Cannabis is a psychoactive plant that has been utilized for medicinal and hallucinogenic purposes for hundreds of years.  With the legalization of Cannabis, widespread use, and stronger synthetic preparations, the potential harmful effects of Cannabis are becoming increasingly known, one of which is Cannabinoid Hyperemesis Syndrome.  First described in 2004, Cannabinoid Hyperemesis Syndrome is described as cyclical episodes of nausea, vomiting, and abdominal pain, sometimes associated with autonomic symptoms such as diaphoresis, flushing, piloerection, and tachycardia.  Abdominal pain is described as epigastric or periumbilical.  Curiously, hot showers or baths help relieve symptoms and become instinctual to those suffering from CHS.  To those affected, symptoms of CHS usually present within 24 hours of use, helping to differentiate the disorder from Cannabis Withdrawal Syndrome, and can last up to 2 weeks, despite abstinence of Cannabis during that period.  Mechanism of action remains unclear.  Paradoxically, Cannabis is sometimes used to control nausea and vomiting.  Perhaps at low doses, there is an antiemetic effect, but with stronger synthetic preparations and higher doses, there are pro-emetic effects, at least in some individuals.  Hospitalization is sometimes required for hydration and to help control the nausea and vomiting and for proper GI investigation to assess for other causes.  Typical anti-emetics such Reglan, Compazine and Ondansetron are often ineffective.  Haloperidol, Droperidol, and Capsaicin Cream (in a thin film over the abdomen) have been used with some success during hospitalization to resolve symptoms.  Men are typically more affected than women.  Users often describe frequent Cannabis use, not only daily, but multiple times per day.  Long term abstinence is the definitive treatment.  Repeated trips to the Emergency Department in otherwise healthy adolescents and adults for cyclical nausea and vomiting without other explanation should be the tip off to consider this syndrome. Often a diagnosis of exclusion, it can be considered up front in the right setting.