Tranylcypromine is a monoamine oxidase inhibitor (MAOI) used primarily as an antidepressant for major depressive disorder, particularly atypical depression or cases unresponsive to other treatments like SSRIs or TCAs. It works by irreversibly blocking monoamine oxidase enzymes, increasing levels of neurotransmitters such as serotonin, norepinephrine, and dopamine in the brain, which helps alleviate mood and anxiety symptoms. The drug shows slight preference for MAO-B over MAO-A and has been explored off-label for conditions like treatment-resistant panic disorder, obsessive-compulsive disorder, and even ADHD. Research also investigates its inhibition of histone demethylase LSD1 for potential anticancer applications, though this remains experimental. As a non-hydrazine MAOI, it offers rapid action but requires careful use due to dietary and drug interaction restrictions.