By Max Sargent

Cannabis boasts a good safety profile. Thousands of years of use and virtually zero deaths tied to cannabis alone mean users face considerably low risk when using the herb. Most people enjoy cannabis in peace and use the plant to relax, enhance creativity, and socialise. But for a small minority, using cannabis causes some seriously nasty symptoms. Cannabis (or cannabinoid) hyperemesis syndrome (CHS) results in vomiting, pain, and strange, compulsive behaviour.

What Is Cannabis Hyperemesis Syndrome (CHS)?

Revered cannabis scientist Dr Ethan Russo describes CHS as “an enigmatic constellation of signs and symptoms[1]” that show up in some people following heavy and prolonged cannabis use. Medical professionals in Australia first identified the condition in nine patients back in 2004, but researchers eventually traced the first (known) case back to a man who exhibited the symptoms in 1996.

People that experience CHS often use cannabis for years before experiencing any signs of the condition. But eventually, constant exposure to high levels of THC triggers symptoms to emerge. The term “hyperemesis” means “severe or prolonged vomiting”. People with CHS experience nausea and vomiting in a cyclic fashion over several months, to the degree that the condition results in frequent hospitalisation.

But patients can make several trips to the emergency room before receiving a diagnosis, as practitioners frequently misdiagnose CHS as cyclic vomiting syndrome (CVS), a condition often treated with medical cannabis!

With that said, doctors are likely to start identifying the condition much earlier. Some researchers believe CHS goes massively underreported but poses a burgeoning issue. The ever-increasing THC levels in modern cannabis varieties will also likely contribute to the emergence of more frequent cases.

CHS has also put the myth that “cannabis can’t kill you” to rest. At least two deaths have been documented[2] from this toxic reaction to THC.

  • What Are the Symptoms of CHS?

Cannabinoid hyperemesis syndrome symptoms are divided into three key stages.

Prodromal Phase
The prodromal phase marks the period between the initial symptoms and the full-blown development of the condition. The length of these early symptoms[3] varies between patients and can take place over several weeks or even over several years. The symptoms during this phase include:
Early morning nausea
Abdominal pain
Fear of vomiting
Hyperemetic Phase
The hyperemetic phase refers to the point where the symptoms begin to peak. These symptoms include:
Ongoing nausea
Repeated episodes of vomiting
Abdominal pain
Reduced food intake and weight loss
Recovery Phase
The recovery phase begins when a patient with CHS stops using cannabis. The symptoms gradually begin to fade, and patients start to tolerate food normally again. The recovery period lasts from several days to several months.
  • But Doesn’t THC Help To Reduce Nausea and Vomiting?

Many CHS patients are shocked to find that cannabis causes them to vomit. After all, aren’t several cannabis-based medicines used to treat nausea and vomiting?

While true, cannabinoids such as THC display a biphasic dose response, meaning they produce one of two effects based on the amount consumed. Whereas ongoing studies are exploring the antiemetic (drugs that reduce nausea and vomiting) effects of small doses of THC, larger doses are known to promote vomiting.

- Compulsive Bathing: A Strange Behaviour Seen in Most CHS Patients

Vomiting aside, CHS also causes odd behaviour in patients. Many of them find themselves compulsively bathing in hot water. We’re not talking about the occasional dip here. Around 92% of CHS patients report taking frequent hot baths or showers to relieve their symptoms. This technique appears so effective that some patients even report spending most of their day sitting in the tub.

What Causes Cannabis Hyperemesis Syndrome?

We know that large doses of THC can cause vomiting in anyone. But many CHS patients consume the same amount of cannabis as other people that don’t experience these symptoms. So, what’s going on?

Some cannabis users refuse to accept that THC is behind their symptoms, and for good reason. Many depend on medical cannabis to help alleviate certain symptoms, whereas others use the herb recreationally and highly value the effects.

This denial led to a theory that something else must be at play. Some users pointed a finger at the contamination of cannabis flowers, suspecting that residual pesticides underpinned the constant vomiting of CHS. But Dr Russo has refuted this claim, stating that it holds no water. The symptoms of pesticide poisoning don’t correlate with CHS symptoms.

Unfortunately for CHS patients, their toxic reaction to THC likely stems from genetic factors. Dr Russo and colleagues released a paper in July 2021 titled “Cannabis Hyperemesis Syndrome Survey and Genomic Investigation”[4]. The study found five genetic mutations that distinguish CHS patients from other cannabis users that don’t vomit after THC exposure. The team also point to changes in the endocannabinoid system that might underpin the symptoms of the condition. Check out some of these factors below.

