There are many different medications that are used to treat depression.
The newer medications like Pristiq incorporate SNRI (serotonin norepinephrine reuptake inhibitor) to target two specific neurotransmitters: serotonin and norepinephrine. Older antidepressants like Prozac, Paxil, Zoloft, Celexa, Effexor and Luvox are SSRI - they only target serotonin receptors.
You have to decide with your doctor which medication is right for you, and you may have to try several different medications before you find the right one for you.
If you are taking things like cocaine, alcohol, marijuana or other street drugs, you need to let your doctor know, because they affect your brain chemistry too, and medications may not be (and most likely are not) appropriate to combine with those other drugs.