  • Memory loss & dementia: It isn’t fully known as to whether omeprazole (and other proton pump inhibitors) cause memory loss and dementia. Nevertheless, there is strong associational research suggesting that proton pump inhibitors significantly increase dementia risk (by up to 50%).  Researchers speculate that drugs like omeprazole might interfere with the degradation and clearance of amyloid beta peptide, and cause vitamin B12 deficiency – leading to accelerated neurodegeneration and/or cognitive impairment.
  • Metabolic abnormalities: High cholesterol, elevated triglycerides, elevated liver enzymes (e.g. AST/ALT), and elevated creatine kinase (CK) could be signs of metabolic dysfunction. If you have a history of metabolic abnormalities and/or a preexisting metabolic condition, it is recommended to receive regular metabolic evaluations (from a medical doctor) while using omeprazole to ensure that the medication isn’t causing metabolic dysfunction.
  • Muscle cramps, pain, weakness, twitching: Some omeprazole users have reported a combination of muscle cramps; pains or aches; weakness; and twitching – throughout treatment. If you’re experiencing muscle cramps, pain, weakness, or twitching – these reactions could be related to vitamin deficits (e.g. magnesium); electrolyte imbalances; and/or dehydration.  That said, because omeprazole can sometimes cause osteoporosis and bone loss, a loss of bone density might also account for muscle pain and/or weakness.
  • Osteoporosis & bone fractures: Use of omeprazole has been associated with increased risk of developing osteoporosis and bone fractures. Research of omeprazole in animal models suggests that long-term treatment may decrease bone mineral density.  It is thought that development of osteoporosis and bone fractures while using omeprazole might be attributable to impaired vitamin absorption and corresponding vitamin deficiencies.
  • Pharyngitis: Approximately 1% of omeprazole users will experience pharyngitis as an adverse effect of treatment. Pharyngitis is defined as swelling in the back of the throat (pharynx) between the tonsils and voice box.  Pharyngitis could be the sign of an allergic reaction to omeprazole or attributable to bacterial overgrowth in the throat area (possibly resulting from omeprazole treatment).
  • Photosensitivity: Photosensitivity is a condition associated with a pronounced skin rash, sunburn, and/or blistering. Although extremely rare, it is estimated that between 0.1% and 1% of omeprazole users develop photosensitivity as a result of treatment.  In the event that you experience photosensitivity from omeprazole – avoid sun exposure and seek medical help.
  • Potentially-fatal skin reactions: It is important to be cognizant of any skin rash and/or discoloration that results from omeprazole use. Although extremely rare, some individuals may develop potentially-fatal skin conditions such as: toxic epidermal necrolysis, angioedema, cutaneous lupus erythematosus, erythema multiforme, and Stevens-Johnson syndrome – while using omeprazole.  Contact a medical professional immediately if you develop hives, skin discoloration, and/or itchiness when taking omeprazole.
  • Psychiatric symptoms: Two of the most common psychiatric symptoms that occur while using omeprazole (and proton pump inhibitors) include anxiety and insomnia. That said, research suggests that up to 0.1% of users might also experience depression, agitation, aggression, hallucinations, or apathy as adverse reactions.  Persons with preexisting psychiatric conditions and/or with vitamin deficiencies may be at highest risk of experiencing psychiatric symptoms while using omeprazole.
  • Rhinitis: Rhinitis can occur in up to 2% of omeprazole users as an adverse reaction. Persons who develop rhinitis will present with irritation and swelling of the mucous membrane in the nose.  This may cause symptoms such as runny nose and nasal congestion.  Rhinitis may occur along with pharyngitis – and could be the sign of an upper respiratory tract infection.
  • Skin rash: It is estimated that around 2% of omeprazole users will develop a skin rash as a result of the medication. A skin rash may be localized (within one particular region) or widespread (throughout the body).  Rashes might also be itchy, red, and accompanied by swelling.  If you develop a skin rash from treatment, seek emergency medical attention – as this could be the sign of a life-threatening dermatological reaction like: Stevens-Johnson Syndrome (SJS) or toxic epidermal necrolysis (TEN).
  • Taste changes: When omeprazole is administered as a standalone agent, taste changes are relatively uncommon. However, when omeprazole is administered as part of a combination therapy (with clarithromycin), taste perversion is one of the most common side effects – occurring in around 15% of users.  Taste perversion or dysgeusia may be described as lack of taste (ageusia) or reduced taste sensitivity (hypogeusia).  Some individuals may notice alterations in the perception of smell and tongue discoloration along with irregular taste.
  • Tongue discoloration: Tongue discoloration, especially if accompanied by swelling, may be the sign of a serious allergic reaction to omeprazole. Although tongue discoloration is unlikely to occur when using omeprazole as a standalone treatment, it occurs in about 2% of persons who administer omeprazole along with clarithromycin.  It is believed that tongue discoloration is due to altered oral microbial growth.  Colors of discoloration reported in the literature include: yellow, orange, red, black, and white.
  • Upper respiratory tract infection: An upper respiratory tract infection is characterized by the presentation of: scratchy throat, sore throat, sneezing, coughing, and/or nasal congestion. Data from omeprazole trials indicate that nearly 2% of users develop an upper respiratory tract infection during treatment.  Deficiencies in certain vitamins and/or bacterial overgrowth may increase the risk of upper respiratory tract infection while using omeprazole.
  • Vitamin & mineral deficiencies: Vitamin and mineral deficiencies have been reported among persons using omeprazole. The most common vitamin deficiency reported among omeprazole users is magnesium deficiency (or hypomagnesemia).  That said, other relatively common deficiencies resulting from the use of proton pump inhibitors include: vitamin B12, vitamin C, calcium, iron, and sodium.  Be sure to receive regular blood work while taking omeprazole to ensure that you don’t develop a vitamin deficiency.

