Hilary - Cogentin is an anticholinergic used to control tremor or muscle spasms caused by PD or by other drugs. I don't believe it's widely used in PD these days, since so many other meds have become available. According to the information I have, Cogentin may actually reduce the absorption of Levodopa. When my husband was first diagnosed 17 years ago, the neurologist he was referred to put him on Cogentin. A number of years later when he switched to a PD/Movement Disorder Specialist, the new doctor urged him to get off the Cogentin, although he didn't explain why. Dick found stopping it very difficult to do - each time he tried to withdraw, he became very ill. He was finally able to withdraw by cutting back by 1/4 of a dose at a time over a period of several weeks. Dick did find that the Cogentin helped his tremor initially, but in the long run, was glad he could replace it with more standard PD meds. Does your friend have access to a PD specialist? There are so many newer meds available now that it would be to her benefit to see a doctor who is current on all the advances in PD. Just one person's opinion, for what it's worth. Margie Swindler cg for Dick, 54/17