If you want to know how good the evidence for medical cannabis gets, look at multiple sclerosis. There is a licensed medicine, several randomised controlled trials, and a positive verdict from the 2017 US National Academies review. There is also a finding those same trials produced that almost nobody quotes: patients reliably say it helps, and clinicians measuring the same patients frequently cannot see it.
What this is about. Nothing here concerns treating multiple sclerosis itself. Cannabis does not modify the disease, does not slow progression, does not affect relapse rate and does not repair myelin. Everything below is about symptoms — spasticity, bladder urgency, pain — in people already under neurological care. This is general information, not medical advice. In Thailand cannabis flower is a controlled herb dispensed only on prescription form PT 33, and no one should change a disease-modifying therapy or an antispasticity drug on the basis of a forum article.
1. Why MS Is the Test Case
Multiple sclerosis is an autoimmune disease of the brain and spinal cord in which the immune system attacks the myelin sheath around nerve fibres. Its symptom burden is wide, and three parts of it — spasticity (involuntary muscle stiffness and spasm), bladder urgency and urge incontinence, and neuropathic pain — respond poorly to existing drugs in a substantial minority of patients.
That combination is what made MS the proving ground for cannabinoid medicine: a defined symptom, an inadequate standard of care, a measurable endpoint, and a patient population willing to be studied. The result is that MS symptoms are one of the most heavily trialled indications for cannabinoids.
2. The Spasticity Trial
Corey-Bloom and colleagues, Canadian Medical Association Journal, 2012 — a randomised, double-blind, placebo-controlled crossover trial with an eleven-day washout between phases.
Participants. 37 randomised, 30 completed; mean age about 50; 63% female; mean baseline modified Ashworth score 9.3. The modified Ashworth scale rates muscle tone from 0 to 4 in each muscle group, so 9.3 is a summed score across several muscle groups, not a single-joint rating. Critically, these were patients whose spasticity had not responded to conventional treatment.
Intervention. Cannabis cigarettes at approximately 4% THC, one per day for three consecutive days per phase, about four puffs each.
Results.
| Outcome | Cannabis versus placebo |
|---|---|
| Modified Ashworth spasticity score (summed across muscle groups) | −2.74 points (p < 0.0001) |
| Pain, visual analogue scale (0–100) | −5.28 points (p = 0.008) |
| PASAT cognitive test | −8.67 points (p = 0.003) — worse |
Read the scales before reading the numbers. The Ashworth change of 2.74 points comes off a summed baseline of 9.3, which is roughly a 30% reduction. The pain figure is on a 0–100 scale, so 5.28 points is a modest effect. It is not the dramatic change it would be on a 0–10 scale.
Five participants withdrew because of adverse effects: uncomfortable intoxication, dizziness, fatigue. No serious adverse events.
Two things deserve attention. The spasticity effect is substantial, and it was seen in patients whom other treatments had failed. And the third row is part of the result, not a footnote. The same trial that found the benefit measured an acute cognitive cost and reported it, and the authors’ own recommendation was that future work should test whether lower doses give the benefit with less cognitive impact.
A trial that reports both is a trial worth trusting. Sources that quote the first row and drop the third are not summarising it, they are editing it.
3. The Bladder Trial
Freeman and colleagues, International Urogynecology Journal, 2006 — the CAMS-LUTS study. This is a sub-study of the large UK CAMS trial (Zajicek et al., Lancet, 2003), and it is worth stating precisely because it is frequently mis-described.
Design. 630 patients randomised to oral cannabis extract, oral THC, or matched placebo. Primary outcome: urge incontinence episodes recorded in patient diaries.
Results. Reduction in episode rate: cannabis extract 38%, THC 33%, placebo 18%. All three fell significantly from baseline (p < 0.01). Both active arms beat placebo — extract p = 0.005, THC p = 0.039.
Note the placebo arm. Eighteen per cent of episodes disappeared on an inert capsule. The effect attributable to the drug is the difference between arms in mean reduction of episode rate (about 15–20 points), not the 38% headline. Ignoring the placebo arm is the single most common error made in reading trial results, and it inflates every cannabis claim it touches.
The authors’ own wording was appropriately restrained: the findings are suggestive of a clinical effect on incontinence episodes in MS.
4. The Split That Matters Most
Here is the finding that separates a careful reading of this literature from a promotional one.
The US National Academies of Sciences, Engineering and Medicine reviewed the whole evidence base in 2017 and reached two different conclusions about the same symptom:
- Substantial evidence that oral cannabinoids are effective for improving patient-reported MS spasticity symptoms.
- Limited evidence for an effect on clinician-measured spasticity.
The same pattern appeared in the parent CAMS trial itself (Zajicek et al., Lancet, 2003). Its objective outcome, the Ashworth score, was negative, while patient-reported spasticity improved.
