The response to treatment is usually good for the first five years or so, but in the longer term these drugs become less effective and higher doses lead to increased side effects. These periods can last from a few minutes to an hour or more. This may be helped by modified release preparations or by giving smaller doses at more frequent intervals. Patients who have mobility problems first thing in the morning or during the night may benefit from a modified release preparation in the evening. Levodopa preparations are best taken after meals to avoid gastro-intestinal side effects.
Nausea is common in the early stages of treatment.
Other side effects include insomnia, depression, excitability, dizziness, tachycardia, arrythmias and reddish discolouration of the urine and other body fluids. These involuntary movements may be controlled by giving smaller doses more often. Vitamin B6 antagonises levodopa unless given with a dopa-decarboxylase inhibitor, so high dose vitamin supplements are best avoided, although the lower amounts found in foods are unlikely to cause problems. Iron may reduce levodopa absorption. Antipsychotics reduce the effect of levodopa and with some antihypertensives there is an enhanced hypotensive action.