This is where cannabinoid medicine actually started. Not with cancer cures or wellness claims, but with a specific, measurable, miserable problem — patients vomiting through chemotherapy — where trials in the 1970s and 80s showed a cannabinoid outperforming the antiemetics of the day. That work produced the first cannabinoid drug approvals anywhere. What happened next is the part that gets left out.
This is not a reason to change any antiemetic. Nausea control during chemotherapy is planned by the oncology team around the specific regimen’s emetogenic risk. If nausea is not controlled, the answer is to tell the team — not to substitute anything. In Thailand cannabis flower is a controlled herb dispensed on prescription form PT 33 by an authorised practitioner.
1. Why This Indication Is Different From the Rest
Almost everything else discussed under “medical cannabis” sits somewhere on a spectrum from plausible to unproven. This one is different in a specific and checkable way: it produced licensed medicines, through the ordinary regulatory process, forty years ago, and it still appears in mainstream oncology guidelines today.
It is also a clean example of the distinction this forum returns to constantly. Controlling nausea is symptom management. It says nothing whatever about the tumour. A treatment that lets someone keep food down through a chemotherapy cycle is doing something genuinely valuable and entirely different from treating the cancer — and the value is real precisely because the claim is modest. For the broader cancer discussion, see forum topic 1308.
Appetite loss and cachexia are a related but separate indication, with a different mechanism and its own evidence base, and are not covered here.
2. What Chemotherapy-Induced Nausea and Vomiting Actually Is
CINV is not one phenomenon, and treatments differ across its phases.
| Phase | Timing | Principal mechanism |
|---|---|---|
| Acute | Within roughly 24 hours of chemotherapy | Serotonin (5-HT3) released from gut enterochromaffin cells, signalling via vagal afferents to the brainstem |
| Delayed | From about 24 hours up to several days | Substance P acting at neurokinin-1 (NK1) receptors centrally |
| Anticipatory | Before the next cycle begins | A learned, conditioned response after poorly controlled earlier cycles |
Two implications follow, and both matter more than any drug choice. Different phases respond to different drug classes, so one antiemetic is not interchangeable with another. And anticipatory nausea is created by inadequate control of earlier cycles — which makes getting the first cycle right the single most effective intervention in the whole area.
Cannabinoid receptors are present in the brainstem regions that coordinate vomiting, including the dorsal vagal complex, which is the proposed mechanistic basis for a cannabinoid antiemetic effect. It is a different pathway from the serotonin and substance P routes, and that difference may explain why a cannabinoid sometimes helps when those drugs have not — a plausible explanation, not a proven one.
3. The Historical Trials
The trials that established the effect were conducted in the 1970s and early 1980s, at a time when the available antiemetics included prochlorperazine and metoclopramide, and when control of chemotherapy nausea was frequently poor enough that patients abandoned treatment.
Several trials of that era reported cannabinoids outperforming the older antiemetics, including in children. In children, the published comparisons mostly tested nabilone, not oral THC. In a randomised, double-blind crossover trial in 30 children, retching and vomiting improved in 70% of nabilone cycles versus 30% of prochlorperazine cycles, with more dizziness, drowsiness and mood change on nabilone (Chan et al., Pediatrics, 1987). A smaller crossover trial found nabilone reduced vomiting and nausea more than domperidone, again with more somnolence and dizziness (Dalzell et al., Archives of Disease in Childhood, 1986). Trials of that period were sufficient to support regulatory approval.
4. The Approvals
Nabilone, a synthetic cannabinoid analogue, was approved in Canada in the early 1980s and by the FDA in 1985. Dronabinol, synthetic delta-9-THC in an oral capsule, received FDA approval in 1985 for chemotherapy-induced nausea and vomiting in patients who have not responded to conventional antiemetics. A second indication, anorexia associated with weight loss in AIDS, was added in 1992.
Neither drug was licensed as a first-line antiemetic. Both are single synthetic compounds at a defined oral dose. Neither is cannabis, and their approvals do not extend to cannabis. Our separate article on approved cannabinoid medicines covers the full profiles of dronabinol and nabilone.
5. What Happened Next — the Part Usually Omitted
Between the 1980s approvals and today, antiemetic care was transformed by two drug classes that did not exist when the cannabinoid trials were run: the 5-HT3 receptor antagonists (ondansetron and its successors), and the NK1 receptor antagonists (aprepitant and its successors), typically combined with a corticosteroid. Olanzapine has since become a further standard option.
The comparators that cannabinoids beat around 1980 are not the comparators a patient would receive today. That does not retrospectively invalidate the old trials — it relocates the finding. Cannabinoids went from “better than what we have” to “an option when what we have does not work.”
That is exactly where guidelines put them. The NCCN Clinical Practice Guidelines in Oncology: Antiemesis (Version 2.2025) list dronabinol among the options for breakthrough or refractory nausea and vomiting. NCCN versions are revised often, so check the current one. ASCO’s antiemetic guideline update (2017) recommends the FDA-approved cannabinoids dronabinol or nabilone for nausea and vomiting resistant to standard antiemetics, and found the evidence insufficient to recommend medical marijuana in this setting. ASCO updated its antiemetic guideline again in 2020. All of these are second-line or later positions, after standard prophylaxis has proved inadequate — not replacements for it.
The picture moved further in 2024. ASCO’s guideline on cannabis and cannabinoids in adults with cancer (2024) states that adults with refractory CINV despite guideline-concordant prophylaxis may add dronabinol, nabilone, or a quality-controlled oral 1:1 THC:CBD extract to their antiemetic regimen, as an add-on rather than a replacement. ASCO rates the strength of this recommendation as weak. The main trial behind the extract option is a randomised, placebo-controlled crossover trial of oral THC 2.5 mg/CBD 2.5 mg capsules in patients with refractory CINV (Grimison et al., Annals of Oncology, 2020). Complete response rose from 14% on placebo to 25% on THC:CBD. Moderate or severe cannabinoid-related side effects such as sedation, dizziness or disorientation were reported by 31% of participants, and most preferred THC:CBD to placebo.
