Medical marijuana might help ease chronic pain, but it also slightly increases a patient’s risk of a dangerous abnormal heart rhythm, research says.

Patients treated with medical cannabis had a nearly 1 percent increased risk of being diagnosed with a heart rhythm problem that required monitoring and possible treatment.

Researchers tracked 5,400 Danish patients who were prescribed cannabis for chronic pain. They were compared with nearly 27,000 chronic pain patients not using cannabis as a treatment. Patients using medical weed had a 0.8 percent risk of being diagnosed with a heart rhythm problem, researchers found.

That’s more than twice the odds of someone who wasn’t taking the drug.

The largest increases in risk occurred among people 60 or older, as well as those already diagnosed with a chronic condition such as cancer, heart disease, stroke, or diabetes.