FILE PHOTO: An employee sorts harvested cannabis buds at Hexo Corp's facilities in Gatineau, Quebec, Canada, September 26, 2018. REUTERS/Chris Wattie

LISBON (Reuters) - Evidence is still thin on the benefits of medicinal use of cannabis, an EU agency that monitors illegal drugs and addiction said on Tuesday, urging more study into the topic as growing numbers of countries allow it.

The Lisbon-based EMCDDA said in its first report on the topic that so far there were “important gaps in the evidence”.

A handful of regulated pharmaceuticals use chemicals derived from cannabis, such as GW Pharmaceuticals’ Sativex which is approved for treating symptoms of multiple sclerosis. But cannabis itself and most products made from it are governed by countries’ individual criminal laws on illegal drugs, which may or may not allow medicinal use.

Medical marijuana has been legal in some U.S. states and Canada since the 1990s. Within the EU, it is allowed in countries including Germany, Italy, Denmark, Portugal and the Czech Republic. Britain decided in July to allow it.

The EMCDDA said there was a “need for additional research and clinical studies, including larger and better-designed trials, studies looking at dosage and interactions between medicines, and studies with longer-term follow-up of participants”.

It found “moderate” evidence that cannabis helped patients suffering from muscle spasms due to multiple sclerosis, chronic non-cancer pain and epilepsy in childhood.

Evidence for cannabis providing relief for patients with nausea and vomiting due to cancer chemotherapy or as an appetite stimulant for AIDS sufferers was “weak”, and evidence for use in patients with post-traumatic stress disorder, sleep disorders and anxiety disorders, was “insufficient”, it said.

The “evidence base (for medical cannabis) is evolving rapidly but is currently quite limited and fragmented, which needs to be borne in mind when considering any evidence review,” it said.