He is the discoverer of both monoamine oxidase (MAO) B inhibitors l-deprenyl (Selegiline) and rasagiline (Azilect) as anti-Parkinson drugs which possess neuroprotective activities.

Youdim upon joining Professor Theodore L Sourkes's laboratory at Allan Memorial Institute, McGill Department of Psychiatry, he began to work on the M.Sc.

One of his most important contributions to science was working with Professor Merton Sandler in London University Post Graduate School to study MAO inhibitors as anti-depressants and anti-Parkinson drugs.

While at Oxford University Medical School, a chance meeting with Professor Peter Riederer resulted in employing the MAO-B inhibitor, l-deprenyl (Later named selegiline) a failed anti depressant, in Parkinson's disease, since the human brain basal ganglia were rich in MAO-B and dopamine.

Together with Prof. John Finberg and Teva Pharmecueitacl AGN1135 was developed as an anti Parkinson's Disease drug called rasagiline (Azilect), approved by FDA in 2006.

His other pioneering contribution is the development of multi-target drugs for treatment of Parkinson's and Alzheimer's diseases possessing iron chleating, monomaine oxidase and cholinesterase inhibitory activities Youdim has published almost nine hundred papers and reviews and edited 45 books in neurochemistry, neuropharmacology, multi-target drug development, and transcriptomics.