Weight gain is an often overlooked side effect of many drugs. Some stimulate the appetite or slow the body's metabolism. Others cause fluid retention or enough drowsiness to reduce physical activity and thus trigger weight gain.
Those effects can often be rapid and significant. Children and teenagers starting antipsychotic medication, for example, added an average of about 10 to 19 pounds after taking the pills for nearly 11 weeks, a 2009 study found.
So before starting a new drug, ask your doctor or pharmacist about its possible effect on weight. Exercising more and paying extra attention to diet might help minimize the problem. If you find yourself putting on pounds while taking a medication, ask your doctor about switching to a lower dose or different drug. (Many of the following drugs are also available as generics.)
http://www.washingtonpost.com/wp-dyn/content/article/2010/03/22/AR2010032202843.html