Pristiq (Desvenlafaxine) is a drug that was approved for the treatment of major depression in 2007. It functions as an SNRI (serotonin-norepinephrine reuptake inhibitor) and increases extracellular levels of two neurotransmitters. In addition to treating depression, it is also being investigated as a non-hormonal approach to treating menopause.

This drug is considered very similar to the drug Effexor (Venlafaxine) – most consider it as being an “updated version.” Pristiq contains the active metabolite of Effexor and thus is relatively similar in its effects. The major difference between the two drugs is that Pristiq increases norepinephrine at nearly 3 times the amount of Effexor. While many find Pristiq effective as an antidepressant, it is capable of causing unwanted side effects, including weight changes.

Pristiq: Weight Gain or Loss?

Most people want to be reassured by their doctor that they will not gain weight when taking an antidepressant. Unfortunately it is impossible to make guarantees and predict which drug will cause you to gain weight and which will cause you to lose weight. In general, Pristiq is considered to be more weight neutral than the SSRIs – meaning that there’s less of a chance that you will gain weight.

Some individuals that take it will pack on the pounds, while others will end up losing weight. Others may end up staying at their normal baseline weight throughout treatment. It is believed that the norepinephrine reuptake inhibition helps offset the potential weight gain that would likely result from the serotonin reuptake inhibition.

How Pristiq Causes Weight Gain

There are several potential theories as to what may lead you to gain weight while taking Pristiq. If you’ve packed on some serious weight and you know it’s probably from the medication, below is a list of potential causes.

  • Appetite increase: Some people experience a noticeable appetite increase after they begin taking Pristiq. In other words, people feel hungry more frequently than they had prior to taking the drug. To cope with the hunger that they experience, they end up eating more. Others may gain some weight
  • Carb cravings: Any medication that affects the serotonin system has potential to create food cravings. Many people end up taking SSRIs and SNRIs and notice that they start to crave carbohydrates and other sugary foods. If you are craving pastas, pizzas, and candies, it may be a little more than a coincidence.
  • Drug interactions: It is important to keep in mind that Pristiq may not be the only culprit for your weight gain. If you are taking another medication, there’s always a possibility that Pristiq may be interacting with it to increase the amount of weight you gain. In some cases drugs work synergistically to slow the metabolism or make you pack on excess weight.
  • Fat storage: Most wouldn’t think that Pristiq would alter the way the body stores fat, but this is a theory to consider. If you were in good shape prior to taking Pristiq and you notice a build-up of fat in areas that were previously skinny, it’s likely a result of the medication. Some speculate that it may alter your body’s fat storage mechanisms over the long term.
  • Food taste: Certain people taking Pristiq end up experiencing an improvement in taste. This can lead to an increase in food consumption. If food didn’t taste very good when you were depressed and all-of-a-sudden it tastes amazing, you’re probably going to eat more.
  • Hormonal changes: It is possible that this drug alters hormone levels when taken over a long term. Some believe that changes in the levels of certain hormones may contribute to the amount of weight a person gains. For example, if a person’s level of cortisol increases throughout treatment, this could be a direct cause of gained weight.
  • Side effects: While Pristiq is considered an activating antidepressant, it doesn’t have this effect in every person. Some people may become groggy, tired, or fatigued while taking it. If you react to the drug by feeling sluggish or tired, you may be less likely to get proper physical activity or exercise, which could lead to weight gain.
  • Slow metabolism: Most people believe that Pristiq speeds up the metabolism, but not every person has this experience. If you believe that your metabolism slowed over the course of your treatment with Pristiq, you could be right.
  • Social eating: When people are depressed, they often isolate themselves from social events. When people feel happier, they are more likely to do things with friends and partake in social outings. Those that take Pristiq may start to feel happier and do things with friends, including social eating. Increasing the amount of times you go out to eat with friends is often a quick way to gain weight.

Note: In some cases weight gain is due to a combination of factors listed above. For others, there may be one primary factor that leads them to gain weight. Keep in mind that the way a person reacts to Pristiq is highly subject to individual variation.

How Pristiq Causes Weight Loss

Most people that lose weight while taking Pristiq do so within the first 6 months of treatment. It is common to experience weight changes during the first phase of treatment because the drug hasn’t had enough time to make long-term physiological alterations. Below is a list of reasons why people lose weight on Pristiq.

  • Appetite decrease: It is possible to take an antidepressant and experience a decrease in appetite. Those that aren’t as hungry as they were prior to taking the drug are more likely to eat less and end up losing some weight. While appetite decrease generally isn’t long lasting, it can cause some initial weight loss.
  • Diarrhea: A side effect of this drug is that of diarrhea. If you experience this side effect, it is likely a direct cause of weight loss. Anything that acts as a laxative is going to result in short-term weight loss. However, as your body stabilizes and adapts to the drug, you should gain the weight back that you lost via diarrhea.
  • Energy increase: Among some people, Pristiq tends to give them a significant increase in energy. If the person was depressed and sluggish prior to taking the drug, but now they are stimulated, they may be more likely to exercise and stay active. The increase in physical activity may lead to weight loss.
  • Metabolism increase: The fact that Pristiq increases extracellular norepinephrine results in stimulatory effects. The stimulation will speed up metabolism and could result in some degree of weight loss. In some individuals, the metabolic slowing from the serotonin increase is overridden by norepinephrine.
  • Nausea: A very common side effect associated with this medication is nausea. If you feel nauseous more than usual, you may be less likely to eat. Nobody wants to eat if they are feeling nauseous. Therefore this may be a direct cause of an appetite decrease and ultimately weight loss.
  • Vomiting: If you experience vomiting as a side effect of this drug, you are going to lose weight. Understand that this side effect generally subsides after a couple weeks and can be the cause of initial weight loss on this drug. Those that vomit over a longer span should seek immediate medical attention.

