The fact that some result in loss of brown adipose tissue can lead to weight gain. Metformin has been shown to ameliorate this. Interestingly, the alkaloid herbal supplement berberine can also block weight gain. (http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0093310)
atypical anti-psychotic are Dopamine Receptors antagonist, this lead to eat more than normal, and so to weight gain. And there are for a lot of them antagonist of Histamine Receptor, this lead to eat more too.