Because I'm such a stickler on chemistry, I must impress the fact that neurologically, there are different neurotransmitters for different chemicals. It has been clinically proven that neurotransmitters that accept biological chemicals that release dopamine, for instance, (and make the body feel good) close when a person is feeling depressed. So, even when the dopamine is released inside the body from a good work-out, sex, or what have you, the neurortransmitters are closed. Therefore, the end result is the same: depressed. Anti-depressants work by flooding the system with feel-good chemicals, in hope of catching more and more open neurotransmitters. The end result is feeling better and better.

That is the "science" behind the matter. Many new medicines that haven't quite PROVEN this fact are the newer medicines, working towards the same goal. Some meds work toward the same goal in a somewhat different way, but the end result is always the same!