Monoamine oxidase inhibitors are an older class of antidepressant drugs, also known as MAOIs. They are most often used to treat atypical depression and for smoking cessation. This class of antidepressants is used less often than the other classes because of severe dietary restrictions. There can be fatal interactions with other medications, supplements, and types of food or alcohol.
Depression is thought to be caused by an imbalance of brain chemicals, known as neurotransmitters, that relay signals. Examples of neurotransmitters involved in moods are serotonin and noradrenaline. If there are not enough of these compounds in the body, depression can result. These particular compounds are monoamines, which means they have an NH2 group on them. Monoamines are degraded by an enzyme called monoamine oxidase.
A monoamine oxidase inhibitor acts by preventing the breakdown of monoamines by inhibiting monoamine oxidase. This allows the buildup of the neurotransmitters involved in moods, thereby reversing depression. Monoamine oxidase inhibitors were introduced in the 1950s, but were withdrawn from the market in the United States for a while due to fatal interactions with other substances.
Some foods contain monoamines, such as the amino acid tryptophan or its breakdown product, tyramine. It is critical to avoid foods containing these substances — and certain medications — while taking monoamine oxidase inhibitors, but this was not known when these drugs were first introduced. One should avoid most alcoholic beverages, aged cheeses, pickled herring, fava or broad beans, and liver. People using these drugs should also minimize the amount of chocolate consumed. There is a large list of foods to be avoided when on this type of medication because, for instance, tyramine interacts with the monoamine oxidase inhibitor to cause a large increase in blood pressure, and can cause a stroke.
One must also be careful with medications and dietary supplements, such as St. Johns Wort, as the interactions can be fatal. Both illegal and legal stimulants must also be avoided, these include cold formulas that contain pseudophedrine. The pain medication Demerol®, dextromorphan — a common ingredient in cough syrup — and asthma inhalers, along with numerous other medicines, are also dangerous to use while taking this type of drug. It can be lethal to take the anti-depressant class of selective-serotonin re-uptake inhibitors (SSRIs) at the same time as monoamine oxidase inhibitors. One should allow two weeks to pass before switching between these classes of anti-depressants, and five weeks in the case of Prozac®.
Due to these precautions, monoamine oxidase inhibitors are generally the last choice of anti-depressant to treat depression. They can, however, be a good option for some patients, particularly those with atypical depression and social phobias. With atypical depression, patients frequently have mixed depression and anxiety. Another group of people often helped by these drugs is those who suffer from panic attacks or agoraphobia. This class of anti-depressants is generally not used, however, for cases of severe depression.
There is an advantage to monoamine oxidase inhibitors, in that they do not cause non-suicidal people to become suicidal. This can be a side effect of some of the other classes of anti-depressants. They are, however, a bad choice for potentially suicidal patients, since they could be toxic at high doses and could be used as a method for overdosing. Many people carry an identification card to alert emergency personnel that they are taking a monoamine oxidase inhibitor. These types of drugs should not be used by pregnant women or children under the age of 16.
Commonly prescribed monoamine oxidase inhibitors include phenelzine, which is also know as Nardil®; tranylcypromine, sold as Parnate®; and isocarboxazid, which is also called Marplan®. There is another drug that is worn as a skin patch, which has fewer side effects at low doses. It is selegiline, also known as Emsam®. One must still take precautions when using this drug.
There is a newer class of monoamine oxidase inhibitors known as RIMA — short for reversible inhibitors of monoamine oxidase type-A. This class of MAOIs is reversible, and does not interact with tyramine as strongly, so food interactions are less of a problem. One still should still not eat excessive amounts of foods containing tyramine, and avoid the medications that cause side effects with the older monoamine oxidase inhibitors. These types of drugs are used to treat major depression.