The best trial of cannabis in ulcerative colitis found that patients felt much better. Bowel movements fell from about 2.6 a day to one, and quality of life rose clearly. However, the blood and stool tests for inflammation did not change significantly. Through a camera, the bowel lining did not look significantly different from the placebo groupâs. This article explains that gap in rheumatoid arthritis and inflammatory bowel disease. It also explains why the gap means you should never stop your regular medicine.
Read this first. Nothing in this article supports reducing or stopping any of these medicines:
- immunosuppressants (medicines that damp down the immune system)
- biologics (antibody medicines given by injection or drip)
- disease-modifying antirheumatic drugs (medicines that slow joint damage in rheumatoid arthritis)
- mesalazine (a standard anti-inflammatory medicine for ulcerative colitis)
In autoimmune disease, feeling better and being better are different things. You may not feel inflammation, but it still causes damage: eroded joints, narrowed bowel and surgery. Symptom relief is not remission, which means the disease itself is under control. This is general information, not medical advice. In Thailand, cannabis flower is a controlled herb and is dispensed only on a PT 33 prescription.
1. Why researchers expected cannabis to calm the immune system
The body has its own cannabinoid signalling network, called the endocannabinoid system. One of its receptors, CB2, sits mainly on immune cells. Researchers have proposed acting on CB2 to reduce inflammation in many conditions.
In the gut, this system does several jobs. It affects how fast the bowel moves, how much fluid it secretes and how sensitive it feels. It also takes part in immune signalling there.
Autoimmune diseases happen when the immune system attacks the bodyâs own tissue. Cannabinoids act on immune signalling. So it was reasonable to expect that they might slow the disease itself, not just hide the symptoms. That idea has now been tested in human trials, which are described below.
What to do: when someone uses receptor science as proof that cannabis treats a disease, ask which human trial measured the inflammation.
2. Two tests that measure real inflammation in the bowel
Symptoms are what you feel, such as pain, diarrhoea or tiredness. Inflammation is what is actually happening in the tissue. The two can disagree. That is why bowel specialists (gastroenterologists) check inflammation with laboratory tests and do not rely on symptoms alone.
- CRP (C-reactive protein) is measured in a blood sample. The liver makes it in response to inflammation. A high level shows there is inflammation somewhere in the body, but not where it is or what causes it.
- Faecal calprotectin is measured in a stool sample. It is a protein released by white blood cells that move into inflamed bowel tissue. A high level therefore points to inflammation in the bowel itself, but it does not show the cause.
A third check is endoscopy. A doctor passes a small camera into the bowel and grades how inflamed the lining looks. In ulcerative colitis, a common grading scale is the Mayo endoscopic score. A lower number means a healthier lining.
What to do: if you have inflammatory bowel disease, ask your specialist for your latest CRP, calprotectin and endoscopy results, and write them down. You need these starting numbers to judge any later change.
3. Ulcerative colitis: the trial that separates symptoms from inflammation
Inflammatory bowel disease (IBD) covers two main conditions, ulcerative colitis and Crohnâs disease. Ulcerative colitis inflames the lining of the large bowel. In 2021, a research team led by Naftali in Israel published the strongest controlled trial so far in the journal PLOS ONE.
The trial had 32 patients with mild to moderate ulcerative colitis, average age 30. Each was randomly assigned to THC-rich cannabis cigarettes or placebo cigarettes for eight weeks. Each cigarette held 0.5 g of cannabis containing 80 mg THC.
The table uses two terms. The Lichtiger index is a disease activity score for ulcerative colitis, based mainly on symptoms. Lower is better. The p value shows how likely a result is to be chance. Below 0.05 is the usual cut-off for treating a result as real.
What improved:
| Outcome | Cannabis group | Placebo group |
|---|---|---|
| Lichtiger disease activity index | 10.9 â 5 (p < 0.001) | 11 â 8 (p = 0.37) |
| Quality of life score | 77 â 98 (p = 0.001) | No significant change |
| Daily bowel movements | 2.6 â 1 (p < 0.001) | 2.6 â 2 (p = 0.168) |
What did not improve:
- The Mayo endoscopic score fell within the cannabis group, from 2.13 to 1.25 (p = 0.015). The difference between the cannabis and placebo groups was not significant (p = 0.374). So the trial could not show that the bowel lining healed better on cannabis than on placebo.
- Blood count, CRP and faecal calprotectin did not change significantly in either group.
