Mirtazapine Weight Gain Calculator
Estimate Your Weight Gain
When you start taking mirtazapine for depression, you’re not just treating your mood-you’re also changing how your body handles food, hunger, and energy. Many people are surprised when they notice the scale creeping up, sometimes quickly. It’s not just about eating more. The science behind why mirtazapine causes weight gain is complex, but understanding it helps you take control. This isn’t a myth or a rare side effect. It’s a well-documented, common outcome that affects about 1 in 4 people who take it.
Why Mirtazapine Makes You Gain Weight
Mirtazapine doesn’t just make you hungry. It rewires your body’s signals around food and energy use. At its core, this drug blocks histamine H1 receptors more strongly than any other commonly used antidepressant. That’s the key. Blocking H1 receptors increases appetite, especially for carbs and sweets. In one 2019 study, healthy men on mirtazapine for just seven days reported a sharp rise in cravings for sugary foods-even when their calorie intake was controlled. Their bodies started burning more carbs and storing more fat, regardless of how much they ate.
It’s not just hunger. Mirtazapine also lowers your resting energy expenditure. That means your body burns fewer calories at rest. One study found a 5-7% drop in energy use, which adds up over weeks and months. Combine that with increased insulin release and higher triglycerides, and you’ve got a perfect storm for fat storage. Even if you don’t gain much weight, your body composition can shift toward more fat and less muscle.
What’s surprising is that this isn’t just about dosage. People think lower doses are safer for weight gain, but the truth is more nuanced. Mirtazapine’s receptor binding doesn’t change much between 7.5 mg and 45 mg. Higher doses might feel less sedating because of increased norepinephrine activity, but the appetite and metabolic effects stay strong across the range.
How Much Weight Do People Actually Gain?
Numbers vary, and that’s important to know. Some sources say 25% of users gain 7% or more of their body weight-that’s about 11 pounds for someone who weighs 150. But real-world data tells a more layered story. The STAR*D trial showed an average gain of 3.5 kg (7.7 lbs) over 12 weeks. Other studies, like UPMC’s analysis of 12 trials, found only 3 lbs (1.36 kg) in the first 8-12 weeks. That’s not nothing, but it’s less than the scary stories online suggest.
And then there are outliers. On Reddit, someone wrote they gained 35 pounds in six months. On Facebook support groups, you’ll find stories of 50- or even 100-pound gains. But here’s the reality: a 2022 survey of over 1,800 mirtazapine users found only 12% gained more than 20 pounds. Most people gain between 5 and 15 pounds. The extremes get attention, but they’re not the norm.
Interestingly, some people use mirtazapine for weight gain. Cancer patients with cachexia, people recovering from eating disorders, or those with severe nausea often benefit from its appetite-stimulating effects. A 2024 JAMA Oncology trial showed patients on mirtazapine ate more protein and fat-without necessarily gaining weight. Their bodies used the extra calories to rebuild muscle and strength, not just store fat.
How Mirtazapine Compares to Other Antidepressants
If you’re worried about weight, not all antidepressants are equal. A 2020 analysis of 21 different drugs found mirtazapine ranked second for weight gain-right behind paroxetine. It causes significantly more weight gain than sertraline, escitalopram, or fluoxetine. Bupropion is the opposite: it often leads to weight loss. In fact, some doctors prescribe bupropion to patients who’ve gained weight on other antidepressants.
Here’s a quick comparison based on average weight change over 12 weeks:
| Medication | Average Weight Change | Rank for Weight Gain |
|---|---|---|
| Mirtazapine | +3.5 kg (7.7 lbs) | 2nd |
| Paroxetine | +3.7 kg (8.2 lbs) | 1st |
| Citalopram | +1.8 kg (4.0 lbs) | 5th |
| Sertraline | +1.2 kg (2.6 lbs) | 8th |
| Bupropion | -0.6 kg (−1.3 lbs) | 21st (weight loss) |
| Venlafaxine | +0.5 kg (1.1 lbs) | 19th |
If weight is a major concern, switching to bupropion or sertraline might be a better long-term choice. But if your depression is severe, insomnia is a problem, or you’ve lost too much weight, mirtazapine’s benefits might still outweigh the risks.
What You Can Do to Limit Weight Gain
It’s not inevitable. There are practical steps you can take that make a real difference.
