noisette:
I can't speak for the population as a whole, but my brief experience with antidepressants added 25 pounds for an approximate 20% gain in total weight. I later found out that my experience is not uncommon - though my doctor didn't think it was a problem. That 25 pounds has been far harder to lose than the 35 pounds I gained with my first pregnancy and the 40 pounds I gained with the second - even though I was 39 when I had my second child (age does affect metabolism).
I know antidepressants are an important tool for many people - but my experience was very negative. At the risk of sounding like Tom Cruise, I can only wonder how many modern health problems are exacerbated by the increasing use of these drugs.
My oldest daughter went on antidepressants because of severe clinical depression with suicidal tendencies. It was scary. They worked for her. (Along with very critical therapy.) She is medication free and functioning just fine today. But, I'm not sure she'd be alive without them.
In addition, she lost about 35 lbs when she went on them, though she wasn't trying to diet (we had enough issues to deal with just then.) She maintains a normal weight today.
Asside from ancidotal evidence, now that most antidepressants are not recommended for teens, the teen suicide rate is up sharply everywhere.
Yes, for some people antidepressants don't work. For the majority of people with clinical depression they are a miracle. The real problem is our lack of psychiatric care. When a patient is put on these medicines, they should probably be monitored by trained psycharitrists in an in-patient setting until its certain the drug is doing what its supposed to. Antidepressants casually prescribed by a family practice doctor or internists are probably a very bad idea. Brain drugs are serious business.