Side effects were minor: 35% reported dizziness and 29% confusion. Nobody dropped out because of them.
The researchersâ own conclusion is the key point. Cannabis brought clinical remission and better quality of life. However, these effects were not linked to a significant improvement in the objective measures of inflammation.
The cannabis in this trial was smoked. Do not copy that route. Smoking harms the lungs. That harm adds up when cannabis is used long term alongside treatment, and smoking is not a recommended route (see Routes of Administration).
What to do: if you discuss cannabis with your doctor, ask about non-smoked routes, and read the routes article above before the appointment.
4. Crohnâs disease: the same pattern
Crohnâs disease is the second main form of IBD. The same Naftali group published a Crohnâs trial in the Journal of Crohnâs and Colitis in 2021. It had 56 patients, each randomly assigned for eight weeks to an oral cannabis oil or placebo. The oil was rich in CBD, with 160 mg/ml CBD and 40 mg/ml THC.
Disease activity improved significantly in the cannabis group, measured by the CDAI (Crohnâs Disease Activity Index), a score built mainly from symptoms. Quality of life improved as well. The endoscopic score, CRP and calprotectin did not change significantly. The researchers concluded that cannabis in Crohnâs disease should be used only within clinical trials.
The same group ran an earlier pilot trial with 21 patients, published in Clinical Gastroenterology and Hepatology in 2013. Those patients smoked cannabis. It showed a better clinical response than placebo but no significant difference in remission. A trial this small cannot carry much weight.
What to do: if you have Crohnâs disease, keep your planned endoscopies and blood and stool tests on schedule, whatever you try for symptoms.
5. Why feeling better is not the same as being better
In ulcerative colitis and Crohnâs disease, symptoms and inflammation can drift apart in either direction. A patient can feel well while the bowel is still inflamed. Unfelt inflammation still leads to the outcomes that matter. These include strictures (narrowed sections of bowel), fistulas (abnormal tunnels from the bowel to nearby organs or skin) and surgery. In colitis, there is also a higher long-term risk of cancer.
For this reason, modern IBD care aims for mucosal healing: a healed bowel lining confirmed by endoscopy. Symptom control alone is not the target.
A grower will recognise the problem from root rot. A foliar feed can make the leaves look greener for a while. The roots keep rotting until someone actually checks them.
So a treatment that eases symptoms without reducing inflammation cannot replace one that does. At most, it can be added on top. Even then it carries a specific danger. It can mask the warning signs that would otherwise make your doctor step up the real treatment.
What to do: keep every scheduled test and endoscopy even when you feel well, because feeling well is exactly when masking happens.
6. What surveys and smaller studies report, and a warning sign
Most reports of patient benefit come from surveys and small retrospective studies, which look back at past records:
- Lal and colleagues (European Journal of Gastroenterology & Hepatology, 2011) surveyed IBD patients at a hospital clinic in Toronto (Canada). Cannabis use was common, mostly for abdominal pain, diarrhoea and poor appetite.
- The Naftali group (Israel Medical Association Journal, 2011) reviewed 30 Crohnâs patients. They reported lower disease activity scores and a reduced need for other medication.
- The 2013 pilot trial above reported that three patients no longer needed long-term steroids.
Treat the medication finding with real caution. These reductions were uncontrolled, meaning there was no comparison group. They were also unblinded: patients and doctors knew who was using cannabis. And they come from a disease where controlled trials found no improvement in objective markers. That combination is exactly when someone can feel fine while the disease progresses.
A separate team also found a warning sign. Storr and colleagues, a research group in Calgary (Canada), surveyed 313 IBD patients (Inflammatory Bowel Diseases, 2014). Cannabis relieved pain and diarrhoea. However, some Crohnâs patients had used it for IBD symptoms for more than six months. That group had higher odds of surgery, with an odds ratio of about 5. Put simply, their odds of having had surgery were about five times higher.
This is an association, not proof of cause. Patients with more severe disease may simply use more cannabis. However, the pattern is what you would expect if symptom relief were hiding disease that kept getting worse. It is the strongest reason to keep watching the markers.
What to do: if you have used cannabis for Crohnâs symptoms for more than six months, tell your specialist. Ask whether your inflammation markers or endoscopy are due.
7. Rheumatoid arthritis: one small trial from 2006
In rheumatoid arthritis, the immune system attacks the lining of the joints. The key study is by Blake and colleagues, a team in the United Kingdom, published in Rheumatology in 2006. As of 2026, it was the only published randomised controlled trial that could be found of a cannabis-based medicine specifically in rheumatoid arthritis. Nearly every claim made in this area comes from it.
