Pain is the most common reason people look for medical cannabis, yet the evidence is weaker than most people assume. The best-known trial was run at McGill University in Canada. Its strongest cannabis lowered pain by an average of 0.7 points more than placebo on a 0–10 scale [1]. That result is statistically significant, but it is small.
This part covers four topics. It looks at what the evidence shows when many trials are pooled, including a Cochrane review from January 2026. It explains why the placebo effect is so large in pain studies. It shows how one patient can try cannabis safely under supervision. Finally, it sets out the rules in Thailand.
Do not stop or reduce a prescribed pain medicine because of this article. Nothing here is a reason to change any medicine. Opioids are strong prescription painkillers, such as morphine. Stopping them or other prescribed pain medicines suddenly can be dangerous. In Thailand, cannabis flower is a controlled herb. It is dispensed only against a prescription on form PT 33 from an authorised practitioner. Any change to your treatment belongs with the person who prescribed it.
This is Part 2. Part 1: Cannabis and Chronic Pain: The Mechanism, the Trials, and Why the Evidence Is Weaker Than the Demand
4. What the Evidence Shows When Trials Are Pooled
Individual cannabis pain trials are small, often with only 20–30 people. To get a clearer answer, researchers run a systematic review. A systematic review collects every trial on one question using fixed rules and grades the quality of each. When the numbers are also combined, it is called a meta-analysis.
Cochrane is an international research network known for very strict reviews of this kind. In January 2026, a team led by Ateş and Häuser updated Cochrane’s existing review on cannabis-based medicines for chronic neuropathic (nerve) pain in adults [2]. It covers 21 trials and more than 2,100 adults. Treatment periods ranged from two to 26 weeks.
The review found:
- There is no high-quality evidence that cannabis-based medicines relieve nerve pain better than placebo. This held for all three product types: mostly-THC, mostly-CBD, and balanced THC/CBD.
- Balanced THC/CBD products gave small improvements. These fell short of clinical significance, meaning they were too small for patients to feel as a real difference.
- Most of the trials were too poor in quality to draw firm conclusions.
- Products containing THC caused more dizziness and drowsiness. They possibly also caused more people to drop out of trials because of side effects. Trials reported side effects inconsistently, so even this finding has low to very low certainty.
- The authors call for larger studies lasting at least 12 weeks. These should include people with comorbidities: other physical or mental illnesses at the same time, as real patients often have.
This is the current position of one of the strictest groups in the field, published in January 2026. It is more negative than most public discussion assumes.
Two Earlier Guidance Documents
The International Association for the Study of Pain (IASP) is a worldwide professional body of pain researchers and clinicians. In March 2021, it stated that it does not endorse the general use of cannabinoids for pain. Its reason was the lack of high-quality evidence [3].
Later in 2021, the British Medical Journal (BMJ) published a fast-track clinical guideline, called a BMJ Rapid Recommendation [4]. It made a weak recommendation. Doctors may offer adults with chronic pain a trial of non-inhaled medical cannabis or cannabinoids when standard care is not enough. “Non-inhaled” means taken without smoking or vaping it. The route of use changes how the body takes up cannabis.
The BMJ panel judged the benefits to be small and only just greater than the harms. So it recommended shared decision-making, where the doctor and patient weigh the pros and cons together before deciding. Neither document claims that cannabis is an effective first-line treatment, meaning the first treatment to try.
One Licensed Cannabis Medicine
Nabiximols (brand name Sativex) has its own approval history. It is a mouth spray containing THC and CBD. It is licensed in a number of countries, mainly for spasticity in multiple sclerosis (MS). Spasticity means muscle stiffness and spasms. In 2005, Canada also gave it conditional approval as an add-on treatment for nerve pain in MS. For details, see the article on cannabis and multiple sclerosis.
Translator’s note: We could not confirm that nabiximols (Sativex) is registered in Thailand, so do not assume it is available here. The Government Pharmaceutical Organization (GPO) makes cannabis oils taken under the tongue, in THC-dominant, CBD-dominant and 1:1 CBD:THC formulas. Patients get them on a doctor’s prescription at medical cannabis clinics. Cannabis or hemp extracts above 0.2% THC fall under a separate law, the Ministerial Regulation on Cannabis or Hemp Extracts B.E. 2569. It has been in force since 26 April 2026 (summary of the 2026 regulations). Only three kinds of body can hold a licence for these extracts. The first is Thai juristic persons that are not “foreign” under the Foreign Business Act B.E. 2542. The others are state agencies and the Thai Red Cross Society.
