Marijuana consists of the leaves, flowers, and buds of the hemp plant (Cannabis sativa and also Cannabis indica). The active ingredient in marijuana is the chemical delta-9-tetrahydrocannabinol (THC), which can be introduced into the body in a variety of ways—dried and then smoked, for example, or eaten. The THC can also be concentrated into a form known as hashish. In all cases, marijuana has a range of effects: It relaxes the user, lifts her mood, and (like alcohol) reduces the ability to resist impulses. It also heightens sensations, so it can be considered a mild hallucinogenic.
Like most drugs, marijuana’s effects depend on the context, including the user’s expectations. If you’re surrounded by giggly friends, marijuana is likely to make you giggly as well. If you’re alone and anxious, marijuana can magnify these feelings as well.
Marijuana has various therapeutic uses. For many years, it was the best way to control the pain from glaucoma or the nausea from chemotherapy. (Other, more reliable, medications have now been developed for these purposes.) Marijuana also seems to be effective in treating the pain and general discomfort associated with several other medical conditions, including AIDS. This is why marijuana is prescribed for medical use in roughly a dozen U.S. states, although each state places its own restrictions on how and by whom the marijuana can be acquired and used.
The risk of addiction or dependence is low for marijuana. Infrequent users seem to suffer few withdrawal problems if they stop using the drug altogether. For more frequent users (e.g., multiple marijuana joints per day), quitting has been shown to produce with-drawal symptoms similar to those of tobacco users when they stop smoking. These symp-toms may include sleep difficulties, increased anxiety, and irritability.
In addition—and despite claims to the contrary—marijuana doesn’t seem to be a “gateway drug” that leads people to try (and eventually abuse) more potent drugs (Hart, Ksir, & Ray, 2009). There’s also little reason to believe the media reports suggesting that marijuana has a long-lasting impact on sexual functioning or fertility (Grinspoon, Bakalar, & Russo, 2005).
Even so, many problems are associated with marijuana use. Marijuana smoke contains cancer-causing substances; in fact, it contains more of these substances than tobacco smoke does. Marijuana intoxication can also undermine a user’s judgment, diminish motor coordination, and increase reaction time (Lane et al., 2005)—and so people under the influence of marijuana should certainly not drive or make big decisions of any sort. Marijuana also seems to interfere with memory—both the creation of new memories as well as the recall of older ones—and these effects seem to persist even when the immedi-ate drug effects have worn off (Pope, Gruber, & Yurgelun-Todd, 2001).
How exactly does THC affect the brain? Evidence suggests that this molecule latches onto receptors located especially in the midbrain and in various limbic structures (Devane, Dysarz, Johnson, Melvin, & Howlett, 1988); it seems that all vertebrates may have these cannabinoid receptors (Elphick & Egertova, 2001; van Sickle et al., 2005).
These results raise a question, though: Why should the body have receptors that are responsive to THC at all? The answer seems to be that these cells are normally activated by a neurotransmitter called anandamide (from the Sanskrit word ananda, meaning “bliss”). This transmitter is chemically similar to THC, but it’s produced naturally in the body (Devane et al., 1992; Wiley, 1999). Ordinarily, it seems to be involved in a range of functions including mood regulation, appetite control, and pain perception. Marijuana may have its effect, therefore, by triggering some of the same mechanisms.
It turns out that other chemicals also bear some resemblance to anandamide and so may mimic some of its effects. One such chemical is found in chocolate—which may be part of the reason so many people enjoy eating chocolate.