People taking medical cannabis for chronic pain have a slightly increased risk of arrhythmia, according to research published in the European Heart Journal.

Researchers say the new study is important as a growing number of countries now permit medical cannabis as a treatment for chronic pain.

The study was led by Dr Anders Holt from Copenhagen University Hospital – Herlev and Gentofte in Denmark. 

The study included data on 5,391 Danish patients who had been prescribed cannabis for chronic pain.

This included people with pain in their muscles, joints or bones, people with cancer and those suffering with nerve pain. Researchers compared this group with 26,941 patients who also had chronic pain but were not receiving cannabis as a treatment.

The data showed that patients receiving medical cannabis had a 0.8% risk of being diagnosed with arrhythmia that required monitoring and possible treatment within 180 days of receiving cannabis. This risk was more than twice that of patients with chronic pain who were not taking cannabis. 

The difference in risk between the two groups had become smaller when researchers looked at the first year of treatment.

Patients taking cannabis who were aged 60 and older and those already diagnosed with cancer or cardiometabolic disease, such as heart disease, stroke and diabetes, had the largest increases in their risk of arrhythmia.

The study did not show any link between taking medical cannabis and the risk of acute coronary syndrome.

Dr Holt said: “Medical cannabis is now allowed as a treatment for chronic pain in 38 US states as well as several countries in Europe and elsewhere around the world. This means more and more doctors will find themselves prescribing cannabis, despite a lack of evidence on its side effects.”