In 2002, 8.5 percent of the US civilian noninstitutionalized population had purchased at least one prescription Antidepressant. The currently available classes of Antidepressants include monoamine oxidase inhibitors (MAOIs), tricyclic Antidepressants (TCAs), selective serotonin reuptake inhibitors (SSRIs), serotonin-norepinephrine reuptake inhibitors (SNRIs), novel Antidepressants, and tetracyclic Antidepressants.

MAOIs act by inhibiting monoamine oxidase, a complex enzyme system that metabolizes excess serotonin and epinephrine. It holds the potential of inducing potential life-threatening problems, and therefore cannot be used in patients with congestive cardiac failure or in those with a history of liver disease. It is dangerous to those who are hypersensitive to its ingredients. The important drugs of this class include isocarboxazid (Marplan), moclobemide (Aurorix, Manerix, Moclodura), phenelzine (Nardil), tranylcypromine (Parnate), levo-deprenyl (Selegiline, Eldepryl), and harmala.

Tricyclic Antidepressants (TCAs) act mainly by inhibiting the reuptake of both norepinephrine and serotonin. Though the type of side effects experienced by the patient due to TCAs or MAOIs are many times similar, the frequency of these side effects is much less in the case of TCAs. Thus, TCAs enjoy a better rate of acceptance by the patients. The TCAs of interest in the treatment of depression include amitriptyline (Elavil, Endep, Tryptanol), amoxapine (Asendin, Asendis, Defanyl, Demolox, Moxadil), clomipramine (Anafranil) desipramine (Norpramin, Pertofrane), dothiepin hydrochloride (Thaden, Prothiaden), doxepin (Adapin, Sinequan), imipamine (Tofranil), Iofepramine (Lomont, Gamanil), nortriptyline (Pamelor), protriptyline (Vivactil), and triimipramine (Surmontil).

The SSRIs act by inhibiting the serotonin reuptake, and are considered the most popular, effective and safe prescription medications. The SSRIs used to treat depression include citalopram (Celexa), escitalopram oxalate (Lexapro), fluoxetine (Prozac, Prozac Weekly, Sarafem), fluvoxamine (Luvox), paroxetine (Paxil, Paxil CR), and sertraline (Zoloft). Prozac, a drug of this class, has shown significant success in the treatment of depression and prevention of suicide. It exhibits less potential side effects as compared to TCAs and MAOIs, and is well tolerated.

The currently available SNRIs (desipramine, duloxetine, nefazodone, and venlafaxine) keep both serotonin and norepinephrine at the right level to alleviate depressive symptoms. Nefazodone alleviates anxiety, causes some sedation and positively affects sleep. Venlafaxine (Effexor) has significant anticholinergic effects (dry mouth, blurred vision, urinary hesitancy, and constipation), induces sedation and has potential withdrawal effects.

The drug bupropion (Wellbutrin, Wellbutrin SR) is the most commonly used member of the novel Antidepressant class. It is unique in its efficiency to inhibit the reuptake of dopamine, serotonin and norepinephrine. Maprotiline (Ludiomil) and mirtazapine (Remeron) are the two main drugs from the group of tetracyclic Antidepressant. Mirtazapine acts by increasing the amount of noradrenaline and serotonin, and is of benefit in particular for the treatment of depression accompanied with anxiety, agitation and /or sleep disturbances.

The natural Antidepressants that impress their effectiveness on experts include St. Johns wort (Hypericum perforatum), SAM-e (S-adenosyl-L-methionine), and 5-HTP (5-hydroxytryptophan). Other natural Antidepressants that are in need of research-based studies to prove their efficacy, safety and usability in the treatment of depression include herbs (Ginseng and Ginko), amino acids (l-tyrosine and phenylalanine), and certain nutrients, including B vitamins.