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MAOI Antidepressants

Monoamine Oxidase Inhibitors are Rarely Used in Depression Any More

Feb 10, 2009 Maija Haavisto

Monoamine oxidase inhibitors are effective antidepressants. Most of them require strict dietary restrictions, but with newer MAOIs they may not be necessary.

MAO inhibitors used to be popular antidepressants due to their efficacy, but they have been largely abandoned because of the serious, life-threatening interactions they can cause with normal foods. Still, they can be very helpful for those who haven't been helped with other antidepressants, especially those with atypical depression.

Mode of Action

The MAOI antidepressants work by blocking the activity of monoamine oxidase, an enzyme which breaks down neurotransmitters like serotonin, norepinephrine (noradrenaline), epinephrine (adrenaline) and dopamine.

There are two types of MAO, MAO-A and MAO-B. Blocking MAO-A mostly increases the brain levels of serotonin, melatonin, norepinephrine and epinephrine and MAO-B the levels of phenylethylamine and dopamine. The majority of MAOI antidepressants block most subtypes, but some are selective for either one.

MAOIs can be either reversible or irreversible. The irreversible ones permanently deactivate monoamine oxidase and even after discontinuing the drug it can take two weeks for the body to replace the enzyme.

Problems and Side Effects

When taking MAOIs, ingesting foods containing the amino acids with tyramine or tyrosine may lead to a life-threatening problem called hypertensive crisis, which means an extreme surge of high blood pressure that can be deadly.

The problem is that many commonly enjoyed foods contain tyramine or tyrosine, including e.g. aged cheeses, wine, coffee, chocolate, avocados, bananas and most fermented and pickled foods from yoghurt to sauerkraut and soy sauce. Depending on the drug and the food, these foods may have to be avoided altogether or only eaten in moderation.

Besides the food interactions, MAOIs should not be combined with most psychiatric drugs, including SSRIs and tricyclic antidepressants. Some opiates, St. John's wort, L-tryptophan, 5-HTP, dextromethorphan, carbamazepine (Tegretol) and cyclobenzaprine (Flexeril) should also be avoided.

There can also be interactions with anticholinergic drugs, antihistamines, levodopa/L-dopa, lithium and even alcohol. As a result one should always consult their doctor before taking any new drugs, prescription or non-prescription, if taking MAOIs.

MAOI Drugs Currently Available

Moclobemide (Manerix) is a reversible MAOI, selective for MAO-A. As a result it is not as prone to diet interactions as most other MAOIs. Besides depression it has been helpful in preventing migraine and tension headaches. It is not available in the U.S, but is sold in Europe, Canada and Australia.

Phenelzine (Nardil) is an irreversible, non-selective MAOI. It also increases the levels of GABA in some parts of the brain similar to anxiolytic drugs, which may explain why it works so well for many people with anxiety. It has also been used in migraine prevention.

Tranylcypromine (Parnate) is a reversible, non-selective MAO inhibitor which is used to treat depression and PTSD. It is less sedative than phenelzine. While other MAOIs may be useful for headaches, tranylcypromine is not recommended for those with headaches.

Isocarboxazid (Marplan) is a non-reversible, non-selective MAO inhibitor used in the treatment of depression, anxiety disorders (including panic disorder and agoraphobia) and bulimia. It is only available in very few countries besides the United States.

Selegiline is an irreversible inhibitor of MAO-B, so it mostly increases brain levels of dopamine and is quite energizing. Like other dopaminergic drugs it has been used in the treatment of Parkinson's disease, but a new transdermal patch (Emsam) has been approved for the treatment of depression.

Emsam is the first antidepressant available as a patch. With it dietary restrictions are usually not considered necessary. Rasagiline (Azilect) is a drug similar to selegiline, but it is not used in depression, only Parkinson's disease.

Some herbs have MAO inhibitor properties. Kava kava (Piper methysticum) is thought to act as a mild MAO-B inhibitor. The popular herb St. John's Wort (Hypericum perforatum) is also a mild MAO inhibitor, though it is also believed to have other antidepressant mechanisms.