Why Pristiq is generally regarded as “weight neutral”

In clinical trials, Pristiq wasn’t found to produce any significant weight gain among those that took it. Therefore, the company that made the drug was able to promote it as a “weight neutral” antidepressant. This allows psychiatrists to tell patients that they won’t gain weight on this particular drug because it isn’t associated with any gain in weight. They can show the studies and results of them and suggest that if you gain weight on this drug, it’s your fault – not the drug.

Unfortunately this is a relatively skewed way of looking at things. In the clinical trials, some people likely gained weight, others likely lost a bit of weight, etc. Additionally clinical trials do not examine patients that have taken the drug for years – they simply analyze responses over a period of months. This may not fully reveal the potential to gain weight over a long-term treatment with Pristiq.

It’s important to keep in mind that anyone could still gain weight while taking this drug – especially over the long term. Everyone will have an individualized reaction and vary in the side effects that they experience. Although most evidence does suggest that the drug is weight neutral, it should be noted that some individuals will still likely gain weight from taking Pristiq.

Factors that influence weight changes on Pristiq

There are some other factors that you should keep in mind if you experience weight gain or loss while taking Pristiq. The factors that influence weight changes include: dosage of the drug, your lifestyle and habits, how long you’ve been taking the drug, and whether you are also taking other medications.

1. Dosage

At the moment, Pristiq is only recommended to be taken at the 50 mg dose. Those taking any dose higher than 50 mg are not getting any additional therapeutic benefit. Therefore, 50 mg is considered the minimal effective dose and only available dose of the drug. Despite the recommendation not to exceed 50 mg, some people still end up on higher doses.

The higher the dose, the greater potential a person has to gain weight from the drug. At higher doses, the drug is capable of making more changes to a person’s homeostatic physiology. The more control you give the drug over your functioning, the greater the likelihood that you’ll gain weight. Pristiq is offered at both 50 mg and 100 mg doses, but even 50 mg may feel too high for some individuals (especially those of smaller stature or size).  The greater the dose, the greater potential for weight fluctuation in response to the drug.

2. Individual factors

It is also important to consider individual factors that may be influencing weight changes. This includes things like your dietary intake, amount of exercise you get, your baseline bodyweight, sleep patterns, and stress levels. Your genetics also have significant influence over how you respond to the drug.

For this reason it is recommended to consider the “GeneSight” test that evaluates your genetics to predict how you will react to this drug. Always keep in mind that your lifestyle choices always have some potential influence over your weight, regardless of whether you are taking an antidepressant.

3. Time span

How long were you taking Pristiq? Those that take it over a shorter term are more likely to experience some sort of weight loss or remain weight neutral. It is believed that over the long term, weight gain is a more likely experience. This is because it often takes a long period of time (i.e. 6 to 12 months) for the drug to have made substantial changes to your physiological functioning and neurochemistry. The longer you’ve taken the drug, the more likely it is that you’re going to gain some weight (even if it’s a small amount).

4. Other medications/drugs

If you are taking any other medications (or drugs) in addition to Pristiq, it is important to consider that they also may be contributing to the amount of weight you gain. In some cases Pristiq can interact with other drugs and result in more weight gain than if you were only on a single medication.

Before you blame Pristiq for any weight gain, be sure to consider the fact that other drugs may also be contributing. Certain antidepressant augmentation strategies such as antipsychotics are very likely to cause weight gain. If you plan on discontinuing one medication to help minimize weight gain, be sure to talk to your doctor about it.

How much weight will you gain/lose from Pristiq?

There’s no research that documents the amount of weight gained or lost on Pristiq. Since a significant amount of weight wasn’t gained during clinical trials, researchers concluded that Pristiq is a “weight neutral” antidepressant and will not cause weight gain. The problem with this conclusion is that not everyone will find it to be weight neutral.

Some people will end up gaining a considerable amount of weight during the first 12 months (i.e. year) of treatment, while others may end up losing some weight. This demonstrates that Pristiq affects everyone differently. Certain people may lose 5 to 10 lbs. the first year of treatment, while others may gain 5 to 10 lbs. – there’s no telling how you’re going to react until you take it.

Pristiq: Cost-Benefit Analysis

If you are taking Pristiq, it is important to conduct a cost-benefit analysis of your experience. If the drug is working very well, a little bit of weight change may not be a big deal. For example, if you gain 5 to 10 lbs. your first year of treatment you may not care if your depression has markedly improved.

However, if you have packed on more than 10 lbs. (or lost a lot of weight), your depression hasn’t really improved, and you are experiencing other side effects, you may want to think about switching medications and/or Pristiq withdrawal. Always evaluate the benefits (improvements) resulting from your treatment and make sure they outweigh any costs (side effects).

Did you gain weight or lose weight on Pristiq?

If you have taken Pristiq, feel free to share any weight changes you experienced. If you gained weight while taking this drug, let us know how much weight you gained, whether you were taking the standard dosage, and how long you had been taking it. If you ended up losing a chunk of weight while on Pristiq, be sure to discuss how much you lost, and any factors that may have contributed to the weight loss. Others that have experienced no change in weight can also comment on their experience.

Feel free to mention any other factors that may have contributed to your weight gain and/or loss while on the drug. Did it boost your overall energy level? Did it make you feel more tired than usual or hungrier than normal? Although weight changes are common while taking the drug, most people eventually return to their baseline weight after they’ve discontinued Pristiq.