I know that this really isn't the type of thing that is asked about frequently, but I gotta ask. When someone smokes marijuana, they get the much-fabled "munchies." I know that this occurs, I am just at a loss as to why it does occur. What is the physiological reasons for this to occur?
You need to slack off on the ganja, bro. What you meant to ask was what the physiological reasons are. Also, you used "occur" three times in two sentences. Besides interfering with cognitive function, marijuana impairs short-term memory. Looks like yours can be measured in milliseconds.
Last time the subject of the munchies came up, in 1977--I've been writing this column longer than a lot of you sumbitches have been alive--all I could tell you was that scientists had ruled out dope-induced fluctuations in blood sugar as a cause. Since then, I'm pleased to inform you, great strides have been made. As it turns out, far from being a mere curiosity, the munchies provide a clue to the workings of one of the body's primary methods of hunger regulation, the endogenous cannabinoid system.
Your body, it seems, contains specialized proteins called cannabinoid receptors. (Broadly speaking, receptors react to certain stimuli and produce certain results.) The best-known cannabinoid is delta 9-tetrahydrocannabinol or THC, the principal psychoactive ingredient of weed (aka cannabis). Far more important from the body's standpoint, however, are the endogenous (i.e., internally synthesized) cannabinoids, endocannabinoids for short, which work like neurotransmitters and are produced as part of the built-in apparatus by which peripheral parts of the body inform the brain that it's lunchtime. Endocannabinoids and cannabinoid receptors are abundant in the hypothalamus, the region of the brain that plays a pivotal role in appetite regulation. In 1992 researchers identified the first endocannabinoid and named it anandamide, from the Sanskrit ananda, meaning inner bliss. In other words, when you smoke dope, you're replicating (albeit with much greater intensity) an effect the body produces naturally for itself.
Hunger regulation isn't the only thing endocannabinoids do for the body. Though their action is still imperfectly understood, a 1998 research paper suggests that they help you "feel less pain, control your movement, relax, eat, forget, sleep and protect" yourself against stress. In fact, some scientists think they're an important part of the body's general stress-recovery system.
The significant role of cannabinoids in body chemistry has created great excitement about the therapeutic use of THC and related compounds. The most obvious beneficiaries are people who've lost the desire to eat--for example, late-stage cancer or AIDS patients. (In India, in fact, folks have used pot to treat loss of appetite since around 300 AD.) Though research is incomplete, it appears that (a) smoking marijuana is the best means of administering THC; (b) food consumption increases primarily in social settings; and (c) the foods consumed tend to be sweet. So it's possible that someday the recommended treatment for disease-induced anorexia may consist of lighting up a few joints, sitting around in a group, and munching Oreos. Lest you get the wrong idea, though, appetite-suppressed patients don't necessarily have to get high to enjoy the benefits of marijuana. At the lowest effective dose, test subjects report little or no euphoria, sleepiness, or dizziness.
Cannabinoids have a variety of other medical applications. The use of marijuana in the treatment of glaucoma is well-known. THC, under the name Dronabinol, has been used since 1985 to ease the nausea and vomiting caused by chemotherapy. Cannabinoid antagonists, which inhibit the effects of cannabis-type compounds, have been shown to suppress sugar and alcohol consumption in lab animals and are thought to hold great promise for obese humans, particularly those with a weakness for sweets.
While I'm not pointing any fingers, I'll bet that much of the research on cannabinoids has been conducted by investigators who were toking up in their dorm rooms 30 years earlier, which goes to show that vice can have its usefulness. Here our parents thought we were frivoling away our lives. Ha. We were on the frontiers of science.