Design. The trial had 58 patients, 31 on the active medicine and 27 on placebo, for five weeks. The medicine was nabiximols, a spray used inside the mouth in the evening. In the final week, patients used an average of 5.4 sprays a day.
Results. These measures improved significantly:
- pain on movement
- pain at rest
- sleep quality
- the DAS28 disease activity score
- the pain part of the Short-Form McGill Pain Questionnaire, a standard pain questionnaire
Morning stiffness did not improve significantly, but it was already low at the start.
Safety. Most side effects were mild or moderate. In the active group, no one withdrew because of side effects and there were no serious side effects.
The researchers judged the benefits clinically relevant and called for more detailed research. Two limits matter here. First, 58 patients over five weeks is a preliminary trial, and the researchers used that word in their own title. Second, in the twenty years since, that larger research has mostly not happened. Small promising trials without follow-up are common in this field. Usually that is not because a follow-up was unnecessary.
DAS28 combines counts of tender and swollen joints, out of 28 joints, with a blood test for inflammation (ESR or CRP) and the patientâs own rating of overall health. So it is not purely subjective. However, it does not use imaging such as X-rays to measure joint damage.
The trial product was nabiximols (Sativex). Readers in Thailand should not assume they can get it. Results from a standardised pharmaceutical spray also cannot be applied to other cannabis products.
Translatorâs note: homegrown flower is not a standardised product either. THC and CBD content changes from plant to plant and from batch to batch. The trial doses therefore tell you nothing about what a flower or oil from a garden delivers.
What to do: if you have rheumatoid arthritis, ask your rheumatologist to record your DAS28 score before you add anything. Ask for any planned joint imaging too, so later changes can be compared.
8. Osteoarthritis is a different disease
Most people searching for âcannabis for arthritisâ mean osteoarthritis or general joint pain. That is joint wear and breakdown, not an immune attack on the joints. The rheumatoid arthritis results above do not apply to it.
The best placebo-controlled CBD trial that could be found was by Vela and colleagues (Pain, 2022). People with hand osteoarthritis or psoriatic arthritis took 20â30 mg of synthetic CBD daily for 12 weeks. Pain did not improve significantly compared with placebo.
What to do: check which type of arthritis you were diagnosed with before you read any study, because the evidence for each type is different.
9. Laboratory evidence, and the drug that failed in people
Two lines of laboratory work are often quoted:
- Malfait and colleagues (PNAS, 2000) studied mice with collagen-induced arthritis, a laboratory model of rheumatoid arthritis. The mice received CBD after symptoms had started, by injection or by mouth. CBD stopped the arthritis getting worse and reduced joint damage. The effect followed a bell-shaped dose curve: middle doses worked better than low or high ones.
- When the body breaks down THC, the main product is THC-11-oic acid. It showed anti-inflammatory activity without a psychoactive effect. A synthetic derivative called ajulemic acid reduced joint injury in rats with adjuvant arthritis, another laboratory arthritis model (Zurier and colleagues, Arthritis & Rheumatism, 1998).
Animal results are weaker evidence than results in patients, and the next step shows why. Ajulemic acid was developed as a drug under the name lenabasum. It then failed its main goals in phase 3 trials, the large final trials before approval. These were in systemic sclerosis (2020) and dermatomyositis (2021), two other autoimmune diseases.
Some people also suggest applying cannabis to the skin over the joints. The article on cannabis on the skin explains what topical cannabinoids can and cannot be expected to do.
What to do: when a website quotes a mouse or rat study as proof, look for the human phase 3 result before you believe the claim.
10. What the evidence adds up to
Inflammatory bowel disease: two small controlled trials found that symptoms and quality of life improved over eight weeks, one in ulcerative colitis and one in Crohnâs disease. There is no evidence of an anti-inflammatory effect on objective markers. Observational data link longer use in Crohnâs disease with more surgery. That fits the documented risk of masking active disease.
Rheumatoid arthritis: one small, positive, five-week trial from 2006, with almost no follow-up. Osteoarthritis: the placebo-controlled CBD evidence that could be found is negative.
For all of them: cannabis can at most be an add-on. Discuss it with the specialist who manages the disease. Judge it on symptoms, and use it alongside the treatment that controls the disease, never instead of it.
