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Krill Oil Side Effects & Adverse Reactions

Krill oil is a supplement that can be taken to increase levels of omega-3 fatty acids. It has quickly gained popularity in part due to savvy marketing, but also as a result of the belief that the omega-3s contained in krill are more efficiently absorbed by humans because our cell walls consist of phospholipids; therefore the body doesn’t need to do any major conversion to attain the omega-3s.  Krill oil also contains an antioxidant known as “astaxanthin” which is believed to help slow aging, protect the skin, and improve brain function.

The other primary argument in favor of krill oil vs. fish oil is that krill is considered the world’s largest biomass. Meaning there are so many krill, that significant harvesting of them can be conducted without coming close to endangering the species. While many of the krill oil benefits aren’t adequately supported by science, this hasn’t stopped the masses from hopping on the latest trend of krill oil supplementation.

As more people have started using krill oil, there have been an increase in the number of reported side effects. Although most people don’t notice any detrimental side effects from taking krill oil, it is important to realize that any supplement can cause side effects.

Factors that influence krill oil side effects

There are several factors that influence the side effects a person experiences from taking krill oil. These factors include things like: quality of the krill oil, ingredient composition (per serving), the dosage a person takes, whether they’re taking other drugs (leading to interactions), as well as individual factors (e.g. genetics).

1. Quality

If there are concerns over the quality of the krill oil that you’re taking, it could be that the poor quality is directly causing your side effects. Before assuming that the krill oil itself is the cause, consider the fact that many krill oil supplements have been subject to oxidation, expiration, or are of poor quality. If you’re taking a low quality krill that hasn’t been tested by the IKOS, there’s a greater likelihood of adverse effects.

I’ve written a comprehensive analysis of the best krill oil supplements – check it out if you want to find the highest quality brands. Highest quality means that the krill oil will be free of heavy metal toxicity, PCBs, dioxins, and will be fresh. Just think of all the adverse effects that could result if you don’t do your research and unknowingly swallow a krill oil supplement that is rancid or laced with contaminants.

2. Ingredient composition

The varying ingredient composition within krill oil supplements may influence whether you experience side effects. Certain krill oils contain more omega-3 fatty acids (DHA and EPA) than others. For some individuals, the DHA may be more problematic than the EPA (and vice versa).

The amounts of omega-3 fatty acids, astaxanthin, and phospholipids can all influence whether you experience side effects. It is also important to keep in mind the ingredients that were used to create the “soft gel” or capsule that contains the krill oil. If you have an allergy to any of the ingredients contained within the capsule, these may provoke side effects.

3. Dosage

How much krill oil are you taking on a daily basis? Those that take higher doses may find that it helps reduce triglycerides, but higher doses tend to result in more side effects. For this reason, you should attempt to find the “minimal effective dose” even with a supplement like krill oil. By taking the minimal effective amount, you may be able to avoid the unwanted effects (e.g. blood thinning) that are often a byproduct of high dosing.

If you think that you may be taking too high of a dosage, be sure to talk to a medical professional for advice. Even moderate doses can be problematic and lead to unwanted side effects for certain people. Taking a low dose will help minimize any adverse reactions and/or potential dangers of krill oil consumption.

4. Interactions

Any anticoagulant and antiplatelet drugs are known to interact with krill oil supplements. Therefore if you are taking these drugs, know that krill oil may amplify their effects, resulting in increased bruising, bleeding, and/ slowed blood clotting. Krill oil interacts with a variety of medications including: Aspirin, ibuprofen, naproxen, warfarin, and several others. Talk to your doctor if you are on any medication and plan on supplementing krill oil.

Other medications may alter the absorption of krill oil, resulting in unwanted effects. Ideally, you’ll want all other medications fully out of your system before you start taking krill. If you take krill and another drug or supplement, always verify the safety to avoid contraindications.

