Current lawmakers make frown on cannabis use, but for thousands of years people used it to treat conditions as diverse as rheumatism, convulsions, tumors, and pain. Now the small, private UK company Oxford Natural Products has completed Phase I trials on a cannabis derivative for treating post-operative and cancer pain.

ONP-04 is a pro-drug-an inactive substance that converts to the active form in the body-of tetrahydrocannabinol (THC), a major active ingredient of cannabis, formulated as a suppository. The Phase I trial, carried out by Inveresk Research, showed that delivering the product through a suppository increased bioavailability, with steadier release of the active ingredient. It also caused less liver damage than the US-licensed oral THC product, Marinol. A further advantage of rectal over oral administration is that it is much easier to administer to cancer patients, who often experience serious nausea and vomiting.

ONP licensed the active ingredient, THC hemi-succinate, from the University of Mississippi, which is the only legal producer of cannabis in the United States. ONP is now looking for a development partner to advance the medicine to Phase III.