Technically, marijuana is not a drug, but a vegetable substance that contains a whole series of chemicals. What is sold on the street as marijuana in the United States are the dried leaves and flowering tops of the plant Cannabis saliva or, less commonly, Cannabis indica. The cannabis plant contains hundreds of chemicals; sixty-one of them, called cannabinoids, are found nowhere else. The primary psychoactive agent in marijuana is transdelta-tetrahydrocannabinol, or THC. It is generally agreed that it is the THC that gets the user high. Different batches of marijuana contain varying proportions of THC. Analyses of street samples of marijuana indicate that the THC content of marijuana has been rising; during the 1960s and early 1970s, between 1 and 2 percent THC for a batch of commercial-grade Mexican marijuana was typical.

Today, marijuana, imported mainly from Colombia, contains about 4 percent THC. Varieties specially grown without seeds, from California and Hawaii, called sinsemilla (meaning "without seeds" in Spanish), contain more than 6 percent THC. Hashish contains the resin of the marijuana flower with no leaves, and usually has a higher THC content than marijuana. Hashish usually comes from Asia and the Middle East; it is rarely available in the United States nowadays, although it is common in Europe.

One feature of marijuana that makes it different from alcohol as a recreational drug is that, while alcohol passes through the body fairly quickly, THC is stored in the body, specifically in the fatty tissue, for long periods of time. The half-life (the period of time after use when half the chemical is still in the body) of THC in the blood is nineteen hours, but its metabolites have a half-life of fifty hours. After one week, 25 percent of THC's metabolites remain in the body . The slow rate of the elimination of THC and its products suggests that if it is used regularly, some storage and accumulation take place, which may be medically harmful to the user. In addition, marijuana is usually smoked, perhaps in 95 percent of all episodes of its use in the United States. Taking the fumes of any combusted substance into the lungs is likely to have a number of medical consequences not characteristic of a drug taken orally, as any student of cigarette smoking will tell you.

The first and most fundamental fact about marijuana use in the United States that needs to be emphasized is that it is pervasive, very nearly universal, among young Americans. This does not mean that every adolescent and \ oung adult uses it, only that it can be found practically everywhere. Nor does it mean that all who use it do so equally often; clearly, frequency of use is a variable, not a constant. Still, nearly all adolescents have to come to terms with the drug. This makes it necessary for teenagers "to confront choices and decisions about whether, when, and how to use." So much is this the case that at least one observer argues that it is futile for parents, educators, and authorities to expect to eliminate the use of the drug among youth completely. It makes more sense, he argues, to attempt to reduce or delay its use, and to encourage young people to use it, if they insist on doing so, responsibly, moderately, and in relatively safe contexts. (Naturally, this approach has its critics; see Mann, 1987.)

It is true that marijuana use has declined during the 1980s—which is also true, as we have seen, of all other illicit drugs (except cocaine), and cigarettes and alcohol as well. Some observers have contended that marijuana use is passe, that the use of other drugs is more common, that cocaine has become more popular than marijuana. These claims are simply journalistic exaggeration and sensationalism. In fact, according to every reliable, systematic survey that has ever been conducted on the subject, marijuana has been, and is now, the most commonly tried or used illegal drug in the country, and it is likely to remain so.

Even when other drugs are taken, marijuana is very often used in conjunction with them. In the 1982 national household survey sponsored by the National Institute on Drug Abuse , it was found that: "In every age group, the majority of those who have ever used cocaine say that they have used marijuana on the same occasion that they took cocaine." Thus the use of other illegal drugs usually also implies marijuana use, although the reverse is not necessarily true.

As we saw in the 1985 nationwide survey sponsored by NIDA, a third of the American population age 12 and older has tried marijuana—some 62 million individuals. And one in ten, a total of some 18 million Americans, are "current" users—that is, have used the drug within the past month (NIDA, 1986). Among high-school students, much the same picture prevails: Marijuana is common—in fact, the most frequently used illegal drug. Just over half (51 percent) of the country's high-school seniors have used marijuana at least once, and nearly a quarter . There are three times as many individuals who have used marijuana as have used cocaine, and almost four times as many current users of marijuana as of cocaine.

While the size of the cocaine-using population has grown substantially in the past halfdozen years compared with that of the marijuana-using population, the two are still not in the same league. Moreover, since marijuana tends to be used more frequently by the typical regular user than is true of cocaine, the total number of episodes of marijuana use is many times, perhaps ten times, the total number of episodes of cocaine use. It is possible that the total number of times that marijuana is used approaches, and may even exceed, the total for all other illicit drugs combined. Any discussion of the use of illegal drugs in America must begin with marijuana.