How Anti-Depressants Work: An Informative Layperson’s Guide

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How Anti-Depressants Work: An Informative Layperson’s Guide
It is believed that depression and anxiety are caused by a deficient amount of certain chemicals in the brain that are responsible for a person’s mood. Anti-depressants help combat depression and anxiety (and other mental conditions) by stimulating chemical changes in the brain. These medications correct the chemical imbalance in the brain by boosting the level of certain neurotransmitters, which are brain chemicals responsible for passing messages between brain cells.

Neurotransmitters Affected by Anti-depressants

Depending on the type of anti-depressant, it will affect one, some or all of these neurotransmitters.

  • Serotonin – Plays an important role in many behaviors including mood, sleep, appetite, memory, sexual behaviour and neuroendocrine function.

  • Noradrenaline -Oversees functions in the sympathetic nervous system (e.g. fight or flight response, heart rate, blood pressure, concentration)

  • Dopamine – Involved in functions such as emotion, motivation, pleasure, movement, memory, learning and other roles.

Currently, there are more than 25 anti-depressants on the market that are used to treat a variety of conditions including moderate to severe depression, anxiety, obsessive compulsive disorder and post-traumatic stress disorder.

The complex array of brain chemicals and processes that influence depression varies from person-to-person. This makes it challenging for GPs when trying to determine which anti-depressant is best matched to each patient. Because of this, prescribing antidepressants is often a trial-and-error process until the right anti-depressant is found.

Common Types of Anti-depressants

Most anti-depressants on the market today fall into one of the following categories:

  • SSRI - Selective Serotonin Reuptake Inhibitors are the most commonly prescribed antidepressants. SSRIs increase the amount of Serotonin in the brain by blocking the elimination of Serotonin (which is called Reuptake). Because the removal of this neurotransmitter is inhibited, its level is increased. (Seroxat, Sertraline, Cipramil, and Prozac are all commonly prescribed SSRIs.)

  • TCA - Tricyclic Anti-depressants increase Seratonin, Noradrenaline and Dopamine by also inhibiting the Reuptake process (the removal of these neurotransmitters). TCAs also affect to varying degrees the neurotransmitters, Acetylcholine and Histamine. Because of more possible adverse side effects, these anti-depressants are prescribed less often than SSRIs. TCAs are also effective for treating chronic pain. (Amitryptyline and Prothiaden are both commonly prescribed TCAs.)

  • MAOI - Monoamine Oxidase Inhibitors hinder the action of monoamine oxidase, an enzyme which breaks down monoamine neurotransmitters, thereby increasing the amounts of Serotonin and Noradrenaline. MAOIs are given less often than SSRIs and TCAs because of possible severe side effects and drug interactions when taken with certain food types. MAOIs are often prescribed for depression that is resistant to other depression medications. (Moclobemide is an example of of an MAOI.)

  • SNRI - Serotonin-Noradrenaline Reuptake Inhibitors work very much like SSRIs, except that they increase the neurotransmitter Noradrenaline as well as Serotonin. SSRIs and SNRIs are generally safer than MAOIs and TCAs, causing fewer side effects and drug interactions. (Effexor and Duloxetine are commonly prescribed SNRIs. Note: In high doses, Effexor also slighly increases Dopamine.)

  • DNRIs - Dopamine and Noradrenaline Reuptake Inhibitors affect more Dopamine and Noradrenaline than Serotonin by inhibiting the re-absorption (elimination) of Dopamine and Noradrenaline. (Zyban is a commonly prescribed DNRI.)

Each of these anti-depressants works on different brain areas and affects different processes, which means that there is no single solution that works best for everybody.

Side Effects

Some of the more commonly reported side effects of antidepressants include dry mouth, drowsiness, nausea, changes in appetite and sexual side effects. However, many side effects decrease after the body adjusts to the drug. Usually, more adverse effects are associated with antidepressants that affect more neurotransmitters and larger areas of the brain. If a drug has a more targeted affect on the brain, there are fewer side effects. For example, that is why TCAs have more side effects than SSRIs. Note: Each drug has a profile of its own particular side effects.

Working with Your Doctor

If your physician or psychiatrist prescribes one drug and together you determine with your physician that the prescribed drug is not achieving the desired outcome, your physician may prescribe another type of anti-depressant, or even try combining a few different drugs to help you feel better.

How long will you need to take anti-depressants?
Most people take anti-depressants for at least six months to a year; however, if your doctor determines that you suffer from recurrent depression and/or anxiety (if you've had more than two episodes of depression), your doctor may suggest that you remain on the prescribed anti-depressants for a longer period of time.
As with all medications, if you are taking anti-depressants, do not stop taking them without talking to your doctor. You may become depressed/anxious again. Research shows that 70 percent of patients become depressed/anxious again if they stop taking their anti-depressants too early; yet, the relapse rate falls to less than 15 percent for those who continue taking anti-depressants at least five months after their symptoms begin to lessen.1
When your doctor prescribes an antidepressant, you will want to ask the following questions:

  • Will the anti-depressant prescribed interact with any other drugs you are currently taking?

  • What side effects may you experience? Are these temporary? If not, how long will they last?

  • How long will it take for the drug to work or before you begin to feel better?

  • When is the best time of day to take your medicine?

  • Should the medicine be taken with food or are there any other special instructions?

  • What should you do if you miss a single dose? What should you do if you miss several doses?


  1. From “Making the Antidepressant Decision” by Carol Turkington and Eliot F. Kaplan

About the Author

Kellie Fowler is an award-winning writer and has written for Associated Press, PR Newswire, Fortune 500 companies, newspapers, national business and healthcare magazines. She is regular contributor to Depression Help Resource, a website providing information about antidepressants, treatment options and depression related articles and resources.
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