Mirtazapine Weight Gain: Why It Happens and What You Can Do

When you start taking mirtazapine, a tetracyclic antidepressant used to treat depression and anxiety. Also known as Remeron, it works by boosting serotonin and norepinephrine in the brain to lift mood. But for many people, one of the first things they notice isn’t improved sleep or reduced anxiety—it’s the scale going up. Mirtazapine weight gain isn’t rare. In fact, studies show nearly 2 in 5 users gain at least 7% of their body weight within the first few months. It’s not a flaw in your willpower. It’s biology.

This happens because mirtazapine strongly blocks histamine H1 receptors, which are tied to appetite control. That’s why people on it often report sudden cravings, especially for carbs and sweets. It’s not just hunger—it’s a physical urge. The drug also slows metabolism slightly and can make you feel more relaxed, leading to less movement. Unlike some antidepressants that suppress appetite, mirtazapine does the opposite. It’s designed to help people who’ve lost weight due to depression, but for others, that effect becomes too strong. If you’re already prone to weight changes, or if you’re on other meds that affect metabolism, the risk goes up.

Related to this are two other key players: appetite increase, a direct physiological response triggered by mirtazapine’s effect on brain chemicals, and psychiatric medications, a broad category that includes drugs known to cause metabolic side effects. Not all antidepressants do this—SSRIs like sertraline often cause weight loss early on—but mirtazapine stands out for its appetite-stimulating power. It’s also worth noting that weight gain isn’t always immediate. Some people don’t notice changes until after 3–6 months, which can catch them off guard.

Here’s the thing: stopping mirtazapine isn’t always the answer. If it’s helping your mood, you don’t want to trade depression for a lower number on the scale. But you don’t have to just accept it either. Small changes—like tracking food without strict dieting, adding short walks after meals, or swapping snacks for protein-rich options—can make a real difference. Talking to your doctor about adjusting the dose or timing (taking it at night might reduce daytime cravings) can also help. Some people switch to another antidepressant, but that’s not always safer or easier.

Below, you’ll find real-world insights from people who’ve lived with this side effect, plus comparisons with other meds, tips on managing cravings, and how to talk to your doctor without feeling judged. These aren’t generic advice posts—they’re grounded in actual experiences and clinical data. Whether you’re just starting mirtazapine or have been on it for months, you’ll find something useful here.