An adult who understands their situation has the right to refuse cancer treatment, including to use cannabis instead. Published studies show that people with curable cancers who refuse standard treatment die sooner. Both facts are true. The person who has to weigh them is usually frightened and has little time to decide.
This part explains the right to refuse, what the survival studies found, and how a careful decision to refuse is made. Part 2 covers decisions about children, what Thai law says about giving medical advice online, and what is safe to post.
This article is not medical advice and not legal advice. It does not recommend accepting or declining any treatment. It explains what the published outcome data shows and the general legal principles. It also covers the position of anyone who gives advice. Almost nobody asks about that last point, and it is the one most likely to end badly. If you face this decision, talk to your oncology team (the doctors and nurses treating your cancer). For legal questions, talk to a qualified lawyer in your country.
1. Three Separate Questions
Discussions of this subject usually turn into arguments that go nowhere. That happens because people answer three different questions as if they were one.
- May a competent adult refuse treatment? This is a question of law and ethics. In most countries it is settled, and the answer is yes.
- What happens to people who make this choice? This is a question of evidence. Published data exists.
- Where does the person who encouraged the refusal stand? This is a legal question. Its answer is different from the answer to question 1. Part 2 covers it.
Mixing these questions produces two common bad arguments. The first is: “It’s my body, so the data doesn’t apply to me.” This treats a right as if it changed the likely outcome. It does not.
The second is: “The data is bad, so you shouldn’t be allowed to choose.” This makes the opposite mistake. A poor likely outcome does not remove the right. Both arguments fail for the same reason: they treat a right and a prediction as the same thing.
What to do: when you read or join a discussion on this subject, first work out which of the three questions is being answered. Then answer only that one. This stops the discussion from turning into an argument where nobody is answering the same question.
2. The Adult’s Right to Refuse
Modern medicine works on informed consent: a patient agrees to a treatment after being told its benefits, risks and alternatives. The other side of this is informed refusal. A person who is able to agree is also able to say no.
In most legal systems, an adult with decision-making capacity may refuse a treatment even if refusing is expected to lead to death. The right holds even if other people think the reasons are mistaken or irrational. It also holds if the reasons rest on beliefs other people do not share.
Some countries use a common-law system, where much of the law comes from court decisions. England is one example. There, treating a competent adult without consent is generally a battery, meaning unlawful physical contact. This applies however helpful the treatment would have been.
Capacity decides whether the right applies
Decision-making capacity means the ability to make one particular decision at one particular time. A well-known test comes from the United Kingdom’s Mental Capacity Act 2005. It asks whether the person can do four things:
- understand the information relevant to the decision;
- retain that information long enough to decide;
- weigh the information to reach a decision;
- communicate the decision.
Under that Act, adults are presumed to have capacity. Disagreeing with the doctor is not evidence that a person lacks capacity. Other countries word the test differently, but most share the same basic ideas.
Capacity applies to one decision at a time. A person may have capacity for one decision and not for another. Capacity can also change with the illness, with medicines and with pain.
What Thai law says
In Thailand, the right written into law is narrower. Section 12 of the National Health Act B.E. 2550 lets a person make an advance directive, also called a living will. This is a written statement, made in advance, about care the person does not want.
Under Section 12, a person may refuse health services that only prolong the final stage of life. They may also refuse care in order to end severe suffering from illness. A Ministerial Regulation of B.E. 2553 sets out the procedure. Health staff who follow a valid directive are not liable for doing so.
Section 12 is about the end of life. On its own wording, it does not cover a decision to decline curative treatment (treatment aimed at curing the cancer).
Thailand’s wider principle of informed consent and informed refusal appears in the Declaration of Patient’s Rights and Duties. The Medical Council of Thailand issued it in 2015 together with other health professional councils. It gives patients these rights:
- to receive enough information before deciding whether to accept treatment, except in an emergency;
- to ask for a second opinion from another health professional who is not treating them;
- for patients under 18, the parents or legal guardian use these rights for them.
The Declaration is a professional standard. It is not an Act of Parliament. Thai legal commentators note that it sets out broad principles, not a detailed legal procedure.
What follows from this
Some patients have understood the prognosis (the expected course of the disease) with and without treatment, and still decline. That patient has used a right. They have not made an error that someone needs to correct.
Doctors in that situation do not have to agree with the decision. They do have to keep offering care and make it easy for the patient to come back.
What to do if you are the patient: ask your doctor to explain the expected outcome with treatment and without it. That way your choice rests on facts, not on fear or guesswork. If you want to put your end-of-life wishes in writing, ask your hospital how it handles a Section 12 directive. A written directive helps make sure your wishes are followed if you can no longer speak for yourself.
Translator’s note: this section covers general principles and Thai law only. Other Southeast Asian countries have their own rules on refusing treatment and on advance directives, and this article does not summarise them. If you live outside Thailand, ask a lawyer in your own country before relying on any of the points above.
3. What the Survival Data Shows
A person using the right to refuse is entitled to accurate information about what that choice costs.
The most-cited outcome studies were published in 2018 by a US research team at Yale School of Medicine, led by Skyler Johnson. They used US National Cancer Database records of patients with curable (non-metastatic) breast, prostate, lung or colorectal cancer. They compared two groups:
- Alternative medicine: patients who used non-standard remedies instead of standard cancer treatment. This group had markedly worse survival.
