There is not enough reliable evidence to say whether medical cannabis helps people with insomnia, according to a new Cochrane review. The findings were reported by ScienceDaily, which drew on material provided by Cochrane.

Researchers from the Cochrane Associate Centre at the Universidad Hospital Italiano de Buenos Aires and the University of Manitoba examined nine clinical studies involving 537 adults aged between 18 and 76 who were being treated for insomnia. They looked at sleep quality, satisfaction with sleep, total hours slept and how well people functioned during the day.

What the review found

Most of the studies involved people with primary insomnia, meaning their sleep problems were not attributed to another medical condition. Eight trials compared regulated medical cannabis with a placebo. The other compared it with amitriptyline, an antidepressant sometimes used for sleep problems.

In the placebo comparisons, medical cannabis produced little or no clinically meaningful improvement in sleep quality, sleep satisfaction, total sleep time or daytime functioning.

People given medical cannabis were substantially more likely to report mild side effects, including dizziness and dry mouth, than those given a placebo. The reviewers noted that this came from a relatively small number of studies, which limits confidence in the result.

There was some sign that quality of life might improve, but the evidence was highly uncertain. The combined results were consistent with anything from a slight decline to a substantial improvement.

Why the evidence is weak

The reviewers rated their confidence in the evidence as low or very low. They cited small numbers of participants, conflicting findings and potential bias in how some trials were run.

The studies also tested different medical cannabis products, which made direct comparison difficult. The longest followed participants for only 12 weeks, so it is unknown whether any benefit would last or whether longer use might bring other effects.

The participants were not representative of everyone with insomnia. Women made up 72.66% of the total, and the research leaned towards younger adults. It is therefore unclear whether the results apply equally to men, older people or those whose insomnia occurs alongside other conditions.

“The main message is that the research currently available is not sufficient to reliably answer whether medical cannabis helps people with insomnia.”

That is according to lead author Dr Lucia Varela of the University of Manitoba. She added: “This does not mean that medical cannabis is ineffective.”

Senior author Dr Luis Garegnani, of the Universidad Hospital Italiano de Buenos Aires, said clinicians and patients should recognise the uncertainty and consider individual circumstances while better evidence is generated. The authors say larger, more rigorous trials are needed before medical cannabis can be confidently recommended for sleep.

Context for UK readers

Specialist doctors in the UK have been able to prescribe cannabis-based medicines since 1 November 2018. NHS prescriptions remain rare, and most patients use private clinics. Insomnia is among the conditions for which some people seek such prescriptions, so the review’s conclusions about the limits of the current evidence are relevant to UK patients and clinicians.

The review is not medical advice. People with sleep problems should speak to a doctor or pharmacist about treatment options.