There is not enough evidence to promote medicinal marijuana as a safe choice for patients suffering with rheumatic conditions like rheumatoid arthritis, according to a new study.

The study published today in Arthritis Care & Research explores the risks associated with herbal cannabis used to such conditions.

"The effectiveness and safety of medical marijuana to treat symptoms of rheumatic conditions such as rheumatoid arthritis, lupus, or fibromyalgia is not supported by medical evidence," the study reads.

With ongoing changes in legalization and the public push for herbal cannabis therapy for pain management, Dr. Mary-Ann Fitzcharles, one of the study co-authors, says physicians need to be very aware of the health implications of the drug and dissuade patients with rheumatic conditions from using it.

"Our study aims to provide health care professionals with that medical evidence related to medical marijuana use in patients with rheumatic conditions,” she said.

"At this time, we cannot recommend herbal cannabis for arthritis pain management given the lack of efficacy data, potential harm from the drug, and availability of other therapies for managing pain… Physicians should discourage rheumatology patients from using medical marijuana as a therapy.”

The study acknowledges that there has been research on the efficacy of marijuana on pain management with other diseases, such as cancer or neuropathic pain – but adds that it cannot be assumed to work the same way in patients with rheumatic conditions, which have not had adequate study to date.

Higher THC levels in illegal marijuana

Another issue cited is that the concentration of tetrahydrocannabinol (THC) in illegal marijuana has typically doubled and often varies between two and 56 per cent without a way of estimating the dosing compound.

According to the researchers, a lot medicinal marijuana – despite being legal to use – may come from illegal means and if the concentration of THC is in the higher range there is a chance of more cognitive, physical and psychomotor effects.

Both acute and chronic risks were examined, including the problem with inhalation of the drug, the most popular way to take marijuana.

"Contrary to public belief, inhaled herbal cannabis is not innocuous," the study reads. "Risks can be categorized as the immediate effects on cognition, psychomotor function, cardiovascular effects and mood, and the chronic consequences on mental ability, pulmonary function, potential cancer risk and drug dependence."

Researchers also point out that common recreational users studied typically are younger and in better health than those using it for pain management and therefore can't be adequately compared.

They conclude that rheumatologists should promote further study into the use of marijuana with rheumatic patients where dosing can be controlled and safety can be assessed with a standard scientific method.