A new pain-suppressing drug that works by an unusual mechanism is described online in Nature Neuroscience this week.

The cannabinoid type 1 (CB1) receptor — which is known to mediate the effects of marijuana — also recognizes the body’s own endocannabinoids. CB1 receptors are found both within the central nervous system (CNS) and the peripheral nervous system. Drugs that target the components of the endocannabinoid system produce pain relief. However, in addition to providing pain relief in the periphery, most drugs targeting the endocannabinoid system readily penetrate the blood-brain barrier, entering the brain and leading to undesirable CNS side effects, such as a risk of increased drug or alcohol abuse in susceptible individuals.

Daniele Piomelli and colleagues have developed a molecule that activates CB1 only outside the brain and spinal cord. The drug, with the code name URB937, inhibits an enzyme that degrades one of the endocannabinoids, known as anandamide. In rats, the scientists found that this drug elevated anandamide levels, increased CB1 activation and consequently alleviated several kinds of peripheral pain. URB937 entered the brain, but unlike other CB1 activators, was quickly recognized and pumped out of the brain by a specialized transporter molecule. Therefore URB937 did not affect anandamide degradation in the brain and therefore is unlikely to produce any unwanted side effects.

As URB937 suppresses pain by a mechanism that is completely different from existing painkillers, it, or its derivatives, may in future be useful for pain management.