Tozadenant (, ; developmental code names RO4494351 and SYN-115) is an adenosine A<sub>2A</sub> receptor antagonist which was under development for the treatment of Parkinson's disease and liver disorders but was never marketed due to safety concerns. It is taken orally. Tozadenant was under development by Roche, Acorda Therapeutics, and Biotie Therapies. It reached phase 3 clinical trials for Parkinson's disease prior to the discontinuation of its development. The development of tozadenant was discontinued due to findings of agranulocytosis and associated serious adverse effects in clinical trials including five patient deaths.