There's no single "best" antidepressant. The doctor prescribes what seems like the most appropriate antidepressant for a specific situation, set of symptoms, and health history.
That being said, a
recently published meta-analysis looking at 117 clinical trials found that after 8 weeks, the most effective antidepressants were escitalopram (Lexapro), mirtazapine (Remeron), sertraline (Zoloft), and venlafaxine (Effexor). The best tolerated (meaning that people were least likely to stop due to side effects) were bupropion (Welbutrin), citalopram (Celexa), escitalopram (Lexapro), and sertraline (Zoloft).
The authors of this analysis (in the journal Lancet) conclude that escitalopram and sertraline seem to be the best choices when starting to treating depression. Citalopram is a slightly less potent form of escitalopram.
If your doctor (or your relative's doctor) prescribes something for depression and it's not escitalopram, sertraline, or citalopram, ask why. Often there's a good reason related to side effects or the particulars of a patient's case -- but it's important to understand why a particular drug was selected for you. If budget is an issue, you might ask about starting with citalopram or sertraline because they have cheaper generic versions.
Once an antidepressant is started, the dosage often needs to be adjusted over time. If the depression hasn't improved after several months on a full dose, it's usually reasonable to give a different antidepressant a trial as well. Note that it can take 4 to 6 weeks for a given antidepressant to take effect in younger people, and sometimes in the elderly the drug must be taken for 12 to 16 weeks before effects are noticed.
If you're prescribed an antidepressant, the most important thing to do is to follow up with your doctor after two months. Together, assess whether things feel different. You may need the dose adjusted upward or a different type of medication. Too often, patients start on an antidepressant but never have sufficient followed up. You're paying for this medication -- you don't want to keep using it if it isn't helping you.
It's critical to follow your doctor's orders about both taking and quitting an antidepressant. Geriatric patients are prone to quitting these drugs because they run out or don't believe they need them, which can cause withdrawal symptoms. Many drugs must be taken for several weeks before effects are noticed.