5. Individual Physiology

It is also important to consider individual physiology and genetics when discussing side effects of krill oil. Why can two people take the same brand and dosage of krill oil, yet one person experiences no side effects, and the other gets a headache? It’s likely due to individual physiology and genetic responses.

Some people are more sensitive to supplementation, particularly of a small coldwater oceanic creature that may have never been in their diet. While krill oil is generally safe for most people, if you experience side effects, it may be a warning sign from your body that krill oil isn’t compatible with your physiological profile. If you have a sensitivity to omega-3 fatty acids, astaxanthin, or seafood – this could explain your side effects.

Krill Oil Side Effects: List of Possibilities

Below is a list of commonly reported side effects from people that have taken krill oil. Keep in mind that a majority of people taking krill oil don’t report any significant effects throughout their supplementation. Realize that the severity and number of side effects that you experience is subject to individual variation.

  • Agitation: In some cases, the krill oil supplementation may elevate levels of omega-3 fatty acids in the brain. This enhances neurotransmission and can result in increased energy levels. While the increased energy may seem beneficial, it can sometimes manifest as agitation, making it difficult to function.
  • Anxiety: While some purport that one of krill oil’s benefits is its ability to reduce anxiety, others end up experiencing increased anxiety from supplementation. If you experience an increase in anxiety, it’s likely a result of the omega-3s within the oil that over-activate brain activity and certain neural pathways.
  • Bloating: Many people notice that after they take their daily supply of krill oil, they begin to feel bloated. Bloating is a common side effect of krill oil supplementation and one that most people are willing to put up with. If the bloating is severe, it’s probably a good idea to stop taking the krill. For most people, the bloating occurs on a random basis and is pretty easy to tolerate.
  • Blood thinning: A common side effect associated with krill oil is its blood thinning effect. When taken at high dosages, krill oil is a very potent anticoagulant (blood thinner). Too much of a blood thinner can result in excessive bleeding and other unwanted effects. To avoid this effect, keep tabs on your dosing and don’t take too much.
  • Burping: Another extremely common side effect associated with krill oil is that of “burps.” We’ve all had cases of burping after swallowing any type of oil, and it can be unpleasant. You may notice the resurfacing of a krill taste in your mouth with each consecutive burp. Most people aren’t too bothered by this, but if it’s a problem, you could switch to a different krill supplier with an alternative encapsulation modality; this may reduce the burping.
  • Constipation: If you’ve noticed an increase in constipation after taking krill oil, it could be affecting your digestion. It has been reported that krill oil can make some people feel more constipated than usual. Should this become a problem, it’s probably a good idea to stop taking it.
  • Depression: Despite the fact that many people claim krill oil helps improve their mood, others have found that krill oil actually amplifies their depression. This may be a result of increasing brain activity in certain areas and/or the omega-3 fatty acid contents altering neurotransmitter levels and efficiency. If you notice yourself becoming increasingly depressed after supplementation, it’s probably a good idea to discontinue.
  • Diarrhea: Krill oil can affect the digestive system different depending on the person. In one person it may cause constipation, while for someone else it may cause diarrhea. This effect is most likely to stem from an allergic reaction, contaminated product, or expired batch of krill oil. Obviously if you experience loose or runny stools, it’s probably smart to discontinue.
  • Gas: Have you noticed an increase in flatulence after you started taking krill oil? Many people notice that it disrupts their digestion and can result in constipation, indigestion, and ultimately the passing of gas. This isn’t the worst side effect, but may feel uncomfortable if it persists.
  • Heartburn: Some people have complained about heartburn associated with krill oil supplementation. One suggested solution to avoid the side effect of heartburn is to take krill oil with a full meal. If the heartburn becomes difficult to deal with, try reducing your dose or discontinuing for awhile.
  • Hyperactivity: Certain individuals may notice a significant increase in both physical and mental energy with krill supplementation. It is believed that the omega-3 fatty acids may provoke a stimulatory response in sensitive people, leading to varying degrees of hyperactivity, with a difficulty remaining calm.
  • Insomnia: The omega-3 fatty acids (DHA and EPA) within krill oil can significantly bolster energy levels and brain activity. Dopamine levels may increase and brain activity may become quicker – both of which may contribute to insomnia. If you’ve found it difficult to sleep at night due to racing thoughts before bed, it may be worth stopping the krill oil.
  • Nausea: Feeling nauseous as a result of krill oil supplementation is a sign that you may have taken a rancid batch, an allergic reaction, or that you’re unable to tolerate it. Nausea is generally a warning sign that a foreign substance is incompatible with your physiological homeostasis.
  • Sleep disturbances: Some people notice a stimulating effect from supplementation of krill oil. This is likely a result of the omega-3 content, but the phospholipids and astaxanthin may also contribute to enhancing this effect. The increase in neurotransmitters and efficiency of neurotransmission can result in sleep difficulties such as insomnia, which stem from anxiety.
  • Tiredness: It’s relatively uncommon to feel increasingly tired from the krill oil. Tiredness may initially occur when a person first starts supplementing the krill, but should not be excessive. Certain individuals who are hyperactive can sometimes notice their energy level drop temporarily as they become calmer. This should not be mistaken for excessive fatigue which may signify an allergic reaction.
  • Upset stomach: If you notice an upset stomach on a consistent basis after taking krill oil, you may want to consider reducing the amount you’re taking. Various krill oil users have reported discomfort and even pain when taken at high doses. This could be a sign that the particular batch of krill you purchased wasn’t pure.

