I'll attempt to answer your questions

Each anti-depressant has a slightly different side-effect profile from one another, but the side effects are similar for closely-related ones. Some are "energizing" (Prozac) while others are more sedating (Zoloft). The "perk you up" ones are more like Prozac, while the "numb you out" ones are more like Zoloft.

Patients with very low energy and motivation sometimes are given the energizing ones, while patients with higher anxiety levels are given the more sedating ones.

Every patient's neurochemistry is different, so Prozac might work well for a friend and completely "disagree" with you or not work at all.

The goal of all anti-depressants is the same: to relieve the core symptoms of depression. Unfortunately at this time, it's a trial-and-error procedure mostly. Some patients can tolerate certain side effects (such as loss of libido) better than other patients.

Two last points: 1- Medication is not for everyone but should at least be considered by patients with moderate to severe depression; and 2- a course in psychopharmacology is really needed to thoroughly explain the drugs, their side effects, and other essential prescribing information.

Hope all that helped a tad.

https://www.ncbi.nlm.nih.gov/pubmed/18494537