Monoamine oxidase inhibitors (MAOIs) are a class of drugs that inhibit the activity of one or both monoamine oxidase enzymes: monoamine oxidase A (MAO-A) and monoamine oxidase B (MAO-B). They are best known as effective antidepressants, especially for treatment-resistant depression and atypical depression. They are also used to treat panic disorder, social anxiety disorder, Parkinson's disease, and several other disorders.
Monoamine oxidases (MAO) are a family of enzymes that catalyze the oxidation of monoamines, employing oxygen to clip off their amine group. They are found bound to the outer membrane of mitochondria in most cell types of the body. The first such enzyme was discovered in 1928 by Mary Bernheim in the liver and was named tyramine oxidase. The MAOs belong to the protein family of flavin-containing amine oxidoreductases.
α-Methyltryptamine is a psychedelic, stimulant, and entactogen drug of the tryptamine family. It was originally developed as an antidepressant at Upjohn in the 1960s, and was used briefly as an antidepressant in the Soviet Union under the brand name Indopan or Indopane before being discontinued.
Phenelzine, sold under the brand name Nardil, among others, is a non-selective and irreversible monoamine oxidase inhibitor (MAOI) of the hydrazine family which is primarily used as an antidepressant and anxiolytic to treat depression and anxiety. Along with tranylcypromine and isocarboxazid, phenelzine is one of the few non-selective and irreversible MAOIs still in widespread clinical use.
Myristicin is a naturally occurring compound found in common herbs and spices, such as nutmeg. It is an insecticide, and has been shown to enhance the effectiveness of other insecticides.
Tranylcypromine, sold under the brand name Parnate among others, is a monoamine oxidase inhibitor (MAOI). More specifically, tranylcypromine acts as nonselective and irreversible inhibitor of the enzyme monoamine oxidase (MAO). It is used as an antidepressant and anxiolytic agent in the clinical treatment of mood and anxiety disorders, respectively. It is also effective in the treatment of ADHD.
Tyramine, also known under several other names, is a naturally occurring trace amine derived from the amino acid tyrosine. Tyramine acts as a catecholamine releasing agent. Notably, it is unable to cross the blood-brain barrier, resulting in only non-psychoactive peripheral sympathomimetic effects following ingestion. A hypertensive crisis can result, however, from ingestion of tyramine-rich foods in conjunction with the use of monoamine oxidase inhibitors (MAOIs).
α-Ethyltryptamine, also known as etryptamine, is an entactogen and stimulant drug of the tryptamine family. It was originally developed and marketed as an antidepressant under the brand name Monase by Upjohn in the 1960s before being withdrawn due to toxicity.
Harmala alkaloids are several alkaloids that act as monoamine oxidase inhibitors (MAOIs). These alkaloids are found in the seeds of Peganum harmala, as well as Banisteriopsis caapi (ayahuasca), leaves of tobacco and coffee beans. The alkaloids include harmine, harmaline, harmalol, and their derivatives, which have similar chemical structures, hence the name "harmala alkaloids". These alkaloids are of interest for their use in Amazonian shamanism, where they are derived from other plants. Harmine, once known as telepathine and banisterine, is a naturally occurring beta-carboline alkaloid that is structurally related to harmaline, and also found in the vine Banisteriopsis caapi. Tetrahydroharmine is also found in B. caapi and P. harmala. Dr. Alexander Shulgin has suggested that harmine may be a breakdown product of harmaline. Harmine and harmaline are reversible inhibitors of monoamine oxidase A (RIMAs). They can stimulate the central nervous system by inhibiting the metabolism of monoamine compounds such as serotonin and norepinephrine.
Selegiline, also known as L-deprenyl and sold under the brand names Eldepryl, Zelapar, and Emsam among others, is a medication which is used in the treatment of Parkinson's disease and major depressive disorder. It has also been studied and used off-label for a variety of other indications, but has not been formally approved for any other use. The medication, in the form licensed for depression, has modest effectiveness for this condition that is similar to that of other antidepressants. Selegiline is provided as a swallowed tablet or capsule or an orally disintegrating tablet (ODT) for Parkinson's disease and as a patch applied to skin for depression.
