Under certain conditions or in an overdose setting, several classes of drugs can induce illusions, hallucinations, or delusions. However, one of the hallmark features of hallucinogens or psychedelic agents is their ability to induce states of altered or distorted perception, thought, and mood. Many hallucinogens produce classic sympathomimetic effects; that is, hyperactivity, mydriasis (dilated pupils), hypertension, tachycardia, and hyperthermia. However, the effects vary considerably, depending upon the hallucinogen ingested. Qualitative confirmation by the laboratory that the patient is suffering from hallucinogen intoxication such as marijuana use can be helpful to the clinician. However, the common toxicologic drug screens used by most clinical laboratories do not detect many hallucinogenic agents (such as LSD [lysergic acid diethylamide]). Thus, diagnosis of hallucinogen ingestion and treatment is often based on history of use and physical examination.