Tolcapone is primarily used as an adjunct treatment for Parkinson’s disease. It enhances the effectiveness of levodopa therapy by inhibiting the COMT (catechol-O-methyltransferase) enzyme, which breaks down levodopa in the body. By blocking this breakdown, Tolcapone increases the amount of levodopa that reaches the brain, leading to more consistent dopamine levels and improved motor control in patients. This results in reduced "off" periods—times when Parkinson’s symptoms re-emerge between doses of medication. Due to potential liver toxicity, its use requires regular liver function monitoring, but it remains a valuable option for patients with fluctuating responses to standard levodopa/carbidopa regimens.