Trials in the 1970s and early 1980s showed that cannabinoids controlled chemotherapy-induced nausea and vomiting better than the anti-nausea medicines of that time. Two synthetic cannabinoid medicines, nabilone and dronabinol, were approved in the United States in 1985. Since then, newer drugs have transformed nausea care. Cannabinoids have moved into a backup role.
This part explains that change and what current cancer-care guidelines recommend. It also covers safety points for patients and carers and the Thai rules. It ends with notes for licensed growers whose flower may reach patients.
Do not change any anti-nausea medicine because of this article. The cancer care team (the oncology team) plans nausea control around the specific chemotherapy regimen. The plan depends on how strongly that regimen tends to cause vomiting. If nausea is not under control, tell the team. Do not swap in anything on your own. In Thailand, cannabis flower is a controlled herb. It may be sold only against a PT 33 prescription, for a maximum of 30 days.
This is Part 2. Part 1: Chemotherapy-Induced Nausea and Vomiting: The Indication That Made Cannabinoids a Licensed Medicine — and Where It Stands Now
1. How Anti-Nausea Care Changed After the 1980s
Chemotherapy nausea has three phases. The acute phase comes within about 24 hours and is driven mainly by serotonin released in the gut. The delayed phase lasts from about 24 hours to several days and is driven mainly by a brain messenger called substance P. The anticipatory phase is a learned reaction before the next cycle, and it follows poor control in earlier cycles.
Two new classes of medicine arrived after the cannabinoid trials had been run:
- 5-HT3 receptor antagonists block the serotonin signal from the gut. Ondansetron was the first, and others followed.
- NK1 receptor antagonists block substance P at its neurokinin-1 (NK1) receptors in the brain. Aprepitant was the first, and others followed.
These are usually given together with a corticosteroid, a type of steroid medicine. Olanzapine, an antipsychotic medicine, has since become a further standard option.
So cannabinoids beat drugs around 1980 that a patient would not receive today. This does not make the old trials wrong. It changes what their result means now. Cannabinoids went from “better than what we have” to “an option when what we have does not work”.
What to do: before you apply the result of an old trial today, look up its year and the drug it was compared with.
2. Where Current Guidelines Place Cannabinoids
Two US bodies publish the cancer-care guidelines cited most often:
- NCCN (National Comprehensive Cancer Network) is an alliance of US cancer centres.
- ASCO (American Society of Clinical Oncology) is the main US professional society of cancer doctors.
The two terms below describe nausea that standard drugs have not controlled:
- Breakthrough nausea and vomiting gets through despite preventive drugs.
- Refractory nausea and vomiting does not respond to standard treatment.
The NCCN Clinical Practice Guidelines in Oncology: Antiemesis list dronabinol among the options for breakthrough or refractory nausea and vomiting. NCCN revises these guidelines often, so check the current version.
ASCO updated its anti-nausea guideline in 2017. It recommends the FDA-approved cannabinoids, dronabinol or nabilone, for nausea and vomiting that resists standard drugs. It found the evidence too weak to recommend medical marijuana in this setting. “Medical marijuana” here means cannabis plant products. ASCO updated the anti-nausea guideline again in 2020.
All of these positions are second-line or later. They apply only after standard preventive treatment has not been enough. They do not replace it.
The 2024 change
In 2024 ASCO published a separate guideline on cannabis and cannabinoids in adults with cancer. It covers adults with refractory chemotherapy nausea and vomiting whose preventive treatment already follows the guidelines. These patients may add one of three options:
- dronabinol;
- nabilone;
- a quality-controlled oral extract with THC and CBD in a 1:1 ratio.
THC (tetrahydrocannabinol) is the main intoxicating compound in cannabis. CBD (cannabidiol) is a non-intoxicating cannabinoid. Any of these options is added to the regular anti-nausea drugs, not used in their place. ASCO rates the strength of this recommendation as weak.
The main trial behind the extract option was published by Grimison and colleagues in Annals of Oncology in 2020. It was an early-stage (phase II), randomised, placebo-controlled crossover trial. All patients had refractory chemotherapy nausea and vomiting. In some cycles they took capsules of THC 2.5 mg and CBD 2.5 mg. In other cycles they took a dummy capsule (placebo).
- Complete response rose from 14% on placebo to 25% on THC:CBD. Complete response is the trial’s main success measure: no vomiting and no rescue medicine from 0 to 120 hours after chemotherapy.
- 31% of participants reported moderate or severe cannabinoid-related side effects, such as sedation, dizziness or disorientation.
- Most participants preferred THC:CBD to placebo.
What to do: if nausea continues despite the standard drugs, ask the oncology team whether one of the guideline add-ons suits the patient. The add-ons are dronabinol, nabilone or a quality-controlled 1:1 THC:CBD oral extract. The team can check the option against the patient’s other drugs and the chemotherapy plan.
3. Which Products the Evidence Covers
The ranking of evidence by product type has not changed. The evidence supports pharmaceutical cannabinoids. It also supports quality-controlled oral extracts with a defined, measured composition.
For this use, the evidence is weakest for smoked or inhaled cannabis and for unregulated flower. No guideline recommendation rests on these products.
What to do: before you trust a product claim about chemotherapy nausea, check which product it is. The evidence covers dronabinol, nabilone, or an oral extract with a stated THC:CBD content and a batch test certificate. No guideline supports flower for smoking.
4. Two Opposite Mistakes When Reading This Evidence
Saying too much: claiming that cannabis is a proven anti-nausea medicine for chemotherapy patients in general. The evidence supports only specific cannabinoid products, used as add-ons for refractory cases. These are the two licensed synthetic compounds and, since ASCO 2024, quality-controlled oral THC:CBD extracts.
