Remeron (Mirtazapine) is an atypical antidepressant that is technically classified as an “NaSSA” (noradrenergic and specific serotonergic) drug. It is considered a highly effective antidepressant, and some have posited that Remeron is superior in efficacy compared to other antidepressants. In a meta-analysis from 2009, it was found to be more effective than all SSRIs, SNRIs, and a couple other atypicals like Wellbutrin and Reboxetine.

Despite being considered the drug with the highest efficacy in that particular meta-analysis, most would agree that “the most effective antidepressant” is subject to significant variation based on the individual. Remeron is considered “fair” in terms of tolerability, with some patients having significantly less side effects than others. Unfortunately most people who take the drug notice that it significantly increases their appetite, which inevitably leads to weight gain.

Remeron and Weight Gain

Most professionals should be aware of the fact that people taking Remeron are likely to gain weight. Unlike most antidepressants in which short-term weight gain may not be as common, with Remeron it is likely that you’ll gain weight over the short and long term. Some argue that this is likely due to developing an increased appetite, but there are other theories.

How Remeron Causes Weight Gain (Theories)

Below is a list of theories and possible factors to consider that may contribute to weight gain while taking Remeron. Understand that although not everyone will gain weight from this medication, a significant number of people do. While it is known that a significant number of people gain weight as a result of appetite increase, there are other potential causal possibilities.

  • Fat mass increase: Some researchers believe that Remeron may cause weight gain by increasing fat stores throughout the body. If you notice that you’re developing fat in parts of the body that were previously thinner, it’s likely from the drug. It has been hypothesized that Remeron may be causing these fat storage changes by altering levels of leptin and TNF-alpha (tumor necrosis factor-alpha) cytokine system. In small-scale studies, it was found that plasma levels of TNF-alpha had markedly increased after a patients had taken Remeron for a month.
  • Food cravings (carbohydrates): Many people notice after they start taking Remeron, they develop food cravings. If there’s a particular food or type of food that you start to crave after you begin treatment with this antidepressant, it’s likely an effect of taking this drug. Most people notice that they crave unhealthy foods such as refined carbohydrates and sugars. It is believed that craving carbs can be influenced by altering levels of various neurotransmitters as well as glucose levels.
  • Hormone levels (Leptin): It is possible that Remeron may be altering levels of various hormones to produce weight changes. One that is clearly documented in research with this drug is the hormone “Leptin” which regulates fat storage.  The hormonal changes may become more significant over the course of a long-term, which may account for more substantial weight changes among long-term users.
  • Increased appetite: In some cases people are prescribed Remeron if they are underweight and/or under-eating. This drug is highly effective at increasing appetite to the point that people pack on a significant chunk of weight within the first month of treatment. It has been estimated that approximately 17% of those taking Remeron experience an increased appetite.
  • Metabolism decrease: It is fairly well-established that those taking antidepressants experience a decrease in metabolism. The decrease in metabolism means that even if you are eating the same number of calories that you were prior to taking the drug, you’re going to pack on weight while taking it. If the Remeron makes you fatigued or tired, this generally leads to less physical movement, which is also capable of slowing metabolism.
  • Interaction effects: Keep in mind that if you are taking any other medications, it may increase your propensity to gain weight as a result of interaction effects. Sometimes medications elicit synergistic “weight gaining” effects, leading to substantial weight gain in a short period of time. A common example would be prescribing Remeron with an atypical antipsychotic like Zyprexa. While it is unknown if there are synergistic effects of medications, some speculate that it is a possibility.
  • Social eating: Those who were seriously depressed or anxious prior to taking Remeron, but are now feeling happier (or less anxious) are more likely to hang out with friends and/or participate in social activities. If you notice that you start going out to eat with friends a lot after you began Remeron, keep in mind that this may be a direct reason as to why you are gaining weight. Eating out typically doesn’t (generally) provide the healthiest nor the most nutritious options and it increases the tendency that we will overeat.
  • Side effects: Another reason people likely gain weight on Remeron is that it can make certain individuals feel drowsy or fatigued. If you feel more fatigued than usual, you’re probably less likely to exercise and get adequate physical activity to keep your metabolism up. If your appetite increases and you feel fatigued, you are essentially going to eat more food and move around less; a common recipe for weight gain.
  • Taste improvement: In some cases, after a person starts taking Remeron, food tastes better. Some people who are depressed complain that food doesn’t taste good or tastes bland. If their depression is treated, they may experience an improvement in the way food tastes, which could lead them to eat more than they were in the past. The improvement in taste is believed to be caused by neurotransmitter alterations.

Note: For some people, there may be one specific factor that is leading them to gain weight. For others, it may be a combination of factor such as slowed metabolism, craving carbs, and an increased amount of social eating.

Factors that influence weight gain on Remeron

If you are gaining weight on Remeron, it is important to realize that a variety of other individualized factors should be considered. This includes things like: dosage you’re taking, your dietary intake, exercise habits, stress level, how long you’ve been on the drug, as well as whether you are taking other medications.

1. Dosage

Most people end up taking Remeron within the dose range of 15 mg to 45 mg on a daily basis. In general, the greater your dose in relation to your overall size and pre-treatment weight, the more likely it is that you’re going to gain weight. Those who are on substantially higher doses are considerably more likely to gain weight than individuals taking low doses.

