Drugs that suppress immune system may protect against Parkinson's: People who take immunosuppressants less likely to develop the disease -- ScienceDaily

Racette and colleagues analyzed Medicare Part D prescription drug
data on 48,295 people diagnosed with Parkinson's in 2009 and 52,324
people never diagnosed with Parkinson's. They identified 26 commonly
prescribed immunosuppressant drugs, representing six classes of
medications. The researchers determined which people in the data set had
been prescribed any of the drugs a year or more before the date of
diagnosis or by a pre-set cutoff date. Prescriptions written in the 12
months before diagnosis or by the cutoff were excluded to rule out any
chance that the prescriptions might have been linked to early signs of
the disease.
The researchers found that people taking drugs in either of two
classes were significantly less likely to develop Parkinson's than those
taking no immunosuppressants. People taking corticosteroids such as
prednisone were 20 percent less likely to be diagnosed with Parkinson's,
while those on inosine monophosphate dehydrogenase (IMDH) inhibitors
were about one-third less likely.

Here's the paper:-

Immunosuppressants and Risk of Parkinson Disease. Annals of Clinical and Translational Neurology, May 31, 2018