Long-term treatment with levodopa in Parkinson's disease results in the development of motor complications, including drug failure, reduced duration of antiparkinsonian action (wearing off phenomenon), sudden shifts between under-treated and over-treated states (on-off phenomenon), freezing and involuntary movements such as levodopainduced dyskinesia. These motor complications can sometimes be solved with changes in the drug regimen, particularly the addition of dopamine agonists and catechol-O-methyltransferase (COMT) inhibitors and/or changes in levodopa dose, formulation and number of doses. Amantadine and selegiline can also be helpful in reducing motor fluctuations.