An idiosyncratic drug reaction that involves acute involuntary muscle movements and spasms. Although any muscle group in the body can be involved, the most common symptoms are torticollis, facial grimacing, and body arching. Approxi mately 3%–10% of patients exposed to conventional antipsychotics, especially high-potency agents such as haloperidol (HALDOL), will experience an acute dystonic reaction. The movements typically occur at a time when the blood level of medication is dropping.