I see a few good studies mentioned in this forum, but I haven't seen any mention of caffeine or adenosine blockers. Findings from a longitudinal study examining the effects of caffeine found that people who drink a moderate amount of caffeine (or more) per day were less likely to develop Parkinson's disease, or for it to develop later in life. In response to that, several studies were done which strongly suggest that caffeine does indeed slow the progression of Parkinson's disease. Since caffeine works as an adenosine blocker, several studies were done to test the effects of adenosine blockers to slow the progression of Parkinson's. I've read several of these studies, and they all lead to the conclusion that adenosine blockers in general can reduce the amount of l-dopa needed to control Parkinson's, and can slow progression of the disease. All the studies I read have copyrights which expressly forbid posting them to online forums, so I can't post them here. If you're interested, you can search for scholarly articles about adenosine, caffeine and Parkinson's disease.