Marijuana is more popular and accessible in the U.S. than any other street drug. In national surveys, 48 percent of Americans say they have tried it, and 6.5 percent of high school seniors admit to daily use. So it was not too surprising when two states, Washington and Colorado, became the first to legalize recreational marijuana in the November 2012 general election, albeit in limited quantity, for anyone over the age of 21. Activists expect that similar measures will soon win approval in other parts of the country.
Some success with medical marijuana helped to pave the road to wider legalization of pot. Eighteen states and the District of Columbia permit possession and consumption of the drug for medical purposes. Doctors in those jurisdictions may prescribe cannabis to treat or manage ailments ranging from glaucoma—an eye disease in which the optic nerve is damaged—to menstrual cramps. Cancer patients sometimes smoke pot to relieve the pain and nausea brought on by chemotherapy, and some people with the inflammatory disease multiple sclerosis rely on marijuana to ease muscle stiffness.
Although many physicians agree that marijuana is safe enough to temporarily alleviate the symptoms of certain medical conditions, the safety of recreational use is poorly understood. Researchers worry that both the short- and long-term use of the drug may harm the body and mind. Marijuana's continued popularity among teenagers raises particular concern because the drug might hinder the ongoing maturation of the adolescent brain. Making matters worse, new growing techniques for the Cannabis sativa plant—from which marijuana is prepared—have dramatically increased the drug's potency. Some experts suggest that such high-octane weed is fueling a rise in cannabis addiction. Finally, although investigators still debate how the legalization of recreational marijuana will change road safety overall, studies indicate that the drug slows reaction time and impairs distance perception behind the wheel. Despite such evidence, most new marijuana regulations, for medical or recreational use, fail to account for these potential risks.
Whether rolled into a joint or mixed into brownie batter, marijuana profoundly changes behavior and awareness. The primary psychoactive compound in marijuana, tetrahydrocannabinol (THC), mimics the structure of molecules called endocannabinoids that the human body produces naturally. Endocannabinoids act on a group of cell-surface molecules called cannabinoid receptors that help to regulate appetite, mood and memory. Because of its shape, THC fits into these receptors, too. After all, jokes neuroscientist Giovanni Marsicano of the University of Bordeaux in France, “We don't have a receptor in the body just to smoke marijuana.”
When THC strikes specific cannabinoid receptors, it triggers domino chains of interacting molecules in neurons that culminate in both unusually elevated and abnormally low levels of various neurotransmitters (the molecules that brain cells use to communicate with one another). The result is the well-known “high” of marijuana. Suddenly, the mundane seems hilarious, and ordinary foods taste delicious. People generally feel merry, relaxed and introspective, although undesirable effects—such as paranoia and irritability—are common as well.
Marijuana also temporarily impairs an array of mental abilities, especially memory and attention. Dozens of studies have shown, for example, that people under the influence of marijuana perform worse on tests of working memory, which is the ability to temporarily hold and manipulate information in one's mind. Participants in these studies have greater difficulty remembering and reciting short lists of numerals and random words. Research has further revealed that cannabis blunts concentration, weakens motor coordination and interferes with the ability to quickly scan one's surroundings for obstacles.