A new study has highlighted the effectiveness of cannabinoid compounds found in cannabis for pain relief in women suffering with endometriosis, leading to a clinical trial launching in Spain.

Endometriosis is a painful condition where the lining of the uterus grows on other parts of the organ such as the fallopian tubes. The new study, published in eLife, shows initial results from treating endometriosis in mice with cannabinoids – suggesting they can alleviate symptoms of the disease.

The researchers say this new finding will pave the way for further clinical research.

The findings have led to the start of a clinical trial in collaboration with the Gynecology Service of the Hospital Clinic of Barcelona, Spain. The trial will evaluate the possible benefits of the naturally occurring cannabinoid ∆9-tetrahydrocannabinol (THC; the main psychoactive constituent of the cannabis plant) in women with endometriosis.

Endometriosis cannabis treatment

Endometriosis is a common, chronic and painful disease caused when the lining of the womb – the endometrium – grows outside of the womb cavity. These growths affect reproductive organs and can cause pain, infertility, anxiety, depression and result in a considerable impact on quality of life. Treatment options include surgery or hormone therapy, but these are not always effective and often have significant side-effects.

Rafael Maldonado, Professor at the University Pompeu Fabra of Barcelona, Spain, said: “With a lack of effective treatments, women with endometriosis usually rely on self-management strategies like dietary changes or exercise. Although cannabis comes with a large number of potential side effects, its medicinal properties could provide pain relief in endometriosis and other conditions.

“Since medical THC is available in some countries, the findings of our study may be of interest for gynecologists and pain specialists who manage the treatment of women with endometrial pain.”

THC improves symptoms and growths

The team studied mice with endometrial implants in their pelvis to mimic endometriosis in humans. Those with the implants were more sensitive to pain in their pelvis that can also be associated with emotional and cognitive alterations – similar to symptoms seen in some women with endometriosis.

The team next found that mice with endometriosis had similar anxiety-like symptoms experienced by some women with the condition. This was measured by the amount of time the animals spent in open areas of a maze, as those with higher anxiety levels tend not to explore too far. However, their experiments could not reveal whether THC had any significant effects in treating this anxiety.

As endometriosis can be known to impair cognitive function in some women, the team also studied memory performance in the mice. They provided the animals with two identical objects and allowed them to become familiar with them. They then replaced one of the objects and timed how long the mice spent exploring the new versus familiar object, to give an indication of what the animals remembered.

The team found that memory was impaired in the mice with endometriosis compared with those that did not have the condition. However, mice treated with THC did not show this impairment, suggesting that THC may have a protective effect.

Finally, the team studied the effects of THC on the endometrium inside and outside of the womb, and found that mice with endometriosis treated with THC for 32 days had smaller endometrial growths.

First author Alejandra Escudero-Lara, a PhD student at the University Pompeu Fabra of Barcelona, said: “Together, our findings show that THC limits the development and symptoms of endometriosis in an experimental model, and highlight the interest of conducting further research to ensure the safety and beneficial effects of this treatment in women with endometriosis.”