- Start low. Begin with 7.5 mg instead of jumping to 15 or 30 mg. One study found 7.5 mg caused 42% less weight gain than 30 mg over 12 weeks.
- Dose at night. Taking it in the evening helps you sleep, but it also reduces daytime cravings. A 2019 study showed people who took mirtazapine at night had fewer carb cravings during the day than those who took it in the morning.
- Focus on protein. A small 2022 pilot study showed that eating 1.2-1.6 grams of protein per kilogram of body weight (for a 70 kg person, that’s 84-112 grams daily) cut weight gain by 63%. Protein keeps you full, stabilizes blood sugar, and helps preserve muscle.
- Monitor your numbers. Get your weight, waist size, and blood work done before starting. Check in monthly for the first three months. Your doctor should track triglycerides and HbA1c-mirtazapine can raise these even without major weight gain.
Some people try adding low-dose naltrexone (LDN), a drug that blocks the brain’s reward response to food. Early trials show it cuts mirtazapine-related weight gain by over half. While not yet standard, it’s being studied actively. If you’re concerned, ask your doctor about it.
When Mirtazapine Might Still Be the Best Choice
Just because it causes weight gain doesn’t mean you should avoid it. For some, it’s the only antidepressant that works. If you have severe insomnia, anxiety with appetite loss, or cancer-related weight loss, mirtazapine can be life-changing. It’s one of the few antidepressants that improves sleep, appetite, and mood all at once. In geriatric psychiatry, it’s used in over 20% of cases. In palliative care, it’s a go-to for boosting food intake.
The key is matching the drug to the person. If you’re underweight, struggling to eat, or have trouble sleeping, the weight gain might be a side effect you’re willing to accept. If you’re already overweight or have prediabetes, you need to plan ahead. Talk to your doctor about alternatives-but don’t stop mirtazapine abruptly. Depression can come back harder than before.
What the Future Holds
Pharmaceutical companies know this is a problem. Merck has filed a patent for a new version of mirtazapine with 87% less H1 receptor activity-meaning it might keep the mood benefits without the hunger. Clinical trials are underway. Meanwhile, researchers are testing combinations like mirtazapine plus naltrexone, which looks promising in early results.
But for now, the drug remains widely used. In 2022, over 6 million prescriptions were filled in the U.S. alone. It’s not going away. What’s changing is how we use it. Doctors are more aware now. They’re starting lower, monitoring closer, and pairing it with nutrition advice instead of just saying, “It’s a side effect.”
If you’re on mirtazapine and worried about weight, you’re not alone. And you’re not powerless. Small changes in timing, diet, and dose can make a big difference. The goal isn’t to avoid the drug-it’s to use it wisely.
Does mirtazapine always cause weight gain?
No. About 25% of users gain 7% or more of their body weight, but many others gain little to none. Some even lose weight, especially if they were underweight before starting. Genetics, baseline weight, diet, activity level, and dose all play a role. It’s not guaranteed, but it’s common enough to plan for.
Can I prevent weight gain by taking a lower dose?
Starting at 7.5 mg instead of 30 mg can reduce weight gain by over 40%. Lower doses still help with sleep and mood, and the appetite-stimulating effects are less intense. But don’t stop increasing the dose if your depression isn’t improving-talk to your doctor. There’s a balance between effectiveness and side effects.
Is the weight gain mostly fat or muscle?
Mostly fat. Mirtazapine increases insulin and shifts metabolism toward storing carbohydrates as fat. Muscle mass doesn’t increase unless you’re actively strength training and eating enough protein. Without those interventions, the weight you gain is primarily adipose tissue.
Will I lose the weight if I stop taking mirtazapine?
Not necessarily. Once fat is stored, your body holds onto it unless you create a calorie deficit. Stopping the drug may stop further gain, but it won’t reverse what’s already there. Combining medication changes with diet and exercise gives you the best shot at losing the extra weight.
Are there any antidepressants that help with weight loss?
Yes. Bupropion (Wellbutrin) is the most consistent for weight loss, with studies showing an average loss of 0.6 kg over 12 weeks. Topiramate (off-label) and liraglutide (for depression with obesity) are also being studied. But these aren’t replacements for everyone-mirtazapine’s sleep and appetite benefits are unique.
