The diagnosis of cannabis hyperemesis syndrome should be considered for the recurrent attender with nausea, vomiting and abdominal pain. The main diagnostic criteria are long-term (>1 year) of regular cannabis use, normally weekly or daily, and severe cyclical vomiting, often with abdominal pain. One of the differentiators from other cyclical vomiting syndromes is the relief of symptoms with hot showers or baths, as well as resolution with abstinence from cannabis. You obviously want to exclude other life-threatening causes first.
These patients are often troublesome in the ED, upsetting other patients with their dramatic symptoms (some colleagues claim the diagnosis can be made on sound alone), frequent demands to use the shower and being seemingly refractory to standard antiemetic use.
Most management plans include an attempt of standard anti-emetic, but often progress to include another agent with a sedative action. Popular choices include droperidol and chlorpromazine, as they also have anti-emetic properties, as well as diazepam.
This review from 2013 confirms the clinical knowledge that CHS is resistant to most normal antiemetics, and details case reports of successful use of lorazepam in this condition. They conclude that lorazepam could be an agent of choice. Their suggested management also includes IV rehydration, morphine for analgesia and paracetamol for headache.
The limitation in Australian practice is the absence of an IV formulation of lorazepam. Maybe a similar effect could be gained from IV diazepam?