THC is the cannabis compound with the strongest evidence for nausea. Two drugs made from THC, dronabinol and nabilone, hold FDA approval for nausea and vomiting caused by chemotherapy. CBD has thin evidence for nausea in humans. No CBD product carries FDA approval for that use.
FDA-approved THC drugs
Dronabinol (Marinol) and nabilone (Cesamet) received FDA approval in 1985. Dronabinol is synthetic THC. Nabilone is a synthetic compound with a THC-like shape. Both come as oral capsules. Doctors prescribe them when standard antiemetics fail, such as after chemotherapy that causes severe vomiting.
Capsule labels list doses set by body surface area or fixed strengths. Labels also list side effects: drowsiness, dizziness, dry mouth, and mood changes. These drugs can impair driving.
How THC reduces nausea
THC binds CB1 receptors. Those receptors sit in the brainstem and the gut. The brainstem site includes the dorsal vagal complex, a circuit that controls the vomiting reflex. CB1 activation in that circuit dampens the signal that triggers vomiting. Chemotherapy drugs release serotonin, which acts on 5-HT3 receptors and starts the reflex. THC acts downstream of that step.
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CBD and nausea
A 2011 study in the British Journal of Pharmacology found that CBD reduced vomiting in rats. The effect ran through 5-HT1A receptors, not CB1. Human trials on CBD for nausea are few and small. Current evidence does not support CBD alone as a treatment for chemotherapy nausea.
Cannabinoid hyperemesis syndrome
Long-term heavy cannabis use can cause the opposite problem. Cannabinoid hyperemesis syndrome (CHS) brings repeated vomiting, belly pain, and nausea. Symptoms appear after months or years of daily use. Hot showers or baths give short-term relief, which is a hallmark of the condition. The treatment with the best results is stopping cannabis. Some hospital studies report more CHS cases in states with legal sales.
What to check on a product label
- THC content, listed as mg per serving or per capsule.
- CBD content, listed the same way.
- Lab test results for potency, pesticides, heavy metals, and solvents.
- State law. Federal law still lists cannabis as Schedule I.
Questions for a clinician
- Is the nausea from chemotherapy, pregnancy, migraine, or another cause?
- Do standard antiemetics work for me?
- Would a THC drug interact with my other medicines?
Data on smoked or vaped cannabis for nausea is thinner than data on capsules. Trials use oral THC. Smoking delivers THC in minutes, but dose control is poor and smoke irritates the airway.