Cannabis, nausea and vomiting: how THC may affect the vomiting reflex

Why do we become nauseated or vomit?

Vomiting is a protective reflex coordinated by networks in the brainstem. Signals reach these networks from the gastrointestinal tract, the bloodstream, the vestibular system, higher brain centers and the vagus nerve. Chemotherapy can strongly activate several of these pathways. Nausea and actual vomiting are related but different outcomes; preventing vomiting does not always remove the distress of nausea.

Serotonin and current antiemetic medicines

Some chemotherapy drugs stimulate serotonin release from cells in the gut. Serotonin acts on 5-HT3 receptors and helps transmit signals to the brain. This is why 5-HT3 antagonists such as ondansetron are widely used. Modern regimens can also include NK1 antagonists and other medicines, selected according to the cancer treatment and the individual patient.

Where does the endocannabinoid system enter?

CB1 receptors participate in neural networks that regulate nausea and vomiting. THC can activate cannabinoid signaling and suppress some emetic signals. The biological mechanism makes therapeutic investigation reasonable, but a response in a receptor pathway is not by itself a recommendation to consume cannabis.

Dronabinol and nabilone: cannabinoid medicines, not smoked cannabis

Dronabinol is a pharmaceutical form of delta-9-THC and nabilone is a synthetic THC-related compound. Both have been used for chemotherapy-induced nausea and vomiting when conventional antiemetics have not provided adequate relief. A standardized medicine with a known dose must not be equated with smoking a cannabis plant or taking an unstandardized extract.

Why old studies cannot settle today’s treatment choices

Older randomized studies sometimes found cannabinoids more effective than placebo or than the antiemetics available at the time. Many trials preceded current combination antiemetic regimens. Results against medicines used decades ago do not establish superiority over modern care. More recent reviews still need to account for this change in comparator and study quality.

What do oncology guidelines say?

The 2024 ASCO guideline discusses certain cannabinoid preparations as a possible addition in selected cases of refractory chemotherapy-induced nausea and vomiting despite guideline-concordant antiemetics. This is not an endorsement of cannabis as a routine substitute for standard prevention or as a treatment for every type of nausea. The NCI likewise distinguishes regulated cannabinoid medicines from evidence on variable cannabis products.

Appetite, quality of life and treatment goals

THC may stimulate appetite. Yet feeling hungrier is not the same as demonstrating durable weight gain or improved nutritional outcomes. In oncology care the relevant measures include eating, hydration, body weight, functional status, symptoms and overall quality of life.

Risks and the paradox of cannabinoid hyperemesis

Cannabinoids can cause drowsiness, dizziness, changes in perception, anxiety, confusion or hypotension. Adverse effects may increase with dose or interacting medicines. Chronic frequent cannabis use can also cause cannabinoid hyperemesis syndrome (CHS), characterized by recurrent episodes of nausea and vomiting. A substance can therefore reduce vomiting in one context and contribute to it in another.

Different causes of nausea need different evaluation

Pregnancy, migraine, infection, gastrointestinal disease, medicines and metabolic disorders can all cause nausea. Evidence from chemotherapy-induced nausea and vomiting should not be generalized to these conditions, and cannabis should not be used to treat nausea during pregnancy. Persistent or severe symptoms require appropriate medical assessment.

Bottom line

Specific cannabinoid medicines have an established, limited place in selected chemotherapy-related nausea and vomiting. In current oncology guidance, certain preparations may be considered as add-on treatment when standard antiemetics provide inadequate relief. Product, dose, interactions, side effects and patient goals all matter. No change to prescribed oncology or antiemetic care should be made without the treating team.

Read original Hebrew article ↗

Scientific sources cited by the Hebrew original

1. National Cancer Institute: Cannabis and Cannabinoids – Antiemetic Effects.
   Read source ↗
2. NCI: Nausea and Vomiting Related to Cancer Treatment.
   Read source ↗
3. ASCO Guideline: Cannabis and Cannabinoids in Adults With Cancer.
   Read source ↗
4. Efficacy of Cannabinoids for the Prophylaxis of Chemotherapy-Induced Nausea and Vomiting: Systematic Review and Meta-analysis, 2025.
   Read source ↗