Note: The above lists of omeprazole side effects and adverse reactions, respectively, might be incomplete.  If you know of additional side effects or adverse reactions associated with omeprazole that weren’t reported, document them in the comments (preferably with a credible medical source to validate the information).

Variables that influence Omeprazole side effects

There are many variables that could influence the side effects and/or adverse reactions that a person experiences while taking omeprazole.  Variables that likely influence the specific side effects that occur while taking omeprazole (and the severities of those side effects) include: dosage of omeprazole; duration of omeprazole use; concurrent substance use; and user-specific factors (e.g. medical status, genetics, lifestyle).

  1. Omeprazole dose (20 mg to 360 mg)

The exact dose of omeprazole that you use on a daily basis might impact whether you experience certain side effects, as well as the severities of the side effects that you experience.  In most cases, it is believed that the greater the dose of omeprazole administered, the more significantly the medication will suppress stomach acid production via blockade of the H+/K+-ATPase enzyme.

Because larger doses of omeprazole modulate physiology of the user to a greater extent than smaller doses, side effects tend to be more prevalent and intense among high-dose users.  On the other hand, because smaller doses of omeprazole won’t alter physiology as significantly, side effects are less likely to occur – and if they do occur – they might be less severe than at high doses.

Medical documentation suggests that omeprazole is typically administered at doses between 20 mg and 40 mg per day in adults with gastroesophageal conditions.  Assuming you’re using a low or standard dose of omeprazole (20 mg to 40 mg per day), the likelihood that you’ll experience unbearable side effects is very low.

That said, some patients may require up to 360 mg of omeprazole per day to manage medical symptoms.  If you’re taking very high doses of omeprazole, you’ll be more likely to end up with intense side effects and harsh adverse reactions due to a larger quantity of the medication modulating physiologic processes (e.g. stomach acid production, nutrient absorption, gut bacteria concentrations, etc.).

  1. Omeprazole treatment duration

The cumulative duration over which a person has consistently administered omeprazole to treat medical symptoms – may influence side effect risk and/or severity.  If you’re a new omeprazole user who recently initiated treatment, there’s a chance that some of the side effects you’re experiencing are attributable to inadequate physiologic adaptation to the medication.

More specifically, because a new user’s body hasn’t fully adapted itself to omeprazole’s regular presence and action, side effects occur.  A subset of new users may find that side effects experienced early in treatment eventually diminish with longer-term use – once their physiology becomes better adapted to omeprazole.

However, there’s evidence indicating that long-term administration of omeprazole (and other proton pump inhibitors) can increase risk of adverse reactions (e.g. osteoporosis, bone fractures, dementia, and vitamin deficiencies).  If you’re a long-term user, you should understand that the extended duration of treatment may be modifying your physiology in ways that provoke new side effects or exacerbate preexisting ones.

  1. Concurrent substance use (Interactions)

If you’re using substances with omeprazole, it is important to consider that concurrently administered agents might: interfere with the action of omeprazole; induce interaction effects; exacerbate omeprazole side effects (via synergistic mechanisms); or trigger side effects that have nothing to do with omeprazole (yet that you might mistakenly attribute to omeprazole).

