What is marijuana without the high? Still a very effective painkiller. And now, scientists believe they can harness the drug's anaesthetic action while doing away with its psychedelic effects. In a new paper published in the journal Nature Chemical Biology, Professor Li Zhang and a team of scientists at the U.S. National Institute on Alcohol Abuse and Alcoholism report that THC can potentially be used as a side-effect-free painkiller. Is a new class of "non-psychotropic cannabinoids" on the way? Here's a brief guide:

What is this breakthrough exactly?

Zhang and his team discovered that tetrahydrocannabinol (more commonly known as THC), the main psychoactive ingredient in cannabis, produces different effects by bonding to different receptors in the brain. Scientists have known for years that THC bonds with a certain receptor to produce the classic disorienting marijuana high. But now researchers have identified precisely where THC targets the nervous system to lessen anxiety and dull pain. Hence, the potential to satisfy medical marijuana's desire for pure pain relief.

How'd they figure this out?

By experimenting on mice, naturally. Scientists blocked the pain-reducing receptors in the stoned rodents' brains, then subjected them to a "tail-flick test" — hitting mices' tails with "focused heat" — and counted how long it took for them to respond. The fact that the mice still felt pain, even when they were dosed with THC, "confirms that the drug's pain-relief and psychotropic effects can be decoupled," says Andy Coghlan at The New Scientist.

So... THC pain pills?

Quite possibly. "Soon," says Annalee Newitz at IO9, "people whose stomachs are too tender for aspirin or ibuprofin may be swallowing THC pills to get rid of headaches."

Could another result be THC pills that do nothing but get you high?

It's the question recreational users will be pondering: "Is there a way to create a synthetic form of THC that does nothing but get you high, without all those pesky 'medicinal' side-effects?" asks Newitz at IO9. Stay tuned.

Sources: Nature Chemical Biology, New Scientist, I09, LA Weekly, Ars Technica