- Complementary medicine: patients who used non-standard remedies alongside standard treatment. This group also had more deaths. The extra deaths were explained by one thing: these patients refused parts of standard treatment more often.
The measurable harm is linked to refusing treatment, not to using the remedy.
These are observational studies. Researchers recorded what patients chose and what happened to them. They did not assign the choices at random, so other differences between the groups may explain part of the result. The studies also covered alternative medicine in general, not cannabis specifically.
A separate observational study looked at patients with advanced cancer who were receiving immune checkpoint inhibitors. These are immunotherapy drugs that release a “brake” on the immune system so it can attack the cancer. It was carried out in Israel by Bar-Sela and colleagues and published in Cancers in 2020. It followed 102 patients, 34 of whom used cannabis.
In that study, patients who used cannabis had a shorter time to progression (the time before the cancer started growing again). They also had shorter survival. The link was an association only. Confounding cannot be ruled out: another factor may explain the link. For example, if sicker patients were more likely to use cannabis, they would do worse whether or not cannabis played any part. The study does not prove that cannabis interfered with the drug.
The detailed figures and their limits are covered in Cannabis and Cancer: What the Evidence Supports and What It Does Not. One widely promoted preparation is covered in Rick Simpson Oil: What It Is, Where the Claims Came From, and What the Evidence Shows.
What to do if you are the patient: ask your oncologist two questions and write down the answers. What is the expected outcome for my cancer, at my stage, with treatment? What is it without treatment? Then ask how certain each estimate is for you personally. With these answers you can compare the two choices on real numbers.
Translator’s note: in Thailand, cannabis flower is a controlled herb. It can only be sold with a PT 33 prescription, for a maximum of 30 days per prescription. If you use any cannabis product, including oils, tell your oncology team. This matters most if you are on immunotherapy. They can then check for interactions and take it into account when reading your test results.
4. What Informed Refusal Looks Like in Practice
When a patient wants to decline treatment, the right response is neither pressure nor walking away. It is a clear process with six steps. Each step has a purpose.
- Check capacity properly when there is a real reason to doubt it. An unwelcome decision is not a reason. Purpose: to confirm that the right to refuse applies to this decision.
- Explain specifically. Do not just say “you should have the chemotherapy.” Give the expected outcome with treatment, the expected outcome without it, and how uncertain both estimates are for this person. Purpose: the patient decides on real information, not on general advice.
- Find out what is driving the refusal. It may be fear of a specific side effect, or a relative’s bad experience. It may be cost, distrust of doctors, or belief in an alternative. Purpose: each of these is a different problem with a different answer. Several can be solved without anyone changing their view about cannabis.
- Treat the two decisions separately. Declining chemotherapy and taking a cannabis preparation are separate choices. A patient can decline one treatment and still accept surgery or radiotherapy (radiation treatment). They can also still accept symptom control (treating pain, nausea and other symptoms) and palliative care (care focused on comfort and quality of life). Purpose: the patient does not lose all care by refusing one treatment. Refusal is not all-or-nothing and should never be presented that way.
- Write down what was discussed. Purpose: there is a record of what was explained and what was decided. The record also helps if the patient comes back later.
- Make it easy to come back. People change their minds. Purpose: a patient who changes their mind should not have to get past embarrassment before returning for treatment.
Translator’s note: relatives often join or lead these conversations. If the patient has capacity, the decision is still theirs. Ask the doctor to speak to the patient directly as well as to the family. If cost is the reason for refusing, ask the hospital’s social work or patient-rights office what your health coverage pays for before you decide. If you doubt the first opinion, the Declaration of Patient’s Rights and Duties gives you the right to ask for a second one.
What to do if you are a patient or carer: take this list to your next appointment. Go through the steps one by one with the doctor. At the end you should know the numbers, your real reason for hesitating, and which care stays available whatever you decide.
Questions about this part? Post them below this topic. Please do not post anything that could identify another person. The forum’s posting rules are in the Community Guidelines.
General information only. This is not medical advice and not legal advice. Legal provisions are summarised from published sources as of October 2026 and may change. Check current requirements with a qualified professional before relying on them.
References
- Johnson SB, Park HS, Gross CP, Yu JB. Use of alternative medicine for cancer and its impact on survival. Journal of the National Cancer Institute, 2018;110(1):121–124. doi:10.1093/jnci/djx145
- Johnson SB, Park HS, Gross CP, Yu JB. Complementary medicine, refusal of conventional cancer therapy, and survival among patients with curable cancers. JAMA Oncology, 2018;4(10):1375–1381. doi:10.1001/jamaoncol.2018.2487
- Bar-Sela G, Cohen I, Campisi-Pinto S, et al. Cannabis consumption used by cancer patients during immunotherapy correlates with poor clinical outcome. Cancers (Basel), 2020;12(9):2447. doi:10.3390/cancers12092447
- Mental Capacity Act 2005 (United Kingdom).
- National Health Act B.E. 2550 (2007), Section 12 (Thailand), and the Ministerial Regulation of B.E. 2553 on the procedure.
- Declaration of Patient’s Rights and Duties, Medical Council of Thailand and other health professional councils, 2015.
Continued in Part 2: When a Patient Declines Cancer Treatment in Favour of Cannabis: Children, Online Advice and Who Carries the Legal Risk (Part 2 of 2)