It seems like an oxymoron that a drug that gives you the munchies could also be controlling your blood sugar level, but that's what researchers at Harvard School of Public Health and Beth Israel Deaconess Medical Center in Boston found in a study of more than 4,500 adults. Their findings were published in The American Journal of Medicine earlier this year.

Medicalmarjuananeon

Source: Chuck Coker, Flickr.

Current users of marijuana had lower levels of insulin after fasting and lower insulin resistance than nonusers. Both laboratory tests are risk factors for developing diabetes. Adjusting for body mass index, marijuana users also had smaller waist circumferences than their nonuser counterparts.

Before you sell stock in your diabetes-drug makers -- or put down your diabetes medication and pick up a bong -- read on; the association isn't clean enough to be worried about sales in Merck's (NYSE:MRK) Januvia or Novo Nordisk's (NYSE:NVO) franchise of diabetes drugs just yet.

Unknown effect
Exactly why you'd see the correlation isn't clear. It's possible that the marijuana is stimulating not only the user's appetite, but also his or her metabolism, thus burning the increased caloric intake. Perhaps you can have your cake and eat it, too.

Another possible explanation: As tolerance to marijuana builds up from repeated marijuana use, the receptor that marijuana stimulates, which makes the user hungry, might become desensitized. The body produces molecules similar to those in marijuana that stimulate appetite through the same receptor. If the receptors are less sensitive, the body's natural appetite stimulation would be reduced.

And data from this report can't rule out the possibility that the observed effect has nothing to do with marijuana use at all. The researchers factored in differences such as age, sex, income, alcohol use, cigarette smoking, and physical activity when determining if there were differences in insulin levels, but it wasn't a prospective controlled clinical trial; people in the trial self-reported their marijuana use after the fact. There could be some other factor that is common among marijuana users that is actually causing the effect on insulin levels.

A cleaner trial
A better way to study the effects of marijuana would be to start with nonusers -- give half marijuana and half a placebo and look at the effect on insulin and other factors. But that's not easy to do, since there isn't a good placebo for marijuana. It's kind of obvious if you're not getting buzzed that you must be in the placebo group, which defeats the purpose of a double-blind trial.

You could run what's called an open-label trial, where researchers and patients know who is getting the drug and who is in the control group. That kind of prospective trial would still be better than the retrospective trial from these findings, but apparently it isn't easy to get approved for a trial where patients are given marijuana, since it's still an illegal substance on a national level.

Further exploration
No matter what your feelings on the legalization of marijuana, the findings are enticing enough to justify further exploration. Merck, Novo Nordisk, or one of the other diabetes drug makers could figure out the mechanism that marijuana uses to control insulin levels and then develop a drug that mimics the response without the buzz associated with marijuana.

For instance, if the receptor sensitivity theory turns out to be correct, it might be possible to develop a drug that leads to the same effect, thus sedating appetite, which might be used as a treatment for obesity or diabetes prevention for those at risk.

Rather than building tolerance, Sanofi's (NYSE:SNY) obesity drug Acomplia blocked the receptor, which controlled patients' appetites but also caused psychiatric side effects, including making users depressed. Acomplia never made it to market in the U.S. and was eventually pulled from the shelves in Europe.

A drug that decreases receptor sensitivity might cause the same side effects as Acomplia did blocking it, but there's no way to know for sure unless some drugmaker steps up and develops a drug.

Fool contributor Brian Orelli and The Motley Fool have no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.