Rick Simpson Oil (RSO) is a dark, concentrated whole-plant cannabis extract made with a solvent, which many people believe can cure cancer. No randomised trial has tested it, and the few human studies of cannabinoids in cancer used pharmaceutical products, not this oil. This part covers why recovery stories mislead, the documented harms, laboratory testing, the law in Thailand and what a patient or carer can do.
This is Part 2. Part 1: Rick Simpson Oil: What It Is, Where the Claims Came From, and What the Evidence Shows
1. Why Personal Stories Mislead on This Topic
Four filters shape the stories you read online.
- Who posts. A person who gets better writes about it. A person who dies does not. What remains online looks like a success rate, but it is not one.
- Other treatment at the same time. Many stories describe people who were also having surgery, chemotherapy or radiotherapy. The NCI cites a study of 13,180 cancer patients in which 33% used cannabis after their diagnosis.
- Tumours that shrink on their own. This is rare. But among millions of patients it does happen, and the person it happens to credits whatever they were taking at the time.
- No follow-up. Stories are written at a hopeful moment. Cancer outcomes are measured over years.
What you can do: when you read a story, ask four questions: what other treatment did the person have, how long ago was it written, is there a later update, and how many people tried the same thing without posting.
2. Documented Harms
Delaying or refusing standard cancer treatment
This is the most serious harm, and it has firm numbers behind it. Johnson, Park, Gross and Yu published two studies in 2018.
In the Journal of the National Cancer Institute, they compared 281 patients with curable cancers who used alternative medicine instead of standard treatment against 560 similar patients who had standard treatment. They measured the hazard ratio, which shows how much more often death occurred in one group than the other over the same time. The alternative-medicine group died 2.50 times as often overall: 5.68 times for breast cancer, 2.17 times for lung cancer and 4.57 times for bowel (colorectal) cancer.
In JAMA Oncology, the same group studied patients who used complementary medicine alongside standard care. Five-year survival was 82.2% against 86.6%. The authors found the extra deaths were explained by these patients refusing parts of standard treatment much more often.
Interactions with cancer medicines
Antoniou, Bodkin and Ho reviewed cannabinoid drug interactions in the Canadian Medical Association Journal in 2020. The liver breaks down many drugs using a family of enzymes called cytochrome P450 (CYP). THC and CBD are both broken down by the enzyme CYP3A4, and THC also by CYP2C9. CBD slows down the enzymes CYP2C19 and CYP3A4/5, so other drugs that rely on them can build up in the blood. Documented results include:
- with the blood thinner warfarin, a higher INR (the blood test that measures how slowly blood clots) and a higher risk of bleeding;
- a threefold rise in a breakdown product of clobazam (an epilepsy drug);
- a threefold rise in blood levels of tacrolimus (a drug that suppresses the immune system).
Bar-Sela and colleagues published a study in the journal Cancers in 2020. They followed 102 patients with advanced cancer who were receiving immunotherapy (drugs that help the immune system attack the tumour). The 34 who also used cannabis had a shorter median time before the cancer grew again: 3.4 months against 13.1 months. Their median survival was also shorter: 6.4 months against 28.5 months. This was an observational study, so other differences between the groups may explain part of the result. It is still a clear reason to tell the treating team.
Contamination, made stronger by extraction
Extraction concentrates whatever was on the plant. Montoya and colleagues reviewed this in Frontiers in Pharmacology in 2020:
- 84% of the cannabis samples analysed contained pesticide residues, with up to 24 different chemicals in one sample;
- the moulds Aspergillus and Fusarium produce mycotoxins (poisons made by fungi);
- the review describes a lung cancer patient who used cannabis during chemotherapy and died of invasive Aspergillus lung infection 19 days after diagnosis;
- the cannabis plant takes up and stores large amounts of cadmium, lead and mercury from the soil;
- 69% of 84 CBD products tested were wrongly labelled.
Ruchlemer and colleagues made a related point in Supportive Care in Cancer in 2015. Microorganisms carried on cannabis leaves and flowers can cause lung infections in patients with weak immunity, mainly through moulds that are breathed in.
Translator’s note: Thailand’s rainy season and high humidity favour mould on cannabis flowers during growing, drying and storage. Flower that looks clean can still carry Aspergillus. The forum topics Mycotoxins on Cannabis Flower and Pesticide Residues on Cannabis explain the risks and testing.
What you can do: give the treating doctor or hospital pharmacist a written list of every cannabis product taken, with the amounts. Use the forum topic Cannabis Drug Interactions: The List to Take to Your Doctor as a checklist.
3. Laboratory Testing and the Certificate of Analysis
A certificate of analysis (COA) is the report a licensed laboratory issues for one specific batch. As an example of a strict standard, California’s Department of Cannabis Control (United States) requires each batch to be tested in up to nine categories, including cannabinoids, residual solvents, pesticides, heavy metals, microbes and mycotoxins. Six of them matter most for a concentrate.
| Test category | Why it matters for a concentrate |
|---|---|
| Cannabinoids and terpenes | The strength decides how easily someone takes too much |
| Residual solvents | The main hazard of a solvent extract; invisible without a test |
| Pesticides | Extraction concentrates residues instead of removing them |
| Heavy metals | Taken up from the soil, then concentrated by extraction |
| Microbes | Directly dangerous to patients with weak immunity |
| Mycotoxins | Not destroyed by heat, not removed by evaporation |
An oil with no label is especially risky for a patient with weak immunity. None of these problems can be detected by looking, smelling or tasting.
