Reverse engineering the marijuana 'munchies:' What causes binge eating?

How could both marijuana and a compound that has the opposite effect of pot act on the same brain receptors and lead to weight loss?

Natural marijuana includes many different potentially active compounds, and one of them -- rather than THC -- could be responsible for this effect. One potential candidate is a substance called cannabidiol, which also affects cannabinoid receptors, but in a different way from the way THC or rimonabant does.

Another possibility involves tolerance: repeated use of a drug can make receptors less sensitive over time. "The most likely explanation is that prolonged cannabis use causes the (receptors) to lose sensitivity and become inactive," says Daniele Piomelli, a professor of pharmacology at the University of California, Irvine, who was not associated with the new research.
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"This has been shown to happen in people who smoke marijuana. This weakening of (these receptors) translates into a lower risk for obesity and diabetes because the inactive receptor would be unable to respond to our own cannabis-like molecules, which we know are important in keeping us chubby."

While marijuana may initially promote appetite and overeating, in the long run it has the opposite effect because it desensitizes cannabinoid receptors and may even protect against obesity.

So don't skip the gym and break out the bong just yet: there's still not enough data to tell whether marijuana, like alcohol, could have health benefits in moderation. Mittleman says the study relied on self-reported use of marijuana, which can be unreliable. However, he points out that since people are more likely to hide drug use than they are to falsely claim it, the findings could even underestimate marijuana's effects.

But whether that's true, and whether marijuana might be a window into understanding how to best control glucose and insulin to prevent diabetes, isn't known yet.

"It is much too early to say," says Mittleman. "We need much more research to better understand the biologic responses to marijuana use. We really need more research to allow physicians and patients to make decisions based on solid evidence." An editorial that accompanied the study also urged government action to reduce barriers to such research.

Even with 18 states now approving marijuana for medical uses, the politics of pot will always overshadow research efforts to understand how cannabinoids work in the brain -- or affect disease. But, as Piomelli says, "the (new) study suggests that smoking marijuana (may) protect people against obesity and diabetes." And following up on that finding could yield new insights into how to tackle one of our biggest public-health issues.