eli5 How do antidepressants and other medications cause someone to *gain* weight?

Question

eli5 How do antidepressants and other medications cause someone to *gain* weight?

In: 90

Answer 1

There are several explanation. From my expiriance, mostly by increase in water retention or increase in appetite. There might be some other explanations (insulin, hunger hormones, sex hormones etc.)

Also, some of my patients gain weight on antiallergens (antihistamines). My guess is that it makes them less active due to known effects on sleep cycle and general feeling of tiredness.

All in all, no medication can really make someone gain weight, only food can (Laws of thermodynamics). But it might affect hunger, water consumption/retention, energy expenditure or physical activity.