For example, when omeprazole is administered along with clarithromycin and amoxicillin (as part of “triple therapy”) to treat H. pylori infection, risk of side effects like taste perversion and tongue discoloration significantly increase (compared to omeprazole monotherapy).  The increase in side effect risk among persons using omeprazole as part of triple therapy is probably due to synergistic physiologic actions simultaneously exerted by the trio.

The most significant major drug interaction with omeprazole is clopiodgrel.  Because omeprazole inhibits enzymes CYP2C19 and CYP3A4, and clopidogrel requires these enzymes for its metabolism, patients using clopidogrel may not receive therapeutic quantities of clopidogrel metabolites necessary to reduce the risk of cerebrovascular events like heart attack and stroke, possibly leading to cerebrovascular complications.

Other substances might also interact with omeprazole pharmacokinetically via CYP450 enzymes (e.g. CYP3A4, CYP2C19, CYP2D6), leading to increased or decreased efficacy.  For example, omeprazole’s inhibition of CYP3A4 might substantially increase concentrations of benzodiazepines (most of which are metabolized by this enzyme), leading to more potent benzodiazepine effects (and side effects).

If you’re using medications that require CYP450 metabolism, you may be at increased risk of pharmacokinetically-mediated interaction effects.  Additionally, concurrent use of medications that require stomach acid for absorption (e.g. ketoconazole) might not work as well.  Oppoistely, acid-labile medications (e.g. erythromycin) might be absorbed more extensively when used with omeprazole – leading to more significant effects (and side effects).

Have a medical doctor evaluate the concurrent medications that you’re using with omeprazole to ensure that you don’t experience pharmacokinetically-mediated interactions and/or synergistic side effects.  Moreover, understand that some concurrently-administered substances may cause side effects that you’re wrongfully assuming are from omeprazole – or side effects that overlap with and exacerbate the side effects of omeprazole.

  1. Omeprazole user (specific factors)

There are often user-specific factors that influence the prevalence and/or severities of side effects associated with omeprazole.  User-specific factors that might impact omeprazole side effects include: administration specifics; age; body size; drug format; genetics; lifestyle; and medical conditions.  These user-specific factors probably explain why 2 individuals taking the same dose of omeprazole – for the same duration – may end up with noticeably different side effects.

  • Administration: Details associated with omeprazole administration might account for side effects and/or omeprazole’s efficacy. Omeprazole is most frequently administered in the morning, approximately 1 hour before a meal.  Nevertheless, the specific time of day at which you take omeprazole; whether you take omeprazole on an empty stomach vs. with food; and the specific foods that you eat before/after taking omeprazole – could influence side effects.
  • Age: Clinical trial data indicate that some omeprazole side effects occur more frequently in pediatrics – than adults. For example, pediatrics using omeprazole are more likely to experience: adverse respiratory reactions, fever, and accidental injury – when compared with adults.  Additionally, it is thought that elderly patients may be at increased risk of certain side effects due to age-related decline in organ function.
  • Body size: It is reasonable to hypothesize that a person’s body size and/or composition could influence the likelihood of experiencing various side effects while using omeprazole. For example, someone with a large body size might need a larger dose of omeprazole to treat his/her symptoms – compared to someone with a smaller body size.  In any regard, the larger the dose of omeprazole that’s ingested relative to body size – the more likely side effects might occur.
  • Format: There are several different formats of omeprazole on the market including: oral pills, oral suspensions, and intravenous injections. In the United States, oral formats are the only option – whereas in other countries, intravenous injections may be an option (in addition to both oral formats).  While side effects don’t differ significantly among omeprazole formats, the intravenous format is generally associated with increased risk of “injection site reactions” as a side effect.  Furthermore, some individuals may report a greater number of side effects and/or different side effects with a specific omeprazole format (compared to another).
  • Genetics: Gene expression of the omeprazole user could influence how quickly omeprazole is metabolized, the potency of its effect, as well as the severities of its side effects. Pharmacokinetic studies indicate that omeprazole undergoes metabolism chiefly via CYP450 enzymes such as: CYP2C19 and CYP3A4, and to a lesser extent, CYP2D6.  Persons classified as CYP2C19 poor metabolizers (as a result of gene expression) may experience a greater number of severe side effects from omeprazole – compared to CYP2C19 rapid metabolizers.  (Source: https://www.ncbi.nlm.nih.gov/books/NBK100895/)
  • Lifestyle: The lifestyle of an omeprazole user could increase or decrease risk of medication-related side effects. If you do things like: exercise regularly; consume nutritious foods (with vitamins and minerals); eat a sensible quantity of calories; and manage your stress – these habits may offset or reduce the side effects that you experience while using omeprazole.  However, if you: overeat; never exercise; fail to manage stress; and avoid nutritious foods – you may be at increased risk of omeprazole side effects.
  • Medical status: Any medical conditions you have could impact the specific side effects that you experience while taking omeprazole – as well as the severities of those side effects. For example, someone with a history of tension-type headaches might be at increased risk of experiencing headaches as a side effect – compared to a person with zero history of headaches.  If you don’t have any medical condition (other than the condition for which you’re taking omeprazole), you may be at lower risk of certain side effects and reactions – than persons with preexisting conditions.

