Chemotherapy causes nausea in part by damaging cells in the gut lining. The damaged cells release serotonin, which signals to the brain that you might have been poisoned and hence triggers nausea and vomiting with the aim of getting rid of the poison.
The reason the human body is receptive to THC and CBD is that we produce cannabinoids like these naturally and that we have specialized receptors for them. Endocannabinoids (endo meaning internal) are a class of naturally occurring molecules which help control pain, nausea, vomiting, hunger and sleep among many other things.
For example, when we experience an injury, our body produces endocannabinoids in an attempt to dull the pain. These molecules bind to the CB1 receptors in the brain and spinal cord blunting pain signals. Endocannabinoids act like a dimmer switch for our nervous system. When this becomes overreactive, endocannabinoids step in to turn down the volume and restore balance.
research concluded that cannabinoids were more effective than placebo and similar to conventional antiemetics for CINV
Cannabis contains active chemical compounds called phytocannabinoids (plant-based cannabinoids) like THC and CBD. Because their molecular structure closely mimics the endocannabinoids our body produces, they can hijack the CB1 receptors triggering the soothing effect they were meant to produce.
THC and CBD act differently. The former binds with the CB1 receptors in the brain replacing our natural endocannabinoids with a much stronger alternative, causing a "high," altered time perception, increased appetite, and temporary memory disruption. CBD, on the other hand, does not bind to the CB1 receptors, but instead prevents enzymes from breaking down our natural endocannabinoids, thus prolonging the effect. CBD further reduces the production of serotonin, the molecule which originally caused the nausea and vomiting.
To study the effect of cannabis on nausea and vomiting, researchers have tested these phytocannabinoids on rats, a mammal which is unable to vomit, but which exhibits the typical gaping response when exposed to specific flavors, contexts and stimuli. The research has shown how cannabis suppresses conditioned gaping reactions (nausea) in rats in the same way that they suppress vomiting in emetic species.
The 2024 modern landmark trial, Grimison et al., studied the effect of cannabis on humans. The research concluded that cannabinoids were more effective than placebo and similar to conventional antiemetics for CINV. Regardless, patients still tended to prefer them to both placebo and to other antiemetics.
Stephen Dickter CC BY-ND 2.0It has to be noted that for some the side effects are substantial, and critics argue that cannabinoid toxicity (dizziness, dysphoria, hallucinations and paranoia) is unacceptably high. But patients consistently disagree.
The 2024 official position of the American Society of Clinical Oncology states that adults undergoing chemotherapy and suffering from nausea and vomiting can try, in addition to synthetic cannabinoids like dronabinol and nabilone, also other medications containing a 1:1 ratio of the phytocannabinoids’ THC and CBD.
Doctors who prescribe cannabinoids for CINV generally start with a low THC dose (around 2.5 mg) and increase the dosage slowly. Oral products take 30 minutes to 2 hours to act, so people are warned against re-dosing too soon. CBD also inhibits liver enzymes that metabolize some chemotherapy and supportive drugs, so the doctor needs to be aware of this.
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