Medicines can cause weight gain in a number of ways, such as by:
- stimulating your appetite, making you feel hungry and eat larger portions and more often
- affecting the way your body stores fat
- slowing your metabolism, which causes your body to burn calories at a slower rate
- making you retain fluid
- affecting your ability to exercise, eg, by causing shortness of breath or making you feel too tired to exercise.
For some medicines, it isn't exactly clear what triggers the weight gain.