Selegiline (l-deprenyl, Eldepryl® or Anipryl® [veterinary]) is a drug used for the treatment of early-stage Parkinson's disease and senile dementia . In normal clinical doses it is a selective MAO-B inhibitor, however in very large doses (>25mg in a typical adult) it loses its specificity and also inhibits MAO-A. Since it is selective for MAO-B, no special dietary restrictions are needed as with other MAOI drugs. It is sometimes used off-label as a nootropic, as well as for its purported life-extending effects. It is also reported to positively affect libido, particularly in older males. Selegiline is also used (at extremely high dosages relative to humans) in veterinary medicine to treat the symptoms of Cushing's disease and so-called "cognitive dysfunction" in dogs.

Selegiline raises dopamine and phenylethylamine levels in the CNS without directly affecting serotonin or norepinephrine. Selegiline can indirectly raise norepinephrine because dopamine can be catabolized within the brain to norepinephrine, although the extent of this is variable. Selegiline metabolizes partially to an inactive stereoisomer of methamphetamine in vivo in levels that, even if active, are far too low to have any significant effect. However due to this selegiline can cause false positives for amphetamine/methamphetamine on drug tests.

Possibly due to the structural similarity to illegal stimulants, selegiline has been classified as a controlled substance in Japan and thus can only be obtained with a prescription or special government license.