There is a millennia worth of anecdotal evidence supporting that weed helps with nausea. For reasons scientists continue to explore, smoking weed often provides almost immediate relief to patients experiencing nausea and vomiting. However, there isn't enough research explaining the mechanisms behind this effect. Additionally, there is an association between chronic cannabis use and the development of cyclical vomiting in some users.      

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How Cannabinoids Ease Nausea

The two most abundant cannabinoids in marijuana are tetrahydrocannabinol (THC) and cannabidiol (CBD). These cannabinoids induce medicinal effects in the body through different but synergistic mechanisms.  THC directly engages the endocannabinoid system, a neuromodulatory system consisting of cannabinoid receptors located throughout the body.

CB1 and CBD receptors that transmit messages to the brain, pervade most organ systems.  A high concentration of CB1 receptors exist in the brain and nervous system while CB2 is predominantly found in immune cells with including:

  • The cardiovascular system
  • GI tract
  • Liver
  • Adipose tissue
  • Bone
  • Reproductive system. 

THC stimulates both CB1 and CB2 receptors in ways that reduce inflammation, pain, and nausea, and (at the right dose) enhance mood. Studies have suggested that CBD influences some cannabinoid receptors and might actually increase the effect of THC.

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Mechanistically, THC blocks certain proteins that transport endocannabinoids for further chemical modification hence prolonging the activation of the CB1 receptor. 

Cannabis and Chemotherapy Induced Nausea and Vomiting

One of cannabis’ first uses in modern medicine was for managing cancer-related symptoms, especially chemotherapy-induced nausea and vomiting. A 2019 review in Therapeutic Advances in Medical Oncology confirmed the beneficial role cannabis plays in the care of cancer patients. After evaluating hundreds of peer-reviewed studies on the use of cannabis for the treatment of cancer-related symptoms, Kleckner et al. in the above report concluded the following about cannabis and nausea: 

“There is evidence that cannabis or cannabis-derived products can alleviate chemotherapy-induced nausea and vomiting, and an inhalable form could be better for patients unable to retain oral medications. However, most data are from the 1980s, and cannabis has not been compared with modern anti-emetic regimens.”  
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The problem is that nausea and vomiting are two symptoms that vary in how they manifest during chemotherapy and they occur through different mechanisms.  Modern vomiting controlling treatments are quite effective at preventing vomiting, but are not as effective at controlling nausea

A cannabis spray that reduces nausea and vomiting 

In an interesting study published in 2010, 16 patients on chemotherapy who experienced chemotherapy-induced nausea or vomiting despite standard treatments had a mouth spray administered.

The spray either had THC and CBD or a placebo. Their findings were that those who ingested the spray with the cannabinoids “experienced less nausea and vomiting than those on the placebo.”

Additionally, in 2017, The US National Academies of Sciences, Engineering, and Medicine reported that there is conclusive evidence that oral cannabinoids are effective in the treatment of chemotherapy-induced nausea and vomiting.

Lack of research for cannabis treatment vs standard medicinal treatment

Despite the evidence, it's surprising that there are no studies comparing cannabis and more typical medicinal treatments. This is especially important since the overall cancer death rate has declined, the number of cancer survivors has increased and so has incidence of treatment including chemotherapy. It's critical that medical professionals have clear direction on how to guide their cancer patients as they navigate cannabis as an alternative therapy.

Cannabis and Morning Sickness

One of the most frequently experienced symptoms of pregnancy is morning sickness, or pregnancy-induced nausea and vomiting. Despite the misnomer, it can last all day long and start at any point in the day or during the pregnancy. For most women, morning sickness begins and ends in the first trimester. But some women experience nausea for their entire pregnancy, while others experience an extremely serious sickness called hyperemesis gravidarum, a cyclical vomiting condition that can, if untreated, leave both the mother and unborn child dangerously malnourished and dehydrated.

The increased legal accessibility to cannabis has presented pregnant women with an alternative therapy to treat morning sickness and hyperemesis gravidarum.

A 2019 Drug and Alcohol Dependence study analyzed trends in cannabis use among pregnant women from 2009 to 2016. Using data collected from the Kaiser Permanente Northern California (KPNC) healthcare system, the KPNC research team found that the prevalence of cannabis use among pregnant women has escalated every year.

This increase in cannabis use comes without any clinical evidence supporting the medical use of marijuana during pregnancy. Existing evidence is mixed. Some research shows no contraindication during pregnancy, while other studies show an association between cannabis use and low birth rate and preterm delivery.

The American College of Obstetrics and Gynecology meanwhile says due to the limitations of studies done in regards to cannabis and pregnancy, “...women who are pregnant or contemplating pregnancy should be encouraged to discontinue marijuana use” due to uncertainty about how cannabis could affect pregnancy and a developing fetus. 

Cannabinoid Hyperemesis Syndrome 

A 2017 Journal of Medical Toxicology published a review of literature about the diagnosis, pathophysiology, and treatment of cannabinoid hyperemesis syndrome (CHS), a cyclical vomiting condition associated with the overconsumption of cannabis.  The Colorado-based team of researchers found that a diagnosis of CHS was based on these key markers: 

  • A history of regular cannabis use lasting at least 1 year 
  • Severe nausea and vomiting 
  • Vomiting that occurs in a cyclical pattern that lasts for months 
  • Cessation of symptoms after stopping cannabis use
  • Abdominal pain 
  • Weekly cannabis use 
  • A history of daily cannabis use 
  • Symptom relief from hot baths or showers      

The cause of CHS is unclear. Even more confusing, not all frequent cannabis users develop CHS. While cannabis is implicated in the onset of the condition, Sorenson et al. didn't identify a single theory explaining the relationship between weed and CHS.  Instead, the researchers noted multiple theories including a cannabinoid-caused disruption of the ECS, genetic variations in cannabis users, cannabinoid interactions with CB-1 receptors located in the gastrointestinal tract, and dysregulation of CB-1 receptors throughout the body.

According to Sorenson et al., the only confirmed method of treatment was abstinence from cannabis. CHS is yet another example of the need for more research on cannabis, a plant that can conclusively alleviate the symptoms of nausea and vomiting for most but may also trigger cyclical vomiting in some.