Krill Oil Adverse Reactions

Any adverse reactions to krill oil supplementation typically stem from an allergic reaction and/or medication interaction. That said, taking krill oil that is past the expiration date or from an unreliable source may also contribute to adverse effects. It is important to ensure the quality, purity, and freshness of your krill oil before consumption to avoid any potential adverse reactions.

  • Abdominal cramps: Some people may notice the minor side effect of bloating or gas, but when abdominal cramps ensue, it may be a sign of a more serious problem such as an allergy to the product. While these are generally uncommon, it is important to understand that they could be caused from the krill oil.
  • Appetite loss: If you notice that your appetite has significantly dropped, it could be chalked up to the krill supplementation. While this is a very uncommon reaction, it may be a result of a dopaminergic sensitivity stemming from increased concentrations of omega-3 fatty acids. The appetite drop may be a result of krill oil’s effect on digestion and/or causing nausea.
  • Bloody nose: Have you noticed that your nose started bleeding randomly after taking krill oil? Although this is a rare, adverse reaction, it does occur in some individuals. If you stop taking the supplement and the frequent bloody noses subside, it’s clear that the krill was the cause.
  • Blood pressure: You may notice a drop in your blood pressure when supplementing krill oil. The only problem is that at high dosages and/or when utilized in combination with beta blockers, blood pressure may drop to abnormally low levels. If you suspect that your blood pressure has been affected, seek immediate medical attention. Low blood pressure could lead to fainting and/or unconsciousness.
  • Breathing difficulties: If you notice a tightness in your chest and or are starting to have problems with breathing, it could be a sign that you’re allergic to krill oil. Any breathing difficulties should be discussed with a doctor as soon as they are noticed.
  • Dizziness: If you become dizzy or experience vertigo from krill oil, it could be a bad batch, or it could be that you just don’t tolerate it. This is another sign of an allergic reaction, but could also stem from the influx of omega-3 fatty acids. As the brain adapts to the increase in omega-3s, neurotransmission or neural pathways may become altered; making you dizzy.
  • Excessive blood thinning: Perhaps the most notable concern and most common is that of excess blood thinning. While a little blood thinning can be beneficial under medical supervision, too much can lead to slowed clotting and excessive bleeding with scrapes and cuts. This can end up being dangerous and should be avoided.
  • Irregular heartbeat: Have you noticed changes in your heartbeat after taking krill oil for awhile? While the supplement is thought to help improve cardiovascular health, not everyone experiences this benefit. Some people have weird reactions that cause their heart rate to drastically increase or become irregular.
  • Itching: If your skin starts to itch, it could be a sign that you’re having an allergic reaction. To mitigate the itching, you may want to stop taking the krill oil for awhile and determine whether it goes away. If the itching subsides in conjunction with discontinuation, it’s a sign that krill probably isn’t for you.
  • Skin rash: If you notice that your skin breaks out in hives, you probably are allergic to something within the supplement. This is an adverse reaction, but can affect those who have a seafood allergy. Discontinuation will generally allow the rash to clear up, but check with your doctor to be on the safe side as you may need to detox.
  • Stomach acid: Individuals who have stomach acid build-up prior to taking krill oil may find that supplementation makes it worse. If you feel as if the acid in your gut is mounting with each consecutive krill oil capsule you pop, it may not be a good fit for you.
  • Sweating: While relatively uncommon, some people notice an increase in perspiration after they start taking krill oil. If you begin to sweat excessively and can pinpoint this reaction to the krill oil, it’s likely an obvious warning from your body that you aren’t able to tolerate it.
  • Swelling: An obvious sign of an allergic reaction to krill oil is swelling throughout various parts of the body. If your lips, face, and/or other areas of your body become puffy, it could be a result of the supplement. Should you experience swelling, the supplementation should be discontinued.
  • Weakness: If you notice that your muscles or body begins to feel weak, you may be victim of an allergic reaction. Anything that is making you feel weaker doesn’t make logical sense to continue.
  • Taste changes: Some people complain about a bad or unwanted taste stuck in their mouth after they’ve been taking krill oil for a prolonged period. This is extremely uncommon but something to consider if you notice that food starts to taste worse than it did prior to supplementation.
  • Vomiting: Some people start feeling sick when they take krill oil. Krill isn’t considered a dietary staple and humans did not evolve to eat krill. Vomiting could be a sign of an allergic reaction or a signal that krill oil is not right for your particular body.

