Monoamine Oxidase Inhibitors (MAOIs)

The MAOIs were actually the first drugs used to treat depression. While not as popular as they once were, the MAOIs are still useful for people who do not get well enough with one of the other classes of medication or whose depression is severe. Not unlike other antidepressants, the MAOIs increase the amount of chemicals in synapses between brain cells.

However, they do this not by blocking the reuptake pump in transmitting cells, but by blocking the breakdown of a number of neurotransmitters involved in depression via an enzyme, monoamine oxidase, located inside specific neurons. The result is more of the needed chemicals become available for the cells to transmit to other cells and normalize chemical function in the brain. Unfortunately, the MAOIs also block the breakdown of an important amino acid called tyramine.

Tyramine is contained in many foods, especially aged cheese. If people do not severely restrict their tyramine intake while on an MAOI, tyramine rapidly accumulates in the body, leading to a sharp increase in blood pressure which can be fatal. Because MAOIs affect a number of different brain chemicals, they are associated with a number of side effects including orthostatic hypotension (which can make the elderly more prone to falling), weight gain, insomnia and sexual dysfunction.

Used too soon after certain other antidepressant medications are stopped, the MAOIs can cause a serious toxic condition, serotonin syndrome, leading to confusion, agitation and other symptoms. MAOIs are not considered first choice for the majority of depressed people but they are useful in people who have both depression and anxiety, for those who eat and sleep a lot because they are depressed and for those who have not responded well to other antidepressants.

Currently available MAOIs available in Canada to treat depression include phenelzine (Nardil) and tranylcypromine (Parnate). Both agents are very similar in their efficacy and side effect profile.

• Try reading under a bright light and hold book at a distance or wearing reading glasses if blurred vision occurs. Prescribed eye drops may also help.
• Get up slowly if you are lying or sitting down to minimize dizziness.    Use talcum powder if sweating occurs.
• Don't stop the drug abruptly or you may experience headache, excitability and possibly hallucinations.
• Avoid insomnia by taking the last dose of the day no later than 3 p.m.
• If you miss a dose and your prescription requires several doses a day, take the missed dose when you remember it not later than 3 p.m.
• Take dietary restrictions seriously; otherwise, a severe hypertensive reaction could occur. Restricted foods include all mature or aged cheeses; broad beans, meat extracts, dried salted fish, sauerkraut and sausage, especially salami and mortadella. Reactions have also been associated with a number of other foods including pickled herring, sour cream and yogurt, soya sauce, tinned fish and homemade red wine, beer, and sherry.
• Used in moderation, dietary restrictions do not apply to wine or spirits.
• Make sure food is fresh and eaten soon after purchase and avoid any food that may be fermented or possibly

Back to Treatment of Depression