Placebos Use Pot Receptor

Some pain-relief placebos work in part by activating a cannabinoid receptor, stimulating the same pathway as marijuana.

Oct 5, 2011
Tia Ghose

FLICKR, E-MAGINE ART

It’s well known that a placebo can relieve pain, but how such non-active ingredients can have such a positive effect has long stumped scientists. Now, new researchers suggests that placebos may help ease a patient’s pain by activating cannabinoid receptors, which are also targeted by marijuana, according to a study published October 2(Sunday) in Nature Medicine.

Researchers can give subjects an opioid prior to wrapping their arm with a painfully tight tourniquet. Thereafter, volunteers can tolerate pain longer when given a placebo instead of drugs on follow-up days, presumably because they’ve been primed to expect pain relief from the drug. Nonsteroidal anti-inflammatory drugs (NSAIDs) such as iburprofen can also be used as a primer to induce this placebo-pain relief effect.

In the new study, researchers gave volunteers an NSAID prior to a painful stimulus, followed by rimbonant, which blocks the activation of a cannabinoid receptor, on subsequent days.  Volunteers who received rimbonant on the placebo days experienced no pain relief,  suggesting that part of the placebo effect was working via the cannabinoid pathway, and that blocking the pathway abolished the effect, Wired Science reported. When researchers combined rimbonant with an opioid, the placebo still quieted pain, suggesting that the opioid placebo effect works through a different mechanism.