Stewart said he often uses cannabis sprays, ointments and edible products to help soothe his arthritis, according to The Telegraph. The 76-year-old actor spoke out about his marijuana use to support a project from Oxford University that will explore the medical benefits of cannabis.

“Two years ago, in Los Angeles I was examined by a doctor and given a note which gave me legal permission to purchase, from a registered outlet, cannabis-based products, which I was advised might help the ortho-arthritis in both my hands,” Stewart said in a statement, according to Mashable. “This, it would seem, is a genetically-based condition. My mother had badly distorted and painful hands.”

The actor said he uses the ointment at night and applies the spray to his fingers and joints several times each day. The products have reduced the pain and stiffness in his hands, Stewart said in the statement, and even allowed him to make a fist, which he was previously unable to do.

Some politicians have said marijuana is “only slightly less awful” than heroin, but Stewart disagrees.

“I have had no negative side effects from this treatment and the alternative would have been to continue taking NSAID’s, Advil, Aleve and Naproxen, which are known to be harsh on the liver and to cause acid reflux,” Stewart said. “This is an important step forward for Britain in a field of research that has for too long been held back by prejudice, fear and ignorance. I believe this program of research might result in benefits for people like myself as well as millions of others.”