Note: If you experience any of the following adverse effects, it’s imperative to seek the help of a medical professional and discontinue your krill oil.

Krill Oil: Weighing the Benefits vs. Side Effects

Obviously if you are allergic to seafood, you should avoid taking krill oil supplements as an allergy will provoke numerous (potentially dangerous) side effects. If the side effects are odd such as itchy skin, puffy lips, or hives – you’ve probably got some sort of allergy. Preliminary research indicates that krill oil supplements are unlikely to cause unwanted side effects nor adverse reactions.

However, keep in mind that everyone is different. Just because most people don’t experience any side effects doesn’t mean that you are the exact same. Also be sure to consider the quality of the krill oil that you’re consuming before automatically assuming that you won’t tolerate all forms of krill oil. Purchasing from an untrustworthy company, storing krill oil improperly, taking too high of a dose, or using other drugs (or supplements) simultaneously – is a recipe for a greater number of side effects.

Chances are if you’re getting any benefit from krill oil supplementation, you’ll want to continue using it. However, if you aren’t really getting any noticeable benefit after consistent supplementation for a protracted period of time, you may want to forgo the krill oil and take a look at other options. Also keep in mind that if you do experience side effects, be sure to seek out an opinion from a medical professional.

It is important to listen to your body and trust your own experience when taking krill oil. Although you may experience benefit from krill oil, it isn’t a utopian supplement for everyone, and could theoretically exacerbate unwanted symptoms of certain conditions like anxiety. To determine how you are affected by krill oil, evaluate your physical and/or mental performance every few weeks to gauge changes.

If you’ve taken krill oil and noticed any side effects, feel free to share your experience in the comments section below. Discuss the severity of the side effects, how you know they’re from the krill oil, the dosage you had been taking, etc. By providing as many details as possible, it will help others better understand your situation.

