"MDA19 has the potential for alleviating neuropathic pain without producing adverse effects in the central nervous system," said Dr Mohamed Naguib of The University of Texas.

Dr. Naguib investigated cannabinoid receptors to develop new drugs that could treat neuropathic pain.

Neuropathic pain is caused by nerve damage and is common in patients with trauma, diabetes, and other conditions.

Current treatments are generally ineffective.

Rats treated with MDA19 experienced reduced neuropathic pain, with greater effects at higher doses.

At the same time, it did not seem to cause any of the behavioural effects associated with cannabis.

"With functionally selective drugs, it would be possible to separate the desired from the undesired effects of a single molecule through a single receptor," Dr Naguib said.

More research will be needed before MDA19 is ready for testing in humans.

"These elegant studies by Professor Naguib demonstrate remarkable analgesic properties for this synthetic cannabinoid," said Dr Steven L. Shafer of Columbia University.

"Although preliminary, these studies suggest that synthetic cannabinoids may be a significant step forward for patients suffering from neuropathic pain."