There is an older category of antidepressant currently used only for people who don't respond well to all the alternatives. This category called MAOI's, or monoamine oxidase inhibitors. MAOI's have lifethreatening interactions with the other antidepressants, as well as with a number of common foods and other drugs. Because these drugs are rarely used, I'm not going to say any more about them. The current theory about depression is that it is caused by an imbalance of neurotransmitters in the brain.
Neurotransmitters are chemicals that allow electrical impulses to flow between nerves.
No one knows whether this imbalance is initially caused by traumatic or sorrowful events, or whether it is a genetic problem like high blood pressure, or both. There are clinicians who believe that antidepressants are best used as a temporary treatment along with psychotherapy, and others who think long-term treatment is the right approach. What matters, of course, is what works for you. This is a new category of drug, generally both safer and more effective than older antidepressants. Drugs in this category are considered the first choices for mild to moderate depression, and include Prozak, Paxil and Zoloft.