What Are the Major Classes of Antidepressants?

Antidepressant Classes

Major Antidepressant Classes
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There are three basic molecules, known chemically as monoamines, which are believed to be involved in mood regulation: dopamine, norepinephrine and serotonin. Antidepressant medications are generally categorized based upon how they affect these three molecules, although the tricyclics are an exception to this rule. The following are the major classes of antidepressants as well as their modes of action and examples of antidepressants belonging to those classes.

Monoamine Oxidase Inhibitors

One of the first classes of antidepressants that were developed was the monoamine oxidase inhibitors (MAOIs).  This antidepressant type, which was discovered in the 1950s, inhibits the action of an enzyme called monoamine oxidase.  Since monoamine oxidase's function is the breakdown of monoamines, its inhibition allows more of the neurotransmitters associated with mood regulation to remain available within the brain.

Drugs like phenelzine (Nardil) and moclobemide (Aurorix, Manerix) are MAOIs.


Another early class of antidepressant is the tricyclics (also known as the heterocyclics), which was also discovered in the 1950s.  Unlike the other classes of antidepressants, this class was named based upon its chemical structure, which is composed of three interconnected rings of atoms.  Tricyclics exert their antidepressant effect by inhibiting nerve cells from reabsorbing serotonin and norepinephrine, which allows more of these substances to be available for use in the brain.

Amitriptyline (Elavil) and desipramine (Norpramin) are examples of antidepressants found in this class.

Selective Serotonin Reuptake Inhibitors

Selective Serotonin Reuptake Inhibitors (SSRIs) work by inhibiting the reuptake of serotonin, allowing more of it to remain available.  The SSRIs were the first class of drugs that were intentionally developed as antidepressants rather than their antidepressant effects being discovered by chance.

  They were developed beginning in the 1970s.

Drugs like citalopram (Celexa) and paroxetine (Paxil, Seroxat) belong to this class of antidepressant.

Serotonin and Norepinephrine Reuptake Inhibitors (SNRIs)

SNRIs aid depression in a similar way to the SSRIs except that they also inhibit the reuptake of norepinephrine in addition to serotonin.  The first SNRI was FDA-approved in December 1993.

Examples of SNRIs include desvenlafaxine (Pristiq) and venlafaxine (Effexor).

Other Mechanisms of Action

There are also other fairly new antidepressants which do not fit into any of the above categories.  Some of these include:  buproprion (Wellbutrin), maprotiline, mirtazapine (Remeron), reboxetine (Edronax, Vestra), trazodone (Desyrel), and vilazodone (Viibryd).

As more antidepressants are developed, these antidepressants may begin to develop into their own groupings of antidepressants or they may remain as standalone antidepressants.  For the time being, however, they remain unique in their modes of action.


Bloom, Floyd E.  "Antidepressant."  Enclyclopedia Brttannica.  Encyclopedia Britannica, Inc.  Accessed:  September 3, 2015.

"Drugs, Diseases and Procedures : Drugs, OTC and Herbals: Psychiatrics." Medscape Reference. WebMD LLC. 2013. Accessed: September 3, 2015.

Omudhome, Ogbu.  "Venlafaxine, Effexor XR."  MedicineNet.com.  MedicineNet, Inc.  Last reviewed:  By Charles Patrick Davis, MD on February 27, 2015.  Accessed:  September 3, 2015.

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