Anticholinergic (eg akineton and levodopa) drugs are still used by some PD patients and several OTC drugs contains anticholinergic properties, particularly the antihistamines and some other ingredients in OTC cough and cold medication
The anticholinergic effects of these OTC drugs may then produce additive effects with anticholinergics prescribed for PD and lead to toxicity. Symptoms of this adverse interaction may include urinary retention, memory impairment, constipation and impaired near vision.

There have been isolated reports of patients taking levodopa and decongestants together who developed hypertensive crises. Therefore, the use of decongestants such as ephedrine, pseudoephedrine and phenylephrine especially in patients taking Eldepryl and a levodopa combination, should be approached with caution.