How does smoking marijuana make you hungry? Does it speed up the metabolism?

Thanks to http://www.mc.maricopa.edu/other/legend/ARCHIVES/vol38issue13/news8.htm :

Recently, scientists in Italy have discovered more about the mechanisms that make marijuana users hungry, as well as what makes humans hungry in general.

The operative molecules are called endocannabinoids, and they have receptors in the brain that, when activated, increase the appetite of the subject.

The researchers’ results, published in last week’s scientific journal Nature, have potential uses for dieting programs and medications.

"There is tremendous interest in marijuana because of some of the unique physiological effects it has," UW biochemistry professor Dr. T.F. Martin said. "It has been useful in pain killing, glaucoma treatment, etc. and in all of this, it is possible that an appetite-suppressing drug may be found, which is a billion-dollar-a-year industry."

To decipher the effects of endocannabinoids, the researchers genetically altered mice, removing the endocannabinoid receptors in their brains.

Once they had created these "knockout mice" and monitored them, they found that the mice ate less than the control mice.

To further study the effects of endocannabinoids, the researchers also gave ordinary mice a drug that blocked endocannabinoids from acting on the receptors in the brain. These mice also ate less than the control group.

"Marijuana produces a multitude of effects – euphoria, analgesia, etc.," Martin said. "It is believed that the majority of these are produced because delta-nine-tetrahydrocannabinol in marijuana can bind to CB1 receptors in the nervous system and mimic endogenous cannabinoids."

The study also hypothesizes that endocannabinoids are part of the complex neural circuitry controlled by a hormone called leptin, which tells the brain when it is time to lose weight.

"These findings indicate that endocannabinoids in the hypothalamus may tonically activate CB1 receptors to maintain food intake and form part of the neural circuitry regulated by leptin," the study said.

Even though the researchers know what hormone to control to encourage weight loss, it would be difficult to develop a drug based on cannabinoids alone.

"The endocannabinoid receptors such as CB1 are very widespread in the central nervous system," Martin said. "Cannabinoids have effects on memory, cognition, coordination, mood, pain sensation, sleep and appetite.

Since these effects seem to be mediated largely by a common receptor, using a drug to block this receptor may have many consequences." Martin said.