Researchers in the United States have found that a cannabis like chemical produced naturally in the brain helps with pain relief.
They say the finding may lead to new drugs which can stimulate this natural response.
Research has so far concentrated on developing compounds in cannabis itself into medications, but this study shows for the first time that natural marijuana-like chemicals in the brain have a link to pain suppression.
The US scientists say their new understanding of how the brain chemical works could lead to drugs with fewer side-effects.
Professor Danielle Piomelli, director of the Center for Drug Discovery at the University of California, Irvine, says that when the body experiences pain under stressful circumstances, such as an injury during sport or even after a gunshot wound, the body is protected for a period of time.
This response is called stress-induced analgesia.
In a study in rats the team found, for the first time, how chemicals called endocannabinoids play a part in this process.
The production of one cannabinoid compound, 2-AG, was found to be triggered by stress-related pain, so the researchers then looked at ways of boosting this natural response.
As an enzyme called monoacylglycerol lipase normally brings the production of 2-AG to a halt, the team, developed a chemical which was able to block the enzyme's action, meaning the body could theoretically continue to keep producing 2-AG.
Professor Piomelli says the study shows for the first time that natural marijuana-like chemicals in the brain have a link to pain suppression, and apart from identifying an important function of these compounds, it provides a template for a new class of pain medications that can possibly replace others shown to have acute side effects.
Piomelli says if chemicals can be designed that can tweak the levels of these cannabinoid compounds in the brain, it might be possible to boost their normal effects.
Dr Andrea Hohmann, a neuroscientist at the University of Georgia, who also worked on the research, says as yet there is no prescription or over-the-counter drug that allows us to manipulate the level of the brain's compounds.
She says this is the first time anyone has shown that one of the body's natural occurring cannabinoids, 2-AG, has anything to do with pain regulation under natural conditions.
Dr Anita Holdcroft, a reader in anaesthesia at Imperial College, says the study adds to knowledge about how the body deals with pain.
The study is published in the current edition of Nature.