Saying too little: claiming that cannabinoids have no evidence-backed role in cancer care. They do have one, here, in guidelines, as a second-line option. Almost no other claim made for cannabis has that much support.
Both mistakes are common. People often make the second one when they react against the first.
What to do: when you post or answer a question about this on the forum, name the exact product and the exact patient group. For example, write “dronabinol as an add-on for refractory chemotherapy nausea”, not “cannabis helps chemo patients”.
5. Practical Points for Patients and Carers
Tell the oncology team when nausea is not controlled
Nausea that is not controlled can be treated, and the team still has several options. It can act only if it knows. Poor control in one cycle makes the next cycle harder, because it can lead to anticipatory nausea.
What to do: keep a simple daily note of nausea and vomiting episodes for each cycle and show it to the team at the next visit. The note shows the team which phase is not covered.
Do not substitute or add anything on your own
Adding or swapping a product on your own carries two risks. The patient can lose the nausea control they already have, and the new product can interact with other drugs. The liver breaks down cannabinoids using a group of enzymes called cytochrome P450. Cancer patients usually take several drugs that the same enzymes clear. See Cannabis Drug Interactions: The List to Take to Your Doctor.
Immunotherapy is one specific reason the team must know. These drugs help the immune system attack the cancer. Taha and colleagues (The Oncologist, 2019) looked back at the records of 140 patients treated with nivolumab, an immunotherapy drug. A study that looks back at records like this (retrospective and observational) can show a link but cannot prove cause.
- The response rate was 15.9% among cannabis users and 37.5% among non-users. The response rate is the share of patients whose tumours shrank.
- There was no significant difference in progression-free survival, the time before the cancer grows. There was also no significant difference in overall survival.
- The authors stressed that forward-looking (prospective) studies are needed.
This does not prove harm. It is still reason enough to tell the team rather than guess.
What to do: take a written list of everything the patient uses to every oncology appointment. Include cannabis products and herbal medicines. The team can then check for interactions before they cause a problem.
Contamination matters more for these patients than for almost anyone else
Chemotherapy often weakens the immune system, which doctors call being immunocompromised. Unregulated cannabis carries documented risks of moulds and bacteria. Inhaled routes are the greatest concern.
What to do: use only products from a regulated channel with batch testing. Ask to see the test certificate.
Know about cannabinoid hyperemesis syndrome
In this condition, regular cannabis use itself causes repeated cycles of vomiting. Hot showers typically bring temporary relief. More cannabis does not help. The syndrome resolves only when cannabis use stops.
In a patient who is already vomiting from chemotherapy, this syndrome is easy to miss. The natural reaction is to take more cannabis, and that makes it worse.
What to do: if a regular cannabis user has repeated bouts of vomiting that ease in a hot shower, tell the doctor about the cannabis use.
6. In Thailand
The Department of Medical Services (DMS) of the Ministry of Public Health publishes guidance on the medical use of cannabis. Its 4th revised edition (January 2021) lists chemotherapy nausea and vomiting among the conditions where cannabis products are considered beneficial. The guidance has been revised since then. The latest edition we found is the 6th revision (2024), so check the current edition.
That is the guidance’s highest evidence group. It also includes conditions such as refractory epilepsy, spasticity (muscle stiffness) in multiple sclerosis and neuropathic (nerve) pain. This placement fits the international guidelines above. It does not make cannabis a first-choice anti-nausea medicine. Any use belongs inside the oncology team’s plan.
Cannabis flower itself is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568, in force since 26 June 2025. It may be sold only against a PT 33 prescription, for a maximum of 30 days. Advertising and online sale of flower are prohibited. For the prescription rules, see Medical Cannabis: What the Term Means, What the Evidence Supports, and Thailand’s PT 33.
Whether flower can be prescribed is one question. Whether dronabinol or nabilone is registered and available in Thailand is a separate one. We could not confirm whether either drug is registered with the Thai FDA. A foreign approval is not a Thai registration.
What to do: do not assume. Ask the treating oncologist or the hospital pharmacy whether dronabinol or nabilone is available. If neither is available, ask which add-on option the team uses for nausea that persists.
7. Notes for Licensed Growers Whose Flower May Reach Patients
Translator’s note: chemotherapy patients are among the most vulnerable people your product could reach, because their immune systems are often weak. Thai conditions raise the mould risk. Rooms reach 30–35 °C, humidity is high in the rainy season, and power cuts can stop dehumidifiers and air conditioning during drying.
- Test every batch for moulds, bacteria and mycotoxins at a laboratory before it leaves the farm. Then you know whether the batch is safe for weak immune systems, and you have proof for the buyer. Ask the lab which accreditation it holds for each test.
- Log the drying and storage room temperature and humidity every day, and record every power cut and how long it lasted. If something goes wrong, you can trace which batch was exposed and retest it.
- Keep your records to the GACP standard (Good Agricultural and Collection Practice). Each batch can then be traced from planting to sale.
- Do not market flower as a treatment for chemotherapy nausea. Advertising flower is prohibited in Thailand. No guideline supports flower for this use either.
If you or someone you care for has been through chemotherapy in Thailand, please share your experience below this topic. Was nausea control discussed before the first cycle, or only after it became a problem? The evidence says the first cycle shapes how the rest go. Members’ reports will show how often that conversation happens in Thai hospitals.
References (Part 2)
- 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.
- 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 (check the current version). Guidelines Detail
- 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
The historical trials (Chan 1987, Dalzell 1986) are listed in Part 1.
Asiannabis Community educational article. It is general information, not medical advice. It is not a reason to change any anti-nausea treatment. The treating oncology team plans nausea control during chemotherapy.