Tolcapone (Tasmar - Roche), a dihydroxy-methyl-nitrobenophenone, has been marketed as an adjunct to levodopa/carbidopa (Sinemet, and others) for treatment of Parkinson's disease in both stable patients and those with end-of-dose "wearing off"of levodopa.

Entacapone (Comtan), a catechol-O-methyltransferase (COMT) inhibitor, has been approved by the FDA for adjunctive use with levodopa/carbidopa in patients with Parkinson's disease who have end-of-dose "wearing off"symptoms.

The FDA has approved opicapone (Ongentys – Neurocrine), a peripherally-acting reversible catechol-O-methyltransferase (COMT) inhibitor, for oral use as an adjunct to carbidopa/levodopa in adults with Parkinson’s disease (PD) who experience "off" episodes. It is the third COMT inhibitor to be approved for this indication; tolcapone (Tasmar, and generics) and entacapone (Comtan, and generics) were approved earlier. Opicapone has been available in Europe since 2016.

The FDA has approved istradefylline (Nourianz — Kyowa Kirin), an oral adenosine A_2A receptor antagonist, for use as an adjunct to carbidopa/levodopa in adults with Parkinson's disease (PD) who experience "off" episodes. Istradefylline is the first adenosine A_2A receptor antagonist to be approved in the US; it has been available in Japan since 2013.

The motor symptoms of Parkinson's disease (PD) are caused primarily by degeneration of dopaminergic neurons in the substantia nigra. The nonmotor symptoms of the disease are thought to be caused by degeneration of other neurotransmitter systems. No disease-modifying drugs are available for treatment of PD.

View the Comparison Table: Drugs for Parkinson's Disease