A gastroenterologist or rheumatologist would recognise the sensible position. If a patient wants to try cannabis for symptoms, the answer is not a flat refusal. The answer is: âYes, alongside your treatment, and we keep monitoring the markers.â From then on, the markers are the only thing that tells patient and doctor whether the disease is still under treatment.
What to do: if you decide to try cannabis for symptoms, agree on a monitoring plan with your specialist before you start. The plan should say which tests you will have and when.
11. The situation in Thailand (October 2026)
Translatorâs note: cannabis flower is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568. It was issued under the Thai Traditional Medicine Protection Act B.E. 2542 and came into force on 26 June 2025. Flower may be sold only on a PT 33 prescription, covering no more than 30 days. Advertising and online sale of flower are prohibited.
Translatorâs note: two Ministerial Regulations of B.E. 2569 followed in 2026 (summary). The regulation on cannabis or hemp extracts came into force on 26 April 2026. The Ministerial Regulation on Controlled Herbs (No. 2) came into force on 30 April 2026 and tightened the licence criteria for cannabis flower. The draft Cannabis Control Act is not law yet. The Cabinet approved the draft on 22 September 2026 and sent it to the House. For the background up to 2024, see Thailandâs Cannabis Rules, 2022 to 2026.
Translatorâs note: biologics and immunosuppressants carry their own risk of infection. That is one more reason your specialist must know about anything you add. If you get a PT 33 prescription, tell the prescriber which immunosuppressant or biologic you take. Then tell your specialist about the prescription. A written list helps, see Cannabis Drug Interactions. Also ask the hospital that manages your IBD how often it repeats CRP tests, and whether it offers calprotectin testing.
What to do: get any cannabis flower only through a PT 33 prescription, and make sure both doctors know what the other has prescribed.
12. Step by step, if you have one of these conditions
- Do not change your regular medicine yourself. These medicines control the inflammation. Cannabis has not been shown to do that.
- Record your starting numbers before you add anything. For IBD that means CRP, faecal calprotectin and the latest endoscopy result. For rheumatoid arthritis it means DAS28 and any joint imaging. Without starting numbers, nobody can tell whether the disease changed.
- Keep a symptom diary for at least eight weeks, the length of the bowel trials. Note daily bowel movements or pain, sleep, and side effects such as dizziness or confusion. This shows how symptoms changed separately from the tests.
- Ask for the markers to be repeated at your next visit, then compare them with your starting numbers. This is the only way to know whether the disease is still controlled.
- Avoid smoking as a route. Long-term use alongside treatment adds up the lung harm.
- If you feel better but your markers are worse, tell your specialist straight away. This is the masking pattern described in section 5.
Discussion: if you have IBD or rheumatoid arthritis and have used a cannabinoid alongside your treatment, please share below. Which tests did your specialist keep checking, how often, and what did they show? Questions about this article are welcome in this topic too.
This article is part of the Asiannabis Community educational series on medical cannabis. It is general information, not medical advice. Never reduce or stop an immunosuppressant, biologic or disease-modifying drug except under the direction of your specialist.
References
- Naftali and colleagues. Randomised placebo-controlled trial of THC-rich cannabis cigarettes in ulcerative colitis. PLOS ONE, 2021.
- Naftali and colleagues. Randomised placebo-controlled trial of CBD-rich cannabis oil in Crohnâs disease. Journal of Crohnâs and Colitis, 2021.
- Naftali and colleagues. Pilot trial of smoked cannabis in Crohnâs disease. Clinical Gastroenterology and Hepatology, 2013.
- Naftali and colleagues. Retrospective study of cannabis in 30 Crohnâs disease patients. Israel Medical Association Journal, 2011.
- Lal and colleagues. Survey of cannabis use among IBD patients in Toronto. European Journal of Gastroenterology & Hepatology, 2011.
- Storr and colleagues. Survey of 313 IBD patients in Calgary. Inflammatory Bowel Diseases, 2014.
- Blake and colleagues. Preliminary trial of nabiximols in rheumatoid arthritis. Rheumatology, 2006.
- Vela and colleagues. Synthetic CBD in hand osteoarthritis and psoriatic arthritis. Pain, 2022.
- Malfait and colleagues. CBD in collagen-induced arthritis in mice. PNAS, 2000.
- Zurier and colleagues. Ajulemic acid in adjuvant arthritis in rats. Arthritis & Rheumatism, 1998.
- Phase 3 trials of lenabasum (ajulemic acid) in systemic sclerosis (2020) and dermatomyositis (2021), as cited in the original article.