Part of placebo effect ascribed to cannabinoids [View All]

[n2doc]

By Jonathan M. Gitlin | Published about an hour ago

In clinical trials, new drugs are often compared to older treatments, but sometimes they're also compared to placebos—inert treatments that ought to have no effect. Except that's not what happens. The placebo effect can actually be pretty strong, and even more strangely, placebos can work even when the patient knows they're being given one.

Most of what we know about placebos results from studies on how we process pain, since it's more ethical to give someone a placebo instead of a painkiller than it would be to replace an anti-cancer drug or insulin. Some of the analgesic (painkilling) effect of placebo treatment is due to endogenous opioids, ones made by the body. Now, evidence has emerged that suggests an additional effect results from the cannabinoid pathway, according to a publication in Nature Medicine.

Placebo-activated opioid analgesia doesn't work all the time. Experimentally, researchers can induce it by preconditioning a research subject with an actual opioid analgesic. Or, to explain that in plain English, you give the subject a painful stimulus then give them an opioid to treat it. You do this several times then, instead of giving them a real drug, you give them a placebo, which will block the pain. What's more, you can actually inhibit the action of the placebo by giving the subject an opioid antagonist like naloxone, which blocks the effect of opioids. Still with me? Good.

Here's where things get more complicated. You can also use a nonsteroidal anti-inflammatory (NSAID), like ibuprofen, to create a placebo analgesic effect. But this time, it can't be blocked with naloxone. So there's more than one biochemical pathway responsible for the analgesic effects of sugar pills. The new paper involves an attempt to look for alternate pathways.


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http://arstechnica.com/science/news/2011/10/is-the-placebo-effect-partially-caused-by-cannabinoids.ars