Strategies for reducing Omeprazole side effects

Included below are some strategies that might prove useful for reducing the prevalence and/or severities of side effects that are caused by omeprazole.  It is important to realize that the effectiveness of these strategies is not guaranteed – some users may find them helpful, whereas others may derive zero benefit.  Before utilizing any of the strategies outlined below, consult a medical doctor to ensure that they are safe and potentially effective.

  1. Omeprazole dose adjustment: If you’re struggling with omeprazole side effects, you may want to ask your doctor about a dosage adjustment. It is known that high doses of omeprazole can decrease stomach acid more than lower doses, but high doses are also more likely to cause side effects.  Your goal should be to find the “minimal effective dose” – or lowest quantity of omeprazole needed to manage your medical symptoms.  By administering the lowest effective dose, side effects will be less likely to occur.
  2. Treat side effects (with other agents): Side effects of omeprazole can sometimes be treated or managed with other substances. For example, if you’re experiencing headaches while taking omeprazole, you might benefit from “as-needed” use of an over-the-counter headache relief medication.  Using substances that counteract omeprazole’s side effects (without causing an interaction) is something to consider trying.
  3. Eliminate unnecessary substances: If you’re experiencing side effects while taking omeprazole, and you’ve been using other substances (supplements, medications, drugs, etc.) along with it, you may want to stop taking medically-unnecessary agents. Many substances interact with omeprazole (and vice-versa) and/or synergistically exacerbate its side effects.  By discontinuing all medically-unnecessary substances while taking omeprazole, you may notice that the medication becomes easier to tolerate.
  4. Review administration instructions: The way in which you administer omeprazole could explain why you’re experiencing unwanted side effects. Medical documentation suggests that it’s best to administer omeprazole delayed-release capsules and oral suspension formats at least 1 hour before a meal, first thing in the morning.  If you haven’t been administering omeprazole in accordance with medical instruction – reviewing and following administration instructions might help reduce side effects.
  5. Use for a longer time: If you’re a new omeprazole user, there’s a chance that some of the side effects you’re experiencing might be related to lack of physiologic adaptation to the medication. As your physiology becomes better-adapted to omeprazole (with longer-term use), side effects may abate or decrease in severity.  For this reason, if you’re in the early stages of treatment, you may need to use the medication for a longer duration for certain side effects to diminish.

Note: If you experience debilitating side effects from omeprazole, share them with a medical doctor as soon as possible.  In the event that side effect reduction strategies are unable to minimize your treatment-related side effects, you might need to consider omeprazole discontinuation and/or switch to a different medication. (Read more: “Omeprazole withdrawal symptoms“).

Have you experienced Omeprazole side effects?

If you’re currently taking omeprazole – or are a former omeprazole user, report the side effects that you experienced [from the medication] – in the comments section.  In your comment, mention the side effects that were harshest or most noticeable, and assign a numeric rating to each of those side effects (on a scale from 1 to 10, with “1” being minimal severity and “10” maximal severity).

To ensure that people reading this article are able to understand your situation, consider providing extra details such as: your omeprazole dose (e.g. 20 mg per day); the format you use (e.g. oral pills); the total duration of your treatment (e.g. 1 month); and concurrently-administered medications.

If you use other substances with omeprazole, have you investigated whether the side effects you’re experiencing might be due to an interaction effect and/or solely caused by the other substance(s)?  In your experience, do the therapeutic effects of omeprazole outweigh the side effects?  If you endured unwanted side effects during treatment, were there any strategies that you found helpful for reducing them?

In summary, while omeprazole is considered a safe and effective proton-pump inhibitor (PPI), not everyone tolerates it perfectly.  If you find yourself unable to tolerate omeprazole, inform your doctor as soon as possible and consider alternative treatment options.

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