The risk of Parkinson's was reduced by about 45% among adults who regularly took drugs known as nonsteroidal anti-inflammatory drugs (NSAID) compared to non-users, the Harvard School of Public Health study said on Monday.
These drugs include ibuprofen, indomethacin and naproxen. Even those who took two or more aspirin daily received a measure of protection from a disease which afflicts millions, especially people over the age of 50.
But NSAIDs also carry their own risks from long-term use, especially liver damage.
"There is experimental evidence that NSAIDs are protective for the cells that are selectively destroyed," said study author Dr Honglei Chen of Harvard.
It was not known if taking NSAIDs can benefit people who already have Parkinson's, as is the case with Alzheimer's disease, Chen said. The causes of the two neurological diseases are unknown.
The study, which was published in The Archives of Neurology journal, used data from two studies involving health workers - a 14 year study of 44,000 men, ending in 1990, and an 18 year nurses study with 98,000 women, ending in 1998.
In an accompanying editorial, Dr Mya Schiess of the University of Texas suggested refinements in the study's findings may lead to possible treatments of Parkinson's.
Another report in the same journal projected that the number of Americans afflicted with Alzheimer's disease will triple to 13.2 million by the year 2050 from 4.5 million in 2000, based on an analysis of census data and disease patterns.
The expanding population of those older than 85 are particularly at risk for the mind-robbing disease.
"The large public health challenge is to make these projections obsolete and irrelevant by discovering routes to the prevention of the illness," wrote study author Denis Evans of St Luke's Medical Centre in Chicago.