What's the difference between CVS and CHS?
Cyclic vomiting syndrome (CVS) and cannabinoid hyperemesis syndrome (CHS) are both disorders of gut-brain interaction (DGBI), a group of conditions where the signaling between the gut and the brain is disordered. The core difference is cause. CHS is driven by prolonged heavy cannabis use and resolves when that use stops. CVS is not caused by cannabis and does not resolve by quitting it.
Both belong to the same neighborhood of gastroduodenal DGBI, and both produce the same headline feature: discrete, stereotyped episodes of intense nausea and vomiting, separated by intervals where you feel essentially normal. If you are living inside one of these attacks, the two are close to impossible to tell apart on symptoms alone. That is exactly why the distinction gets missed, and why it is worth understanding before you or a clinician settle on an answer.
Why do they look so similar?
They overlap because they share almost every visible feature. Both cause recurrent, stereotyped bouts of relentless vomiting with well intervals in between. Both often start in a predictable way and follow a predictable arc. And here is the part that surprises people: both can produce that strange, specific relief from hot showers or baths. Same picture, different engine.
The hot-water behavior is the clearest example of how the surface can mislead. For years, compulsive hot bathing was treated as a near-signature of CHS. It is common in CHS, but it also shows up in cyclic vomiting syndrome, so it cannot separate the two by itself. When a patient describes standing in a scalding shower for an hour to get relief, that tells you something real about their physiology, but it does not tell you which of these two conditions is behind it.
The other reason they blur together is human, not biological. Many people with CVS use cannabis, frequently to control the very nausea their episodes cause. So a person can genuinely have CVS and also be a regular cannabis user, which makes the case look like cannabinoid hyperemesis syndrome on a first pass. The cannabis is present, but it is a coping tool, not the cause.
How do doctors tell them apart?
The separation comes from three things: an honest cannabis-use history, the migraine connection, and how the body responds to specific interventions. CHS follows heavy, sustained cannabis use, roughly the pattern the Rome criteria describe, and clears with real cessation. CVS travels with migraine and responds well to migraine-type prevention. Those response patterns are the tell.
Start with the cannabis history, told straight. The Rome criteria frame CHS as vomiting in the setting of prolonged, high-frequency cannabis use, on the order of using for at least a year, at least four days a week or fifteen-plus doses a week. That is not a moral threshold, it is a clinical one. The diagnosis of CHS is not confirmed until the picture also resolves with sustained cessation, meaning something like six months off cannabis or three typical episode-cycles clean. That is the actual test.
Next, the migraine link. CVS is strongly tied to a personal or family history of migraine, and that connection is more than trivia. It points toward a shared underlying wiring, and it predicts what will help. CVS tends to respond well to preventive treatment from the migraine playbook, including tricyclic antidepressants used at preventive doses. CHS, by contrast, tends to respond poorly to those same tricyclics. So a clean improvement on migraine-type prevention argues for CVS, and a clean resolution after quitting cannabis argues for CHS.
Does a positive cannabis test settle it?
No. A positive cannabis test does not prove CHS, and it cannot separate the two conditions on its own. Cannabis metabolites linger in the body for a month or more after use, so a positive result only confirms that cannabis is present, which is already true for many people with CVS. The test tells you about exposure, not causation.
This is where a lot of cases go wrong. A clinician sees vomiting plus a positive cannabis screen and closes the file on CHS. But a person with genuine CVS who uses cannabis for nausea will produce exactly that same result. The test cannot distinguish "cannabis is causing this" from "this person happens to use cannabis." Only the pattern over time can do that: whether the episodes actually stop when cannabis is fully removed, and whether migraine-type prevention helps.
That is why the honest resolution is behavioral, not chemical. A candid use history, and when it is appropriate a supervised trial of stopping cannabis, is usually what separates the two. This is a clinician-guided process for a reason. Stopping is only informative if it is complete and sustained long enough to matter, and someone needs to be watching the pattern with you and helping you manage symptoms while you do it.
Why does it matter which one you have?
It matters because the two conditions point toward different long-term paths. If it is CHS, the single most effective intervention is sustained cannabis cessation, and staying on cannabis means staying sick. If it is CVS, quitting cannabis will not fix the underlying problem, and the productive move is preventive treatment aimed at the migraine-type biology driving it. Chasing the wrong one costs you time and relief.
The stakes are not just theoretical. Someone told they have CHS who actually has CVS may quit cannabis, see no improvement, and be left with no plan and a lot of frustration. Someone with true CHS who keeps using because the diagnosis was never made plainly will keep cycling through the same brutal attacks. Getting the label right is what unlocks the right plan.
One thing both conditions share: they are managed supportively during an acute attack, and rehydration is the priority. Standard antiemetics like ondansetron often work poorly in both, which is another reason the two get confused and another reason the acute setting is about stabilizing you, not sorting out the underlying diagnosis. The diagnostic work happens later, in the calmer intervals.
What to do
- Be honest about your cannabis use with your clinician, including how much and how often and for how long. This is the single most useful piece of information for telling these two apart, and it is not a judgment.
- Track your own history and pattern: whether you or close family have migraines, and how your episodes actually run, from the first warning sign to the well interval afterward.
- If CHS is on the table, talk with your clinician about a supervised cannabis-cessation trial that is complete and long enough to be informative, roughly several months rather than several days.
- If the picture points toward CVS, ask specifically about migraine-type prevention, including whether a tricyclic at a preventive dose is appropriate for you.
- Protect your hydration during attacks and know the red-flag signs above, so a bad episode does not become a medical emergency.
- Keep working the problem with a clinician over time. The answer usually comes from the pattern across several episodes, not from a single visit or a single test.
These two conditions wear the same face, but they do not have the same fix, and the difference between them is knowable. An honest history and some patience are usually what get you there.