What to do: If your doctor suggests trying cannabis for pain, ask whether a non-inhaled form is available to you. Ask where the product comes from. The guideline that supports a trial covers only non-inhaled forms.
5. The Placebo Effect Is Unusually Large in Pain Trials
A placebo effect is an improvement that comes from receiving a treatment at all, even a dummy one. Pain trials measure pain by what patients report, not by a lab test. Placebo effects are strongest on self-reported outcomes like this.
Gedin and colleagues published a meta-analysis in JAMA Network Open, a journal of the American Medical Association, in 2022 [5]. They pooled 20 double-blind, placebo-controlled trials of cannabis-based treatments in adults with clinical pain, with 1,459 participants in total.
The study reported results as “Hedges g”. This is an effect size: one number that lets you compare studies that used different pain scales. By common convention, about 0.2 is a small effect, 0.5 moderate and 0.8 large.
The results:
- Placebo alone reduced pain significantly, by a moderate-to-large amount (g = 0.64).
- Trials at low risk of bias (well-designed trials with few flaws) showed larger placebo responses.
- The active cannabinoid produced a large effect (g = 0.95).
- The difference between the cannabinoid and placebo was not statistically significant (g = 0.32, P = .09). P is the chance of seeing such a result if there were no real difference. A P value below 0.05 is usually needed to call a result significant, and 0.09 is above that.
The same study also looked at media coverage. These trials received heavy news coverage, with a strong positive slant. The study also measured attention scores, which track how widely a paper is shared and discussed. Neither the number of positive news stories nor the attention scores matched how large the effects really were.
None of this means the relief patients feel is imaginary. Placebo pain relief is a real physical process in the body, and the relief is real to the person who feels it. The point is narrower than that. It is very hard to measure how much of the relief comes from the cannabinoid itself, and the trials so far have largely failed to measure it.
What to do: When you read a news story about cannabis and pain, look for the comparison with placebo. Ignore the simple “before and after” change. A before-and-after change includes the placebo effect, so it always looks bigger than the drug’s own effect.
6. What a Small Average Means for One Person
A small average difference in a trial can hide two very different situations. Everyone might get a small benefit. Or a minority might get a large benefit while most people get none. People who get a clear benefit are called responders. When their results are averaged with those of non-responders, the average looks modest.
Trials that report averages cannot easily tell these two situations apart. Research has also not yet found a reliable way to predict who will respond. This is the honest reason a supervised trial for one person can be reasonable, even when the average effect is weak. Your question is not “what is the average across 2,100 people?” Your question is “am I one of the people it helps?”
The only way to answer that is a structured trial, set up with your prescriber, that meets two conditions:
- It is supervised. A doctor judges the result, so you are not deciding based on hope.
- It has a stopping rule agreed in advance. This stops “it isn’t working yet” from turning into ever-higher doses with no end point.
What to do:
- Keep a pain diary for two weeks before you start. Record three separate scores each day: pain intensity, sleep quality, and how much the pain bothered you. This gives you a baseline to compare against.
- Before starting, agree with your prescriber which of those scores you will judge by, and how much change counts as success.
- Set a review date. Agree in advance that if the change has not been reached by then, you stop.
Some patient surveys add a finding worth setting beside the trial data. Some respondents said their usual painkillers relieved pain more effectively than cannabis. They chose cannabis anyway because they preferred its side effects. That is a sensible, reasonable choice. It is still a different claim from “cannabis works better”. An honest account of this field needs to keep both points in view.
7. Two Things This Article Is Not Saying
It is not saying that cannabis does nothing for pain. The mechanism is real, and some trials are positive. Better sleep is reported consistently. The patient preference described above is legitimate.
