: 66–67   Chinoin received a patent on the drug in 1962 and the compound was first published in the scientific literature in English in 1965.: 67   Work on the biology and effects of E-250 in animals and humans was conducted by a group led by József Knoll at Semmelweis University which was also in Budapest. : 67 

Deprenyl is a racemic compound a mixture of two isomers called enantiomers. Further work determined that the levorotatory enantiomer was a more potent MAO-inhibitor, which was published in 1967, and subsequent work was done with the single enantiomer L-deprenyl. : 67 In 1971, Knoll showed that selegiline selectively inhibits the B-isoform of monoamine oxidase (MAO-B) and proposed that it is unlikely to cause the infamous "cheese effect" (hypertensive crisis resulting from consuming foods containing tyramine) that occurs with non-selective MAO inhibitors. A few years later, two Parkinsons disease researchers based in Vienna, Peter Riederer and Walther Birkmayer, realized that selegiline could be useful in Parkinsons disease. One of their colleagues, Prof. Moussa B.H. Youdim, visited Knoll in Budapest and took selegiline from him to Vienna. In 1975, Birkmayers group published the first paper on the effect of selegiline in Parkinsons disease.In the 1970s there was speculation that it could be useful as an anti-aging drug or aphrodisiac.In 1987 Somerset Pharmaceuticals in New Jersey, which had acquired the US rights to develop selegiline, filed a new drug application (NDA) with the FDA to market the drug for Parkinsons disease in the US.
Side effects
Side effects of the tablet form in conjunction with levodopa include, in decreasing order of frequency, nausea, hallucinations, confusion, depression, loss of balance, insomnia, increased involuntary movements, agitation, slow or irregular heart rate, delusions, hypertension, new or increased angina pectoris, and syncope. Most of the side effects are due to a high dopamine signaling, and can be alleviated by reducing the dose of levodopa.The main side effects of the patch form for depression include application-site reactions, insomnia, diarrhea, and sore throat. The selegiline patch carries a black box warning about a possible increased risk of suicide, especially for young people, as do all antidepressants since 2007. Interactions
Both the oral and patch forms come with strong warnings against combining selegiline with drugs that could produce serotonin syndrome, such as SSRIs and the cough medicine dextromethorphan. Selegiline in combination with the opioid analgesic pethidine is not recommended, as it can lead to severe adverse effects. Several other synthetic opioids such as tramadol and methadone, as well as various triptans, are contraindicated due to potential for serotonin syndrome.Birth control pills containing ethinylestradiol and a progestin increase the bioavailability of selegiline by 10- to 20-fold. High levels can lead to loss of MAO-B selectivity, and selegiline may begin inhibiting MAO-A as well. This increases susceptibility to side effects of non-selective MAOIs, such as tyramine-induced hypertensive crisis and serotonin toxicity when combined with serotonergic medications.Both forms of the drug carry warnings about food restrictions to avoid hypertensive crisis that are associated with MAO inhibitors.