Study Links Medical Cannabis to Sustained Improvements in Endometriosis Symptoms

Endometriosis is a condition affecting around one in ten women of reproductive age, where tissue similar to the lining of the womb grows elsewhere in the body. It can cause severe pain, inflammation and, in some cases, fertility problems.

Participants completed questionnaires before starting treatment and again after one, three, six, 12, 18 and 24 months.

Researchers found improvements in measures of pain at every follow-up point, with improvements in sleep, anxiety and quality of life also sustained throughout the two-year period.

The study also found a reduction in prescribed opioids.

Average prescribed opioid use fell from the equivalent of 19.9mg of morphine a day at the start of the study to 14.8mg after two years.

Among the 46 participants prescribed opioids at some point during the study, 12 – around 26% – recorded what researchers considered a clinically meaningful reduction by 24 months.

Most patients were prescribed either cannabis oil or a combination of oil and dried cannabis flower.

Most patients were prescribed cannabis oil or a combination of oil and dried flower. At the start of the study, 33 received oil alone, 60 received flower alongside oil and eight received flower alone.

What were the side effects?

Eighteen of the 101 patients reported a total of 165 adverse events during the study, around half of which researchers classed as mild.

The most commonly reported were fatigue, lethargy and headaches.

However, the researchers stressed that the findings do not prove that medical cannabis caused the improvements.

The study was observational and had no control group, meaning other factors could have influenced the results. Patients were also prescribed different cannabis products and doses.

The authors said there have been no randomised controlled trials specifically examining cannabis-based medicines for endometriosis-associated pain and called for further trials to establish their effectiveness and safety.

Growing evidence around cannabis and endometriosis

The findings build on previous research into cannabis and cannabinoids for endometriosis.

A 2024 study led by Victoria Jasinski and researchers at Charité University Medicine Berlin, published in the journal Archives of Gynecology and Obstetrics, surveyed 912 people with endometriosis in Germany, Austria and Switzerland about how they managed their symptoms.

As Cannabis Health reported at the time, 114 respondents reported using cannabis, which they rated as the ‘most effective’ self-management strategy studied.

Among those using cannabis, 91% reported improved sleep, 90% reported improvements in menstrual pain and 80% in non-cyclical pelvic pain

But much of the evidence to date has relied on patient surveys and observational research rather than randomised controlled trials.

One such trial is now underway in Scotland. As Cannabis Health reported in March, the ENDOCAN Phase 2 trial, led by Dr Lucy Whitaker alongside Professors Andrew Horne and Philippa Saunders at the University of Edinburgh, is investigating Ananda Pharma’s MRX1 CBD oral solution in up to 100 women with endometriosis-associated pain.

The Chief Scientist Office-funded study, being carried out across NHS Lothian and NHS Grampian, is double-blind and placebo-controlled, with participants randomly assigned to receive either MRX1 or a placebo over 12 weeks.

Unlike the observational research to date, the trial is designed to provide stronger evidence on whether CBD itself can reduce endometriosis-associated pain.

Endometriosis and the wider unmet need in women’s health will be among the topics examined at the Cannabis Health Symposium London on 26 November.

Secure your place

The Cannabis Health Symposium London will take place at Conway Hall on 26 November 2026.

Find out more and book tickets here. Concessions are available for healthcare professionals by application.