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 enzyme, Tolcapone increases the amount of levodopa available to the brain, leading to more consistent dopamine levels and improved motor function. This results in longer "on" periods and reduced motor fluctuations in patients with advanced Parkinson’s disease. Due to the risk of liver toxicity, its use is typically reserved for cases where other COMT inhibitors are not effective or tolerated.