My son gained twenty pounds in one month on Risperdal. Most psychiatric medications are not weight neutral...most mood stabilizers and antipsychotics cause such a huge appetite increase that you can't control yourself. I'm an adult and gained eighty pounds on Paroxetene (I lost it, but I know folks who never can stop eating). My son has been off medications for five years now, did not have a he appetite before medications, but still overeats now. I often wonder if it effected his metabolism or appetite forever as he is still quite overweight.
It's something to take into consideration, if this is an issue with you. I believe the biggest weight gainers (I used to know the list, but this was a long time ago so I'm putting the drugs in any order): Risperdal, Zyprexa, Depakote, Risperdal, Lithium. I know some huge anti-depressant weight gainers are Paxil/Paroxetine, Remeron, Trazadene, Amitriptylene (I gained 60 on this one).