Translator’s note: in Thailand, ask the laboratory whether it is accredited for each test you need, especially residual solvents and mycotoxins, and check that the batch number on the report matches the product. Ask to see the laboratory’s ISO/IEC 17025 accreditation and check that its scope covers these tests on cannabis extracts.
What you can do: do not take any cannabis oil that has no certificate of analysis for its own batch, covering at least the six tests above.
4. The Law in Thailand
Cannabis flower was removed from Thailand’s narcotics list in June 2022. But extracts containing more than 0.2% THC stayed listed as Category 5 narcotics. A concentrated whole-plant extract is far above that limit.
Flower is now controlled by name. The Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568 was signed on 23 June 2025, published in the Royal Gazette on 25 June 2025 and came into force the next day, 26 June 2025. It was issued under the Thai Traditional Medicine Protection Act B.E. 2542 (1999). It makes the flower (ช่อดอกกัญชา) a controlled herb. Flower may be sold for medical purposes only, against a PT 33 (ภ.ท.33) prescription from a recognised practitioner, covering no more than 30 days. Advertising and online sale of flower are prohibited.
Extracts are covered by a separate rule. The Ministerial Regulation on Cannabis or Hemp Extracts B.E. 2569 came into force on 26 April 2026. It allows licences for extracts above 0.2% THC only to Thai juristic persons that are not “foreign” under the Foreign Business Act B.E. 2542, to state agencies, and to the Thai Red Cross Society. The forum topic Thailand’s Two Ministerial Regulations of B.E. 2569 explains both 2026 regulations.
Nothing in either rule makes a home-made or informally supplied concentrate legal. Policy has changed many times since 2022, so check the current position before you act.
Translator’s note: three more verified points apply here.
- The Ministerial Regulation on Controlled Herbs (No. 2) B.E. 2569 came into force on 30 April 2026 and tightened the licence criteria for cannabis flower.
- Processing a controlled herb without a licence is an offence under Section 46 of the 1999 Act. Under Section 78 the penalty is up to 1 year in prison, a fine of up to 20,000 baht, or both.
- The draft Cannabis Control Act is not law yet. The Cabinet approved the draft on 22 September 2026 and sent it to the House of Representatives.
What you can do: before buying or accepting any cannabis oil in Thailand, ask who made it and under which licence. If the answer is “home-made” or “a friend”, it has no legal standing and no quality control.
5. What a Patient or Carer Can Actually Do
Tell the treating team. Cancer doctors are not trying to police what patients take. They want to avoid being surprised by a drug interaction, an infection or a liver blood test they cannot explain.
Ask about interactions. Name every cannabinoid product. Ask whether it affects blood thinners, immunotherapy, or any drug broken down by the CYP enzymes described in the section on interactions above. If the cancer doctor is unsure, ask a hospital pharmacist. A prescribed product has a known content, a tested batch and a professional who is accountable for it. An unlabelled jar has none of these.
Keep the two questions apart. Whether a cannabinoid might help with nausea, appetite, sleep or pain is a reasonable conversation to have with the treating team. Whether an unregulated concentrate should replace or delay cancer treatment is a different question. The survival studies described above show that replacing or delaying treatment led to more deaths. The US NCCIH gives simple advice: do not use cannabis or cannabinoids as a reason to put off seeing a health professional about a medical problem.
Translator’s note: in Thailand, lawful routes include licensed medical cannabis clinics, prescribers authorised to write a PT 33 prescription, and the pharmacist at your hospital. The Government Pharmaceutical Organization (GPO) has made standardised cannabis oil drops in three formulas (THC-dominant, CBD-dominant and 1:1 THC:CBD) for use in hospitals, for example as an add-on for chemotherapy nausea and vomiting and for sleep, appetite and pain in late-stage cancer. Ask the hospital pharmacist which products are available now. The forum topics Medical Cannabis: PT 33 Prescription and When a Patient Declines Cancer Treatment in Favour of Cannabis give more detail.
Share your experience below. If you live with a serious illness, or care for someone who does, and you have looked into this oil, tell us in a reply below: what you were told, what you were promised, and what actually happened. Honest accounts, including the ones that went badly, are the most useful thing this community can give someone searching late at night. A forum thread is not a second medical opinion, and nothing here replaces the doctors, nurses and pharmacists who know your case. Tell them what you are taking.
References
- US National Center for Complementary and Integrative Health (NCCIH): cannabis harms and advice.
- US National Cancer Institute (NCI): professional summary on cannabis and cannabinoids in cancer care.
- Johnson S.B., Park H.S., Gross C.P., Yu J.B. Alternative medicine and survival. Journal of the National Cancer Institute, 2018.
- Johnson S.B., Park H.S., Gross C.P., Yu J.B. Complementary medicine, refusal of conventional treatment and survival. JAMA Oncology, 2018.
- Antoniou T., Bodkin J., Ho J.M. Drug interactions with cannabinoids. Canadian Medical Association Journal, 2020.
- Bar-Sela G. et al. Cannabis use and immunotherapy outcomes in advanced cancer. Cancers, 2020.
- Montoya Z., Conroy M., Vanden Heuvel B.D., Pauli C.S., Park S.-H. Cannabis contaminants limit pharmacological use of cannabidiol. Frontiers in Pharmacology, 2020.
- Ruchlemer R. et al. Inhaled cannabis and infection risk in cancer patients. Supportive Care in Cancer, 2015.
- California Department of Cannabis Control: laboratory testing requirements.
- Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568; Ministerial Regulation on Cannabis or Hemp Extracts B.E. 2569.
This article is part of the Asiannabis Community educational series on extraction and post-harvest processing. It is general information, not medical advice. It is for educational purposes in places where cannabis processing is legally permitted.