Might be a good time to investigate this. Available OTC in US. I think I recall Ron Hutton as using long term as well. Several clinical trials (doses to 1200 mg/day) on Medline with zero side effects other than the DK noted below and corrected with lower dose of Ldopa.

2: Clin Ther. 1988;10(6):664-71.

Clinical trial on the use of cytidine diphosphate choline in Parkinson's
disease.

Cubells JM, Hernando C.

Department of Neurosurgery, Centro Ramon y Cajal, Madrid, Spain.

Thirty patients with Parkinson's disease, treated with levodopa for the past few
years, concomitantly received 500 mg of cytidine diphosphate choline (CDPC)
daily for 30 days. Significant improvements in some of the neurologic signs and
in several electrophysiologic parameters measuring the traction reflex and the
active contraction were observed. A greater stability of therapeutic response
between doses of levodopa was also seen, although the incidence of dyskinesia
increased. In a second stage of CDPC treatment, also lasting 30 days, the dose
of levodopa was reduced by one-third, and the incidence of dyskinesia dropped to
its previous level, but the therapeutic response remained stable. Addition of
CDPC produced significant increases in plasma concentrations of dopa and
homovanillic acid, with no modifications in tyrosine or 3-O-methyldopa
concentrations. A significant increase in the number of lymphocytic dopaminergic
receptors also occurred.

PMID: 3064905 [PubMed - indexed for MEDLINE]