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{ 25 comments… add one }
  • Kristin August 14, 2018, 6:22 pm

    I have been on krill oil 500mg per day for about a month. I have noticed a change in my mood and energy. I have felt down. Also have experienced sleep issues at least two times per week – not able to sleep at all. My doctor wanted me to try to help lower triglycerides. I think I should stop.

  • Oscar May 5, 2018, 7:39 pm

    I have been taking a large dose of krill and found I had to avoid taking it too close to bedtime, since it was causing insomnia. Flatulence and diarrhea are constant problems with it as well.

    The worst side effect came when I woke up one morning with my arms twitching, and later that day, in the hospital, I had a severe, myoclonic seizure.

    None of the doctors could tell what had caused it, since they found no nerve damage on a standard neurological exam and CT-scan. I could not type and had difficulties with motor control for two or three days afterwards.

    I did more research on krill later and found reports of it causing seizures! My wife took it for a while and found it was causing her to become agitated and angry all the time. On the plus side, it helps my thought processes, makes me more creative and alert, and gives me more energy.

    I have decided to compromise and take a much lower dose of krill, but the flatulence and diarrhea persist.

  • Stu April 14, 2018, 10:15 am

    Started having dizzy spells and joint pain was not going away. Now back on the cod liver oil. Back to normal.

  • Michele March 29, 2018, 7:32 am

    Took one gel cap of krill and never again. OMG, the side effects are terrible. This stuff should not be sold. I drank so much water to flush this horrible stuff out of my body. Terrible, terrible, terrible stuff. Beware, do not take this stuff.

  • Heidi January 18, 2018, 10:29 pm

    I took and completed 2 full bottles last year. 3 Subconjunctival Hematomas in 4 months later, it was the Megared Krill Oil. It acts like a blood thinner and I ran to the Eye Dr., and she didn’t know! Stopped taking it. Just Cod Liver oil 2 caps daily a) for depression b) for immune system c) for breast health d) for asthma. No more Oil of the Krill!!!

  • Dianne January 11, 2018, 4:24 am

    Started taking krill oil supp. Today woke up with lower stomach cramping later became very dizzy very faint vomiting and diarrhea. Went to ER. I really thought I was going to die. So I pretty sure it was the krill. Anyone this happened to? I am still very scared.

  • Sandye Garcia December 17, 2017, 6:08 pm

    After three days of 350 mg. krill oil I awoke at 6:00 am needing to poop and vomit. Felt like I was dying. Finally threw up. Slept half the next day. 3 days sick to my stomach, headache and tons of gas and no appetite. I cringe when I even think about krill oil. Bad stuff!

  • Linda March 2, 2017, 4:46 pm

    I started taking Viva Naturals Krill for joints. Developed nosebleeds after 2 weeks. It’s been 6 days and I am still having nosebleeds. Hoping it will soon be out of my system. Anyone know how long it stays in the system?

  • Liz` February 3, 2017, 4:57 pm

    I’m an avid runner who developed pain in a hip. PT/Chiro only managed to move the pain to other joints, so a friend recommended Mega Red Krill Oil. After a week or two, my hip felt great but I also was experiencing near-crippling depression. I stopped the Mega Red, and after a few days things started looking up.

    Hip started hurting again, took the Mega Red hoping it was just a coincidence. Nope, right as the hip got better, driving my car off a cliff started sounding better and better, too. Now, over year later, my hip is killing me, so once again I turned to krill – still hoping for coincidence.

    But here I am, with a bloody fist from punching the roof of my car, tears streaming down my cheeks because the roads are icy and a woman cut me off in traffic, and thinking how glorious it would be to drive off into the wilderness and never be heard from again. I’m pretty sure it’s not a coincidence.

    • Heidi April 18, 2018, 10:27 pm

      Please stop taking that! Check out Market America’s OPC for your hip. I have MDD, so I have been where you are. Do not end it all, life will get better. Cod Liver Oil is my mainstay for depression and a low dosage of meds.