Isocarboxazid is a non-selective, irreversible monoamine oxidase inhibitor (MAOI) of the hydrazine class used as an antidepressant. Along with phenelzine and tranylcypromine, it is one of only three classical MAOIs still available for clinical use in the treatment of psychiatric disorders in the United States, though it is not as commonly employed in comparison to the others.
Clorgiline (INN), or clorgyline (BAN), is a monoamine oxidase inhibitor (MAOI) structurally related to pargyline which is described as an antidepressant. Specifically, it is an irreversible and selective inhibitor of monoamine oxidase A (MAO-A). Clorgiline was never marketed, but it has found use in scientific research. It has been found to bind with high affinity to the σ1 receptor (Ki = 3.2 nM) and with very high affinity to the I2 imidazoline receptor (Ki = 40 pM).
Rasagiline, sold under the brand name Azilect among others, is a medication which is used in the treatment of Parkinson's disease. It is used as a monotherapy to treat symptoms in early Parkinson's disease or as an adjunct therapy in more advanced cases. The drug is taken by mouth.
Pargyline, sold under the brand name Eutonyl among others, is a monoamine oxidase inhibitor (MAOI) medication which has been used to treat hypertension but is no longer marketed. It has also been studied as an antidepressant, but was never licensed for use in the treatment of depression. The drug is taken by mouth.
Pheniprazine, formerly sold under the brand names Catron and Cavodil, is an irreversible and non-selective monoamine oxidase inhibitor (MAOI) of the hydrazine group that was used as an antidepressant to treat depression in the 1960s. It was also used in the treatment of angina pectoris and schizophrenia. Pheniprazine has been largely discontinued due to toxicity concerns such as jaundice, amblyopia, and optic neuritis.
4-Benzylpiperidine is a drug and research chemical used in scientific studies. It acts as a monoamine releasing agent with 20- to 48-fold selectivity for releasing dopamine versus serotonin. It is most efficacious as a releaser of norepinephrine, with an EC50 of 109 nM (DA), 41.4 nM (NE) and 5246 nM (5-HT). It has a fast onset of action and a short duration. It also functions as a monoamine oxidase inhibitor (MAOI) with preference for MAO-A.
Mebanazine is a monoamine oxidase inhibitor (MAOI) of the hydrazine chemical class that was previously used as an antidepressant in the 1960s, but has since been withdrawn due to hepatotoxicity.
Ampyzine, also known as dimethylaminopyrazine or as ampyzine sulfate in the case of the sulfate salt, is a drug described as a "central stimulant" or "CNS stimulant" and "euphoriant". It is said to be a monoamine oxidase inhibitor (MAOI). Ampyzine was first described in the scientific literature by 1960.
Bazinaprine (SR-95,191) is an experimental drug candidate. It is a monoamine oxidase inhibitor (MAOI) which is believed to be useful for the treatment of depression. The drug strongly inhibits type A monoamine oxidase, but only weakly inhibits type B. The effects of the drug are reversible in vivo, but not in vitro. In studies, the chemical has been shown to not interact in vivo with other neurotransmitter or drug receptor sites.
Acetryptine (INN), also known as 5-acetyltryptamine (5-AT), is a drug described as an antihypertensive agent which was never marketed. Structurally, acetryptine is a substituted tryptamine, and is closely related to other substituted tryptamines like serotonin (5-hydroxytryptamine). It was developed in the early 1960s. The binding of acetryptine to serotonin receptors does not seem to have been well-investigated, although it was assessed at the 5-HT1A and 5-HT1D receptors and found to bind to them with high affinity. The drug may also act as a monoamine oxidase inhibitor (MAOI); specifically, as an inhibitor of MAO-A.
