Since we know from various studies that sleep debt (less than 7 hours a night in one study) can lead to weight gain, one factor may be that some of these medicines reduce sleep or change the type of sleep (causing poor quality of sleep that the person may or may not notice). Some people have insomnia as a side effect of antidepressants. This could lead to overeating. Some medicines effect the REM cycle or change the stages of sleep. Both insomnia or sleep type changes could effect hormones.