AbstractObjectivesCannabinoid hyperemesis syndrome (CHS) is a clinical condition of cyclic vomiting, nausea, and abdominal pain associated with chronic cannabis use. Despite increased recognition of CHS, there are limited details on cannabis use practices and symptoms over time. Understanding what happens in the period surrounding the emergency department (ED) visit, including any changes in symptoms and cannabis use practices following the visit, can help inform the development of patient‐centered interventions around cannabis use disorder for patients with CHS.MethodsA prospective observational cohort (n = 39) of patients with suspected CHS recruited from the ED at the time of a symptomatic cyclic vomiting episode was followed for 3 months. Disease progression, cannabis use practices, and health care utilization were monitored.ResultsParticipants reported high rates of persistent CHS symptoms (abdominal pain, nausea, or cyclic vomiting) in the 2‐week period immediately following an ED visit with a median duration of 7 days. Cannabis use frequency and quantity were reduced immediately after the ED visit, but most participants returned to pre‐ED visit cannabis use patterns within a few days. Recurrent ED visits for cyclic vomiting were reported by 25% of participants who completed follow‐up during the 3‐month follow‐up period.ConclusionsParticipants continued to have ongoing symptoms after the ED visit, but most managed symptoms on their own and did not return to the ED. Longitudinal studies beyond 3 months are needed to better understand the clinical course of patients with suspected CHS.