It is not a reason to stop anything. Whether cannabis lets patients lower their opioid doses is a separate and disputed question. It is covered in Cannabis as Substitution for Alcohol and Opioids. Whatever the answer turns out to be, suddenly stopping a prescribed opioid or other painkiller is dangerous. That decision belongs to a prescriber, not to a forum.
What to do: If you want to reduce a painkiller, raise it at your next appointment. Bring a full list of everything you take, including cannabis (what to put on the list). This lets your doctor check for interactions between medicines and plan any reduction safely.
8. The Rules and Medical Guidance in Thailand
Cannabis flower is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568. This notification was issued under the Thai Traditional Medicine Protection Act B.E. 2542 and has been in force since 26 June 2025 [6]. The main rules are:
- Flower can only be supplied against a PT 33 prescription from an authorised practitioner, for their own patient.
- Each prescription may cover no more than 30 days.
- The flower must come from sources certified under the good agricultural and collection practice (GACP) standard of the Department of Thai Traditional and Alternative Medicine. GACP sets out how a medicinal plant must be grown, harvested, dried and recorded.
- Advertising cannabis flower and selling it online are prohibited.
A separate Cannabis Control Act is still only a draft and is not law yet. The Cabinet approved the draft on 22 September 2026 and sent it to the House of Representatives (where the draft stands).
The Department of Medical Services (DMS) of the Thai Ministry of Public Health has issued guidance on medical cannabis. It lists neuropathic pain among the conditions where research shows evidence of benefit. The same guidance says cannabis products should not be the first-line treatment: standard treatment comes first. This guidance was written before the 2026 Cochrane update, which reads the trial evidence more cautiously.
Translator’s note: The practical place to start is the doctor who already treats your pain. Ask whether a supervised cannabis trial is reasonable for your type of pain. Many Thai public hospitals have a medical cannabis clinic, so also ask whether you can be referred to one. Bring your two-week pain diary. A PT 33 prescription covers 30 days at most. So it makes sense to set your first review date at or before the end of the first prescription.
Translator’s note: Do not give or sell flower to a friend or relative who has pain, even if you grow it yourself. Selling a controlled herb without a licence breaks Section 46 of the Thai Traditional Medicine Protection Act B.E. 2542. Under Section 78, the penalty is up to 1 year in prison and/or a fine of up to 20,000 baht. Offering flower for pain patients on this forum also counts as advertising or online sale, which are prohibited (what you may post).
Share your experience below this topic. If you use cannabis for chronic pain on prescription, tell us what kind of pain you have. Also tell us what changed: the pain intensity itself, your sleep, or how much the pain bothered you. These are three different outcomes, and the trials suggest they may not change together. Please describe outcomes, not doses. Do not advise anyone to change their medicine.
References
- Ware MA, et al. Smoked cannabis for chronic neuropathic pain: a randomized controlled trial. CMAJ. 2010;182(14):E694–E701. doi:10.1503/cmaj.091414
- Ateş G, Welsch P, Klose P, Phillips T, Lambers B, Häuser W, Radbruch L. Cannabis-based medicines for chronic neuropathic pain in adults. Cochrane Database of Systematic Reviews. 2026, Issue 1. doi:10.1002/14651858.CD012182.pub3
- International Association for the Study of Pain. IASP Position Statement on the Use of Cannabinoids to Treat Pain. 18 March 2021. https://www.iasp-pain.org/advocacy/iasp-statements/iasp-position-statement-on-the-use-of-cannabinoids-to-treat-pain/
- Busse JW, et al. Medical cannabis or cannabinoids for chronic pain: a clinical practice guideline. BMJ. 2021;374:n2040. doi:10.1136/bmj.n2040
- Gedin F, Blomé S, Pontén M, et al. Placebo response and media attention in randomized clinical trials assessing cannabis-based therapies for pain: a systematic review and meta-analysis. JAMA Network Open. 2022. doi:10.1001/jamanetworkopen.2022.43848
- Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568 (Royal Gazette, 25 June 2025). Summary: ประกาศกระทรวงสาธารณสุข เรื่อง สมุนไพรควบคุม (กัญชา) พ.ศ. 2568 - กองกัญชาทางการแพทย์
This article is part of the Asiannabis Community educational series on medical cannabis. It is general information, not medical advice. Do not change any prescribed treatment based on anything written here.