Some have made the argument that low dosing with Remeron may be more likely to trigger weight gain due to more stimulation of the H1 (histamine) receptor.  They claim that the effects of H1 stimulation are counteracted by norepinephrine increases at higher levels.  Whether there is credibility to this theory remains to be true, but if you gain more weight at the low dose than the higher one, it may be somewhat valid.

It should still be assumed that at higher doses the drug will further alter your neurochemistry as well as physiological functions.  The greater the alterations as a result of the increased dose, the more likely it is that your homeostatic fat regulation, glucose levels, and leptin levels will be altered as a result of the drug.  This is why it is still recommended to take the minimal effective dose of most drugs, including Remeron.

2. Individual factors

It is also important to hold yourself accountable for any habits you’ve developed that may also be increasing your weight. While Remeron is very likely to cause weight, the foods that you choose to eat, how much sleep you get, your stress level, and amount of exercise you get can influence whether you gain weight. If you aren’t taking proper care of yourself and living a healthy lifestyle, you may gain weight as a result of the drug AND as the result of your unhealthy lifestyle.

Individual genetics may also influence whether you’re going to gain weight. If you are interested in determining how your genetics may be influencing your reaction to certain psychiatric medications, you may want to look into “GeneSight” testing. This test takes a sample of your genetic code and is able to determine whether you are likely to have a favorable reaction to a particular drug in terms of efficacy and side effects.

3. Time span

The length of time that you’ve been taking Remeron is another factor that may contribute to weight gain. The longer the duration over which you’ve been taking this drug, the more likely it is that you’ve built up some sort of tolerance. When people build up a tolerance, they typically increase the dosage (which we already know can lead to further weight gain).

Although in the case of Remeron people are likely to gain weight over the short term (i.e. 1 month), they may pack on even more pounds over the long-term. This is largely due to neurobiological changes as a result of long-term treatment. The drug will have altered your neurochemistry and disrupted homeostatic functioning to a significant extent which will cause you to gain even more weight.

4. Other medications

Do you currently take any other medications with Remeron? It is easy to blame Remeron for your weight gain, but do you know whether the other drugs your taking could also cause weight gain? Many people fail to investigate whether their other drugs may be an additional culprit for the amount of weight they’ve packed on while taking Remeron. In some cases, the other drugs that you’re taking may be causing more weight gain than your antidepressant.

In other cases the other drug(s) that you’re taking may be having a synergistic effect with Remeron to further enhance the amount of weight you gain. In other cases, the other drug(s) you’re taking may be the primary cause of your weight gain – especially if you are taking an antipsychotic.

How much weight will you gain from Remeron?

Since everyone responds to Remeron on an individual basis, there’s no telling specifically how much weight you’ll stand to gain. Most studies indicate that you will be likely to gain weight on both short-term and long-term treatment with Remeron. A number of factors mentioned above such as dosage and how long you’ve been taking the drug will influence the number of pounds you pack on.

In one small-scale 6-week study involving seven women, the average weight gain after 6 weeks was roughly 8 lbs; they also gained over half-a-pound of fat mass in this period. Some have gone as far as to speculate that lower doses have a higher affinity for the H1 histamine receptor which triggers an increase in appetite. At higher doses, norepinephrine levels tend to increase and counteract this effect – in some cases leading to no further weight gain.

Some people will end up gaining 10 lbs. others may gain up to 30 lbs. – responses tend to vary based on the individual. Just know that you’re probably going to gain anywhere from 5 to 10 lbs. throughout your treatment. For many people, their initial weight gain will hit a plateau and fortunately this weight is generally easily lost when the medication is discontinued.

  • Source: http://www.ncbi.nlm.nih.gov/pubmed/16649829

Will everyone gain weight while taking Remeron?

While not everyone may report weight gain on this medication, most people will gain some weight during treatment. Whether the amount of weight should be considered “significant” is up for individual interpretation. Formal studies have reported that nearly 30% of patients taking Remeron self-reported that they gained weight when on the drug for 10 months.

Over the course of a short-term (i.e. 12 weeks) approximately 20% of people report weight gain. Unless you are taking other medications to offset the weight gain, it is highly likely that you will gain weight on this medication. This antidepressant is extremely well known to cause an increase in weight. Fortunately, most people do not tend to gain additional weight after the first several months of treatment.

Remeron: Comparing Efficacy vs. Weight Gain

When taking any drug, it is important to conduct a cost-benefit analysis. This involves evaluating the severity of side effects (costs) and comparing them to the efficacy of the medication (benefits). If you have packed on a significant amount of weight to the point that the weight gain is making your depression worse, you may want to consider switching medications or talking to your psychiatrist about Remeron withdrawal.

In the event that the drug is working great, but you’ve gained some weight, it’s probably a good idea to continue treatment. It can be incredibly difficult to find a medication that effectively treats conditions like anxiety and depression. Finally, if the drug isn’t working well and you are experiencing an array of unwanted side effects, it’s probably a sign that you should pursue other options.

Did you gain weight while taking Remeron?

If you have experience taking Remeron or are currently taking it, feel free to share how much weight you gained. It would also be helpful to know the dosage you have been taking, as well as if you switched dosages (i.e. increased), how the dosage change affected your weight. Be sure to also discuss how long you’ve been on the medication, whether you’ve noticed any changes throughout the long-term and consider noting any other factors that you believe may have influenced your weight. Understand that sharing your experience may help someone else who has gone through (or is currently dealing with) something similar.