What Causes Cannabis Hyperemesis Syndrome?

  • Shifts in the Endocannabinoid System

You've probably heard of the endocannabinoid system (ECS) by now. This system regulates many physiological processes. Researchers have found that CHS patients display the following changes in this vital system.

- Downregulation of CB1 Receptor

The ECS comprises two primary receptor types: CB1 and CB2. The former occurs abundantly throughout the brain and nervous system, and helps to regulate neurotransmitter firing. THC binds to these sites to produce its psychotropic effect. In cases of CHS, researchers have discovered a downregulation of the CB1 receptor in patients following chronic THC use.

- TRPV1 Mutations

The team also found genetic mutations in the TRPV1 receptor. Some researchers label this site as the third cannabinoid receptor, or CB3. Why? Because the primary endocannabinoids—anandamide and 2-AG—and CBD bind to this site.

TRPV1 plays a key role in heat and pain detection, anxiety, and gut motility (the movement of food through the GI tract). Mutations in this receptor likely contribute to the anxiety, pain, and gut issues faced by CHS patients, and it might also explain why many of them often retreat into a hot bath. Activation of TRPV1 may help to reduce nausea and vomiting[5] in CHS.

  • Liver Enzyme Deficiency

Dr Russo and his team also found changes in the liver enzymes of CHS patients. The enzyme CYP2C9 is the main protein responsible for breaking down THC and its potent metabolite 11-hydroxy-THC. Because CHS patients exhibit a deficiency in this enzyme, high levels of THC likely accumulate in the brain, resulting in toxicity.

  • Dopamine Signalling Issues

Mutations in genes that code dopamine receptors also showed up in the study. Substances that stimulate this receptor have an effect on both gut motility and vomiting. The dopamine system also underpins reward-seeking behaviour and addiction. Many CHS patients consume large amounts of cannabis in their daily lives, and many of them continue to return to cannabis despite such unpleasant symptoms. Genetic mutations revolving around dopamine signalling probably play a role here.

  • Does CBD Cause Cannabinoid Hyperemesis Syndrome?

Possibly. While THC seems like the main culprit, researchers state that cannabinoids such as CBD and CBG could conceivably play a role in CHS[6]. Both cannabinoids exhibit pro-emetic (a medicine that induces vomiting) effects at high doses. But we need more research to find out for sure.

How To Diagnose Cannabis Hyperemesis Syndrome?

There are numerous presenting signs[7] that clinicians look for when making a CHS diagnosis, these include:

History of regular cannabis use of over 1 year Severe nausea and vomiting
Vomiting recurring in cyclic patterns over months Symptoms end after a patient stops using cannabis
Compulsive hot bathing or showering Abdominal pain

How To Treat Cannabis Hyperemesis Syndrome?

There are several different treatments available for CHS patients. After they stop consuming cannabis, clinicians may offer the following cannabinoid hyperemesis syndrome treatments:

Capsaicin Topical capsaicin (the spicy molecule in hot peppers) activates TRPV1, and research suggests it may help to reduce nausea and vomiting through this mechanism.
Antipsychotics The antipsychotic medicines haloperidol and olanzapine seem to relieve some of the symptoms of CHS.
Intravenous solutions These help to combat the dehydration associated with the condition.
Pain medications These help to take the edge off of the abdominal pain experienced by 85% of CHS patients.

Is Cannabinoid Hyperemesis Syndrome Permanent?

Unfortunately, it seems like it. Researchers are still untangling CHS, but the findings detailed above point to the genetic basis of the condition. This means that CHS patients almost always experience these symptoms every time they return to the herb. But upon quitting, symptoms should fade.

External Resources:
  1. Cannabinoid Hyperemesis Syndrome Survey and Genomic Investigation
  2. Cannabinoid Hyperemesis Syndrome Survey and Genomic Investigation
  3. Cannabinoid hyperemesis syndrome (CHS)
  4. Cannabinoid Hyperemesis Syndrome Survey and Genomic Investigation
  5. Emerging Role of Aprepitant in Cannabis Hyperemesis Syndrome
  6. Cannabinoid Hyperemesis Syndrome
  7. Cannabinoid Hyperemesis Syndrome Survey and Genomic Investigation
  8. Emerging Role of Aprepitant in Cannabis Hyperemesis Syndrome
This content is for educational purposes only. The information provided is derived from research gathered from external sources.

Are you aged 18 or over?

The content on is only suitable for adults and is reserved for those of legal age.

Ensure you are aware of the laws of your country.

By clicking ENTER, you confirm
you are
18 years or older