The FDA has required that the labels of all carbidopa/levodopa-containing products (Crexont, Dhivy, Duopa, Rytary, Sinemet, Sinemet CR, Stalevo, Vyalev) include a warning about the risk of vitamin B6 (pyridoxine) deficiency and vitamin B6 deficiency-related seizures associated with their use. The combination of carbidopa/levodopa is the most effective treatment for the motor symptoms of Parkinson's disease and recent evidence favors its early use.

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.