Hi bag raiders!
Most psychoactive (i.e. play with your brain) medications can have an effect on weight loss/gain because the way they work effects not just the bits they are aiming for. Unfortunately the way your brain works means that in order to fix a problem in one area, they target neurotransmitters (usually) that are used all over the brain for all kinds of things so they kind of accidentally affect other things, like weight.
Is it possible to lose weight on meds? Yes, it just makes it a tad more difficult, similar to if you had some kind of medical problem that impeded you, like a gammy leg or bad heart stopping you exercising, or hypothyroidism that slowed your metabolism down. They make things more difficult, but you can work around them.
Different people will react differently to different medications (because of different genetic factors and possible slight variations in their particular problem) which is why sometimes it takes a couple of goes to 'get it right' with your meds. It might be that there is another medication that would be better for you, have a chat to your doctor or psychiatrist but my guess is that if it's currently controlling your symptoms they won't be particularly keen to mess with it for the sake of 5kg's.
Keep at it, it may be a bit more difficult but you will get there. Have a chat to your doctor about the weight issue. If it's a common side effect of that particular medication they might be able to make some recommendations about ways to counter the side effect.
Best of luck with it.
35kg lost. (November 2005 - October 2006)
15kg gained again (as at October 2010).
Back to the drawing board - Let's do this thing!
"You can't change the winds, but you can change the sails"
"Reach out and take control of what lands in your lap"