I asked my dad the Shrink about this
and he said that there are often side effects to many drugs, but not all people get them. In general, a doc weighs the potential benefits of a medicine with the side effects (and chances of getting them). In your case, your doc felt that the benefits of the Prozac (the brand name of the drug you're taking) outweighed the possible risks, so you should feel assured that he felt the drug had a good chance of working. I'm sure that he will monitor your response (both how you feel as well as any physical side effects) and make whatever changes are necessary to keep you healthy.