Selegiline

Selegiline is a small-molecule monoamine oxidase inhibitor that, at usual therapeutic doses, selectively and irreversibly blocks the B form of the enzyme monoamine oxidase while sparing the A form ^[1]. Chemically it is the levorotatory enantiomer of deprenyl, and it is partly metabolized in the body to levomethamphetamine and levoamphetamine ^[1]. At higher doses this MAO-B selectivity breaks down and the drug also inhibits MAO-A ^[1].

Its first major use was in Parkinson's disease. By inhibiting MAO-B, which breaks down dopamine in the brain, selegiline raises dopamine levels and can be used alone in early disease or as an adjunct to levodopa in more advanced disease ^[1]. In the large DATATOP trial in early, untreated Parkinson's disease, selegiline significantly delayed the point at which patients needed to start levodopa, although whether this reflected a genuine slowing of the disease or simply a symptomatic effect remained unresolved ^[2].

Selegiline is also used for depression. Because taking a monoamine oxidase inhibitor by mouth exposes the gut to the enzyme and creates the risk of a tyramine-induced rise in blood pressure, known as the cheese effect, a transdermal patch was developed that delivers the drug through the skin and largely bypasses this exposure ^[1][3]. Marketed as Emsam, the selegiline transdermal system is approved for major depressive disorder, and at its lowest dose it can be used without the dietary restrictions otherwise required of MAO inhibitors ^[3][4]. It is notable among antidepressants for not causing weight gain or sexual dysfunction ^[4].

Selegiline is available as oral tablets and orally disintegrating tablets for Parkinson's disease and as a transdermal patch for depression ^[1][4]. It is a prescription medication and, unlike stimulant relatives, is generally considered to lack meaningful abuse potential ^[4]. It has also attracted informal interest as a possible cognitive or anti-aging agent, though such uses are not established ^[1].

The principal safety concerns of selegiline stem from its monoamine oxidase inhibition. Combining it with serotonergic drugs such as SSRIs, SNRIs, certain opioids, or dextromethorphan can precipitate serotonin syndrome, and high oral doses taken with tyramine-rich foods or sympathomimetic drugs can cause dangerous rises in blood pressure ^[1][3]. Common milder effects include insomnia, dizziness, nausea, dry mouth, and, with the patch, application-site reactions ^[3][4].

Kept in the low 1 to 5 mg range, selegiline stays selective for MAO-B and is generally well tolerated, with insomnia, dizziness, or nausea the usual mild effects; morning dosing helps sleep. The big caution is the 'cheese effect': as the dose climbs and MAO-A gets inhibited, aged and fermented tyramine-rich foods can trigger a hypertensive reaction, so dose discipline matters. Do not combine it with SSRIs, SNRIs, other MAOIs, tramadol, or dextromethorphan given serotonin syndrome risk; that is the interaction to respect most. It converts to trace amphetamines, so it can feel stimulating. It is a prescription drug for Parkinson's and, as the EMSAM patch, for depression. Not medical advice.

Selegiline is a selective MAO-B inhibitor at low doses, but selectivity is lost at higher oral or transdermal doses, which drives its well-documented interaction warnings. Co-administration with serotonergic agents; SSRIs, SNRIs, tricyclics, meperidine, tramadol, methadone, dextromethorphan, St John's wort, and other MAO inhibitors; is contraindicated because of the risk of serotonin syndrome, and label washout periods apply (for example, five weeks after fluoxetine). Combination with sympathomimetics, pseudoephedrine, or tyramine-rich foods can precipitate hypertensive crisis, so dietary tyramine restriction is advised at higher transdermal doses. It is also contraindicated with other MAOIs and with carbamazepine/oxcarbazepine per the transdermal (Emsam) label. This is research information, not medical advice.

Checking a whole stack? Run it through interactions + stacks.

Selegiline, originally designated E-250 and later known as l-deprenyl, was developed in Hungary in the 1960s by the pharmacologist Jozsef Knoll and colleagues at the Chinoin company, with the molecule synthesized by Zoltan Ecseri. Knoll characterized its defining feature, a selective and irreversible inhibition of monoamine oxidase B, distinguishing it from the nonselective monoamine oxidase inhibitors then in use.

This selectivity meant that at low doses it largely spared monoamine oxidase A, avoiding the dangerous interaction with dietary tyramine known as the cheese effect. Selegiline was introduced for the treatment of Parkinson's disease, where inhibiting the breakdown of dopamine offered clinical benefit, and it is marketed under names such as Eldepryl and Zelapar. In 2006 a transdermal patch formulation, Emsam, was approved by the United States Food and Drug Administration for major depressive disorder.

Selegiline enjoys a durable reputation as a well-understood MAO-B inhibitor with a distinctive place in both neurology and psychiatry. In Parkinson's disease it has long been used to extend dopaminergic tone, and its transdermal patch offered a clever solution to an old problem, delivering enough drug to treat depression through the brain while minimizing exposure in the gut and liver so that, at the lowest patch strength, the traditional tyramine dietary restrictions can be relaxed. Its selectivity at low doses is a genuine advantage over older, nonselective inhibitors. Candor is warranted on two points; that selectivity is lost at higher doses, restoring the need for dietary caution, and its frequently cited neuroprotective properties, while biologically intriguing, have not been confirmed in humans. It remains a respected and still-relevant option.