  • K January 7, 2017, 4:00 pm

    I’ve been taking krill oil for about 2 weeks and I’ve had horrible insomnia, stomach cramping, nausea, and diarrhea.

  • Carolyn November 13, 2016, 12:27 pm

    I took krill oil 2000mg with dinner today. About an hour or so later felt sick. Have severe diarrhea. Omg not taking any more. First time I took it.

  • Jacob November 9, 2016, 5:58 am

    I seem to be having a unique allergic reaction. Burning in the head, lack of energy, smarting eyes and in areas of nerve damage where I have no feeling sudden pings of icy pain. (300 mg krill oil).

  • Wade September 7, 2016, 4:07 pm

    Never take this stuff! I thought I was dying.

  • Irma. L. Hausdorff May 26, 2016, 3:40 am

    I took a krill pill and had severe itching similar to what I get when exposed to cats. It was unbearable.

    • Heidi April 18, 2018, 10:29 pm

      I can’t believe I took krill oil and had the eye bleeds, also I have an EpiPen for shellfish!!! Everyone be careful and listen to your body!!!

  • Doris April 23, 2016, 6:49 pm

    I took 6 gel caps of UltraKrill and my nose started to bleed. My gums were bleeding to the point my periodontist couldn’t believe the damage that it had done. My face became swollen and stiff. I had 2 skin abscesses on my back. I felt a tightness in my chest. Food doesn’t taste the same and this is still 2 months after I stopped taking the krill. Wish I never took it!

  • Iris black April 4, 2016, 9:47 pm

    I took two krill oil capsules for about 6 days and felt ok but went to bed on the seventh night woke up with unbearable stomach cramps and diarrhea then started passing quite a lot of blood ended up being hospitalized for 3 days. Tomorrow I am going to have a CT colonography done to see what’s going on in my bowel.

    I didn’t realize I should not have been taking the Krill oil as I was also taking aspirin which also thins the blood also. Never had any trouble until I started to take the krill. It may not have been krill oil that done damage but I wish I had never taken it in the first place. Be warned people.

  • Simone March 26, 2016, 3:10 pm

    Last night I took one Finest Nutrition Krill Oil 300mg soft gel. This morning from my right elbow down is swollen pretty bad all the way to my finger tips. Not going to take another one. Returning today.

  • eileen haydon January 22, 2016, 7:41 am

    I started taking wild krill 333mg. Had terrible constipation/BLOATING. Never in my life have I experienced this. In terrible pain now for 2 days. Have only been taking 2 a day with meals since last Saturday, that’s it. I realize what’s causing it… took 2 today – that’s it, no more.

  • IQBAL October 28, 2015, 6:30 am

    I have been taking Krill oil for the last around one year now. I have observed a positive significant improvement in my Cholestrol, Triglycerides, HDL and particularly LDL. But I have experienced severe bloating, Constipation, upset stomach and even loss of appetite. It has increased so much that I have stopped taking Krill oil. I was taking 1000mg one tab daily or 500 mg 2 tabs daily. Any guidance?

  • Cathy October 13, 2015, 11:41 pm

    I had to take several naps during the day when I started taking 500mg of krill oil softgels. I just could not stay awake for the 2 weeks I took them. I stopped 2 days ago and am back to normal.

  • bennie August 1, 2015, 4:56 pm

    I used krill oil for almost a year, skin broke out in bumps. Had diarrhea I didn’t want to believe it was the krill oil. After going off the krill oil twice symptoms went away. I was using Mega Red by Schiff then I tried viva labs krill the symptoms returned!

    • James Lim December 2, 2015, 3:51 pm

      You had diarrhea for the whole year?

  • Bridgette May 20, 2015, 11:04 am

    I noticed that after taking Krill for about 3 weeks I started having severe itching and ant bites type rash that was very painful that also affected my muscles in that area mostly my legs and groin area. Also had constipation as well. Finally researched the side effects and stopped taking to see if all those side effects would stop. Will try and post after a week or two.

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