What has not changed is the hierarchy of evidence. The evidence supports pharmaceutical cannabinoids and quality-controlled oral extracts of defined composition. For smoked, inhaled or unregulated flower, the evidence in this indication remains the weakest, and no guideline recommendation rests on it.
6. Reading This Honestly, In Both Directions
The overstatement to avoid: that cannabis is a proven antiemetic for chemotherapy patients generally. What is supported is specific cannabinoid products — two licensed synthetic compounds and, since ASCO 2024, quality-controlled oral THC:CBD extracts — as add-ons for refractory cases.
The understatement to avoid: that cannabinoids have no evidence-supported role in oncology. They do, here, in guidelines, as second-line therapy — which is more than can be said for almost any other claim made for cannabis.
Both errors are common, and the second is often committed by people reacting against the first.
7. Practical Points for Patients and Carers
Tell the oncology team if nausea is not controlled. That is a treatable problem with several remaining options, and the team can only act on it if they know. Poorly controlled nausea in one cycle makes the next cycle harder through anticipatory nausea.
Do not substitute. Adding or swapping anything on your own risks both losing the control you have and creating an interaction. Cannabinoids are metabolised by the cytochrome P450 system, and cancer patients are typically on several drugs cleared by the same enzymes. Immunotherapy is a specific reason for the team to know. In a retrospective, observational study of 140 patients treated with nivolumab, the response rate was 15.9% among cannabis users versus 37.5% among non-users, with no significant difference in progression-free or overall survival (Taha et al., The Oncologist, 2019). The authors stressed that prospective studies are needed. This does not prove harm, but it is reason enough to tell the team rather than guess.
Contamination matters here more than in almost any other patient group. Chemotherapy patients are frequently immunocompromised, and unregulated cannabis carries documented risks of moulds and bacteria — with inhaled routes the greatest concern. Anything used should come through a regulated channel with batch testing.
Know about cannabinoid hyperemesis syndrome. There is a condition in which regular cannabis use itself causes cyclical vomiting, characteristically relieved temporarily by hot showers, and which does not respond to more cannabis — it resolves only on stopping. In a patient already vomiting for another reason, it is easy to miss, and the natural response of increasing intake makes it worse.
8. In Thailand
The point most relevant here: the Department of Medical Services’ guidance on the medical use of cannabis lists chemotherapy-induced nausea and vomiting among the conditions where cannabis products are considered beneficial. That places CINV in the guidance’s highest evidence group, alongside conditions such as refractory epilepsy, spasticity in multiple sclerosis and neuropathic pain. It is consistent with the international guidelines above. It does not make cannabis a first-line antiemetic, and any use belongs within the oncology team’s plan.
Cannabis flower itself remains a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568, dispensed only on form PT 33 — see topic 1358 for the prescription rules.
Whether dronabinol or nabilone are registered and available in Thailand is a separate regulatory question from whether cannabis flower is prescribable. Check with the treating oncologist or hospital pharmacy rather than assuming. A foreign approval is not a Thai registration.
If you or someone you care for went through chemotherapy in Thailand: was nausea control discussed before the first cycle, or only after it became a problem? The evidence says the first cycle is the one that determines how the rest go, and how routinely that conversation happens here is worth knowing.
References
- US FDA. Marinol (dronabinol) capsules, prescribing information. https://www.accessdata.fda.gov/drugsatfda_docs/label/2026/018651s036lbl.pdf
- US FDA. Cesamet (nabilone) capsules, prescribing information.
- Chan HS et al. Nabilone versus prochlorperazine for control of cancer chemotherapy-induced emesis in children: a double-blind, crossover trial. Pediatrics 1987;79(6):946-952. pubmed.ncbi.nlm.nih.gov
- Dalzell AM et al. Nabilone: an alternative antiemetic for cancer chemotherapy. Arch Dis Child 1986;61(5):502-505. Nabilone: an alternative antiemetic for cancer chemotherapy - PMC
- Hesketh PJ et al. Antiemetics: American Society of Clinical Oncology Clinical Practice Guideline Update. J Clin Oncol 2017.
- Hesketh PJ et al. Antiemetics: ASCO Guideline Update. J Clin Oncol 2020;38(24):2782-2797. pubmed.ncbi.nlm.nih.gov
- Braun IM et al. Cannabis and Cannabinoids in Adults With Cancer: ASCO Guideline. J Clin Oncol 2024;42(13):1575-1593. pubmed.ncbi.nlm.nih.gov
- NCCN Clinical Practice Guidelines in Oncology: Antiemesis, Version 2.2025. nccn.org
- Grimison P et al. Oral THC:CBD cannabis extract for refractory chemotherapy-induced nausea and vomiting: a randomised, placebo-controlled, phase II crossover trial. Ann Oncol 2020;31(11):1553-1560. doi:10.1016/j.annonc.2020.07.020
- Taha T et al. Cannabis Impacts Tumor Response Rate to Nivolumab in Patients with Advanced Malignancies. Oncologist 2019;24(4):549-554. pubmed.ncbi.nlm.nih.gov
- Department of Medical Services, Ministry of Public Health. คำแนะนำการใช้กัญชาทางการแพทย์ (Guidance on the medical use of cannabis). https://cpg.dms.go.th
Asiannabis Community educational article. It is general information, not medical advice, and it is not a basis for changing any antiemetic regimen. Nausea control during chemotherapy is planned by the treating oncology team.