These criteria require that patients have taken a serotonergic drug and have one of the following: Muscle hypertonia Spontaneous clonus Tremor plus hyperreflexia Ocular or inducible clonus, plus either agitation, diaphoresis, or temperature > 38° C Systemic infections, drug or alcohol withdrawal syndromes, and toxicity caused by sympathomimetic or anticholinergic drugs should also be considered in the differential diagnosis.