The common belief is that the intake of even large quantities of cannabinoids is harmless. However, subjects with acute cannabinoid intoxication are present more and more frequently in emergency departments (EDs) or clinics. They present a vast array of symptoms, including nausea, cyclical vomiting, agitation, short-term memory loss, cognitive deficits, psychosis, seizures, and arrhythmias. In addition, symptoms associated with the sympathetic system activation, such as mydriasis, hypertension, and tachycardia, are often described.