MDMA, commonly known as Ecstasy, has been shown to ameliorate symptoms of Parkinson's in mice. Duke University cell biologists published their findings in the journal Public Library of Science Biology. The researchers tested a variety of amphetamine-related drugs on mice bred to have severe deficiencies of dopamine in the brain. They found that MDMA, more than the others, reduced muscle rigidity, tremor, and impaired movement common with Parkinson's. From the Public Library of Science press release:
Future work will be required to understand how MDMA was able to ameliorate the symptoms of Parkinson's in these mice and to assess the toxicity of MDMA and related compounds in greater detail in the future. However, this study opens the door to a search for compounds related to ecstasy, which may provide a more effective treatment in the later stages of the disease – and hopefully allow patients to perform the simple functions of everyday life independently again.
UPDATE: Thanks to the readers who informed me that in 2001, BBC Two's science program Horizon explored Ecstasy's potential as a Parkinson's treatment. Link