Antidepressants and Weight Gain
Antidepressant medicines differ widely in their effect on weight, with some adding several kilograms over months while others are weight-neutral or cause early weight loss.
Plain English
Patient-Friendly Explanation
Depression itself changes appetite and weight, sometimes upwards and sometimes downwards, and the medicine prescribed adds its own effect on top. Among the commonly used antidepressants, mirtazapine is the one most likely to cause noticeable weight gain, and older tricyclic drugs such as amitriptyline also tend to increase weight. Within the selective serotonin reuptake inhibitor group, paroxetine carries the highest risk of weight gain, while sertraline and fluoxetine are closer to neutral, and fluoxetine can cause weight loss at the start. Bupropion is usually weight-neutral and may reduce weight a little. Venlafaxine and duloxetine are generally weight-neutral. Weight gain usually develops over weeks to months and is often several kilograms, and it is not simply a matter of discipline. If weight is becoming a problem, the answer is to discuss a possible change or dose adjustment with the prescriber rather than to stop the medicine suddenly, which can cause withdrawal symptoms and relapse.
Medical
Clinical Definition
The effect of antidepressants on body weight is drug-specific rather than class-specific, and is superimposed on the weight effects of the depressive illness itself. Amitriptyline, nortriptyline and other tricyclics commonly produce weight gain of several kilograms through histamine H1 and serotonin 5-HT2C receptor antagonism, which increases appetite and reduces satiety, with anticholinergic and sedative effects contributing to reduced activity; monoamine oxidase inhibitors, particularly phenelzine, are also associated with weight gain. Mirtazapine causes the most consistent and often the largest gain among modern agents, driven by potent H1 blockade and 5-HT2C effects, frequently 2 to 4 kg within six to twelve months and more in some patients. Among selective serotonin reuptake inhibitors, weight change is biphasic: nausea and early anorexia usually cause slight loss during the first weeks, followed by gradual gain with longer term use, and the magnitude differs between agents, with paroxetine showing the greatest risk and sertraline, citalopram and fluoxetine being closer to neutral, although fluoxetine is often weight-neutral or mildly weight-reducing over the first year. Bupropion, a noradrenaline and dopamine reuptake inhibitor, is weight-neutral or produces modest loss and is often selected when weight is a concern, and venlafaxine, desvenlafaxine and duloxetine are generally weight-neutral or mildly weight-reducing. Individual variability is large and unpredictable, so monitoring is more informative than prediction. Clinical management includes recording weight, waist circumference and relevant metabolic parameters before starting and at intervals, avoiding abrupt discontinuation because of discontinuation syndrome and relapse risk, switching to a weight-neutral agent when clinically appropriate, treating associated sleep disturbance and inactivity, and providing structured nutrition and activity support rather than attributing all weight change to behaviour. Where weight gain is significant, the possibility that it is driven substantially by the drug should be stated plainly, and blood glucose and lipids should be checked since weight gain of this kind can unmask insulin resistance.
Key Insight
Why It Matters
Patients taking antidepressants who gain weight often hear advice to eat less, when the medicine itself is part of the cause. Naming the drug effect, checking weight and metabolic markers over time and reviewing the choice with the prescriber is the fairer and more effective conversation.
Sources
Reviewed against standard medical references.
Medically reviewed by
Family Physician & Registered Acupuncturist, Accord Medical Clinic. MBBS (NUS), Graduate Diploma in Family Medicine (NUS), Graduate Diploma in Acupuncture (Singapore College of TCM).
Last reviewed: September 2026
This page is general health education, not medical advice. Whether any treatment is appropriate for you is a decision made in consultation after assessment.
