Fibromyalgia is a chronic pain condition that affects an estimated 1 in 20 adults in the UK, most of them women. Standard medicines such as amitriptyline, duloxetine and pregabalin help some patients but not others, and many people continue to live with poor sleep, fatigue and persistent pain. Interest in medical cannabis as an additional option has grown, but high-quality randomised evidence in fibromyalgia is still limited.
A new pilot trial published in Pain Research & Management is among the first randomised, double-blind, placebo-controlled studies of a 1:1 THC:CBD oil specifically designed to test whether a larger trial in fibromyalgia is feasible. The trial was small (24 participants), based in Australia, and intended to inform future research, not to change clinical practice. Below we summarise what the researchers did, what they found, and what it does and does not mean for UK patients.
What is Fibromyalgia?
Fibromyalgia is a long-term condition characterised by widespread musculoskeletal pain, fatigue, poor sleep and cognitive symptoms often described as “fibro fog”. Anxiety, low mood and irritable bowel syndrome commonly occur alongside it. The cause is not fully understood. Current evidence points to altered pain processing in the central nervous system, with a contribution from peripheral nerves. Symptoms may begin or worsen after a physical trauma, infection or major emotional event.
First-line treatment usually combines medication with physical and psychological therapies, including graded exercise and cognitive behavioural therapy (CBT). Commonly prescribed medicines include amitriptyline, duloxetine, milnacipran and pregabalin. These help some patients, but side effects are common and a substantial proportion of people do not achieve satisfactory symptom control. This is why patients and clinicians continue to look at additional options.
Why is medical cannabis being investigated in fibromyalgia?
The two most-studied compounds in the cannabis plant are delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD). They interact with the body’s endocannabinoid system, which has a role in pain, sleep and mood — three of the symptom domains that matter most in fibromyalgia. Preclinical and observational data have suggested possible benefits, but the field has had relatively few randomised, placebo-controlled trials, and most have been small. Pilot trials such as this one are designed to answer practical questions before larger efficacy trials are launched.
These include:
- Can patients be recruited?
- Do they tolerate the medicine?
- Is the design workable?
How was the study designed?
The trial was a double-blind, randomised, placebo-controlled pilot conducted in Australia and led by Kurlyandchik and colleagues. Twenty-four adults with fibromyalgia were randomised 1:1 to receive either a 1:1 THC:CBD oil (10 mg/mL of each cannabinoid) or a matched placebo oil. After a 4-week dose titration, participants entered 12 weeks of stable dosing. The full intervention was a single evening dose, chosen to support adherence, target sleep and minimise daytime psychoactive effects.
What were the outcomes of the study?
Outcomes were grouped into two tiers.
The primary outcomes of this study were the feasibility of both the trial procedures and the intervention. This was evaluated by examining recruitment and retention metrics, and compliance with the treatment schedule.
The study also assessed patient satisfaction using elected 5-point Likert scale questions specifically measuring satisfaction with the product, procedures and overall trial experience
Secondary outcomes covered the effect of treatment of common fibromyalgia symptoms, including:
- Fibromyalgia impact: Assessed using the Fibromyalgia Impact Questionnaire Revised (FIQR), a 21-item self-report measure comprising function, overall impact, and symptoms.
- Quality of life: Measured by the 36-item Short-Form Health Survey (SF-36), which assesses both physical and mental health.
- Pain: Evaluated using the ADPS (7-day mean) on an 11-point numeric scale based on the worst pain experienced in the past 24 hours.
- Depression and anxiety: Assessed with the Hospital Anxiety and Depression Scale (HADS), a 14-item self-report instrument featuring different subscales for anxiety and depression.
- Sleep quality: Measured using the Pittsburgh Sleep Quality Index (PSQI), a 19-item questionnaire with seven components.
- Fatigue: Assessed with the Multidimensional Fatigue Inventory (MFI-20), a 20-item scale covering general, physical, and mental fatigue, as well as motivation and activity levels.
What did the trial find?
Primary Outcomes
Recruitment and Retention: From 77 people pre-screened, 24 were randomised — a screening-to-randomisation ratio of around 3:1. Recruitment reached 66.7% of the target, with shortfalls mainly explained by geographic distance to the study site and patient concerns about legal issues such as driving while on medical cannabis in Australia.
Retention was strong: 22 of 24 participants (91.7%) completed the trial. All participants took at least 90% of prescribed doses, with an overall missed-dose rate of 1.2%.
Adverse Events: A total of 121 adverse events were reported across the trial. Most were mild, with no serious or life-threatening events. The most common side effects in the cannabis group were drowsiness, dizziness, fatigue, nausea and dry mouth — each reported by 4 to 5 participants. Two participants reduced their dose after titration because of morning drowsiness, daytime sleepiness, fatigue or memory effects. These findings are consistent with the known side-effect profile of THC-containing medicines.
Blinding: Around three-quarters of participants in each group correctly guessed which arm they were in, which is relevant to interpreting any open-label or expectancy effects.
Secondary Outcomes
These findings come from a sample of just 24 people and should be treated as preliminary. They are intended to inform the design of a larger trial, not to demonstrate efficacy.
Pain: Around 70% of participants on cannabis achieved a clinically meaningful reduction in pain (at least 30%) by Week 12, compared with 40% on placebo. Larger reductions (at least 50%) were also more common in the cannabis group.
Sleep Quality: Mean PSQI scores in the cannabis group went from 13.4 at enrolment to 8.5 at Week 12. Change in the placebo group was minimal.
Fibromyalgia Impact: A clinically meaningful improvement in total FIQR (at least 45.5% reduction) was seen in 40% of the cannabis group versus 10% of the placebo group, with medium to large between-group effects on function, impact and total score.
Quality of Life (SF-36): By Week 12, the cannabis group showed greater improvement than placebo on several SF-36 domains, particularly bodily pain, social functioning and mental health.
Fatigue (MFI-20) and Anxiety/Depression: The authors report no statistically significant between-group differences on the MFI-20 or HADS scales.
What does this mean for patients and clinicians in the UK?
Three points are worth taking from this trial.
First, a randomised, double-blind trial of a 1:1 THC:CBD oil in fibromyalgia is feasible. Adherence was excellent and the medicine was well tolerated in this small sample. The main barriers were practical (distance to the study site and concerns about driving) both of which are addressable in the design of a future trial.
Second, the efficacy signals are encouraging but preliminary. With only 24 participants, confidence intervals around effect sizes are wide, and three-quarters of participants correctly guessed their allocation, which may have inflated reported benefits through expectancy effects. The fatigue, anxiety and depression results, where no significant differences were seen, are a useful reminder not to over-interpret early data. Larger, adequately powered trials are needed before any firm conclusion can be drawn about whether medical cannabis improves fibromyalgia symptoms.
Third, the UK context differs from the Australian study setting. UK patients can only access medical cannabis through a specialist clinic, with formulation and dosing chosen and monitored by the prescriber. Fibromyalgia is not on the short list of indications for which UK guidance currently recommends cannabis-based medicines, and any prescription is an unlicensed, off-label use made on an individual basis. Patients considering this route should weigh potential benefits against side effects (especially drowsiness and dizziness), interactions with existing medicines, and the requirement to avoid driving while impaired.
Speak to a Specialist
If you are living with fibromyalgia and are struggling to achieve adequate relief from conventional treatments, it is important to speak to a healthcare professional about your options. Medical cannabis treatment should always be considered on a patient-by-patient basis, taking your medical history and any past treatments into account.
If you’d like to find out if a medical cannabis consultation could be right for you, complete our online eligibility check today.
