Hello pacem,
Yes, I have used citicholine (CDP choline), for years now. It is used in the medical profession to aid recovery from strokes, and helps brain metabolism. It has been reported to reduce the level of levodopa needed, which reduces side effects. I take a low dose of one 250mg tablet per day. Most trials have been done at around 1,000mg per day, but it is expensive. Citicoline reduces the permeability of the blood-brain barrier, which I believe helps parkies. I also take curcumin (which also reduces the permeability of the BBB). I have had PD for 16 years now, and still drive, only take 300mg levodopa per day, can go on demanding holidays, (Tahiti and Crete this year), and just finished laying 80 heavy concrete paving stones as a base for my garden shed. I am now 70 and take the dog a walk daily.
Of course, I can't assign this to any particular supplement, but I am worse when I stop citicoline altogether.
Hope this helps.