There are several honest explanations and the data does not choose between them. The Ashworth scale may be too crude to detect what patients feel. What patients experience as “less stiffness” may be partly reduced pain and reduced distress rather than reduced muscle tone. Or blinding may fail — a drug with noticeable psychoactive effects tells the patient which arm they are in, and expectation does the rest.
None of those possibilities makes the patient wrong. If someone’s daily experience of stiffness improves, that is a real outcome and arguably the one that matters. But it does mean that “cannabis reduces spasticity in MS” is a claim about self-report that a measuring instrument has not consistently confirmed — and anyone quoting the evidence should say which of the two they mean.
5. The Licensed Medicine
Nabiximols (Sativex) is an oromucosal spray containing a roughly 1:1 ratio of THC and CBD, delivering about 2.7 mg THC and 2.5 mg CBD per spray. It was first approved in Canada (2005, conditional, for neuropathic pain in MS). It was approved in the UK in 2010 for MS spasticity, then in several EU countries. It is not approved in the United States. For the wider picture of approved cannabinoid medicines, see the article on that topic (bai99) rather than repeating it here.
Its evidence record is mixed in a way worth stating plainly rather than smoothing over:
- Collin et al., 2007 (European Journal of Neurology, 189 patients, six weeks): patient-rated spasticity fell by 1.18 points on the 0–10 numeric scale against 0.63 for placebo (p = 0.048). About 4 in 10 treated patients achieved at least a 30% improvement.
- Collin et al., 2010: a 15-week trial of 337 patients did not reach statistical significance on its primary analysis.
- Lakhan & Rowland, 2009 (BMC Neurology): a systematic review of six THC/CBD extract trials. It found a trend toward reduced spasticity but noted that outcome measures varied widely between studies.
- Novotna et al., 2011 (European Journal of Neurology): this trial used an “enriched” design. All 572 patients first took the spray single-blind for four weeks. Only those who improved by at least 20% went on to the randomised phase, and that was just under half of them (272). In that pre-selected group, nabiximols beat placebo clearly.
The American Academy of Neurology’s 2014 review classified nabiximols as probably effective for patient-reported spasticity symptoms and pain. The same review found the evidence for smoked cannabis in MS insufficient. That matters because the headline spasticity trial in section 2 used cigarettes. The licensed product is an oromucosal spray, and smoking is not a recommended medical route (see topic 1311).
These responder figures are the most useful numbers in this article. They show that the drug works well for some patients and not at all for others. That is exactly why the licensed indication in Europe is written as an add-on for patients who have not responded adequately to other antispasticity medication. It is also why prescribing practice uses a defined trial period with a stopping rule rather than open-ended use.
6. What This Does Not Say
It is not disease modification. Nothing above affects the underlying autoimmune process. Disease-modifying therapies do that, and they are not interchangeable with symptom relief.
It is not a reason to stop anything. Baclofen, tizanidine, disease-modifying therapy, bladder anticholinergics — none of these should be altered outside a neurologist’s direction.
It is not a general licence. The trials were in patients whose symptoms had already failed conventional treatment. That is the population studied, and it is where the licensed indication sits.
It is not an endorsement of smoking. The positive smoked-cannabis trial is small and short, and the AAN rated the smoked-cannabis evidence in MS as insufficient.
Spasticity from other causes, such as spinal cord injury, is covered separately (bai183). The MS results above should not be assumed to transfer to it.
7. In Thailand
Cannabis flower is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568, issued 26 June 2025. It can be dispensed only on prescription form PT 33 from an authorised practitioner, for no more than thirty days per prescription, with no refills, and from a GACP-certified source. Online sale and advertising of flower are not permitted. Two 2026 Ministerial Regulations tightened licensing but did not change these prescription rules.
Whether nabiximols itself is registered and available in Thailand is a separate question from whether flower is prescribable. Check it with a neurologist or hospital pharmacy rather than assuming it: an approval in Europe is not a Thai registration.
MS is relatively uncommon in Thailand and the rest of Southeast Asia. A significant share of demyelinating disease in the region is neuromyelitis optica spectrum disorder (NMOSD). NMOSD is a distinct condition with different treatment, and it must not be treated as MS. None of the trials above included NMOSD patients, so their results cannot be applied to it.
Related discussions: topic 1358 and topic 1311.
If you live with MS in Thailand or the region: did your neurologist raise cannabis, or did you? And if you have used it under prescription, was the change you noticed in the stiffness itself, in the pain, or in how much the symptom bothered you? The trials suggest those may be three different things, and patient descriptions are the only way to see which.
General information, not medical advice. Cannabis does not treat multiple sclerosis; decisions about symptom management belong with your neurologist.