text: Rasagiline was tested for efficacy in people with multiple system atrophy in a large randomized, placebo-controlled, double-blind disease-modification trial; the drug failed.
  Teva conducted clinical trials attempting to prove that rasagiline did not just treat symptoms, but was a disease-modifying drug - that it actually prevented the death of the dopaminergic neurons that characterize Parkinson's disease and slowed disease progression.  They conducted two clinical trials, called TEMPO and ADAGIO, to try to prove this.  The FDA advisory committee rejected their claim in 2011, saying that the clinical trial results did not prove that rasagiline was neuroprotective. The main reason was that in one of the trials, the lower dose was effective at slowing progression, but the higher dose was not, and this made no sense in light of standard dose-response pharmacology.