PAIN triggers the release in the brain of a chemical similar to the active ingredient of marijuana, according to a study that will aid the development of painkillers and supports the medical use of cannabis, writes Roger Highfield.

This is the first time that the role of the drug - a cannabinoid known as anandamide - in the brain's pain response system has been documented.

The findings are published today in the Proceedings of the National Academy of Sciences by Prof Michael Walker and colleagues at Brown University, Providence, Rhode Island.  The discovery was not unexpected: cannabinoids have been used to treat pain for centuries.

However, the detailed knowledge will be valuable for the future treatment of pain, particularly when conventional drugs such as opiates are found to be ineffective.