MARIJUANA IS A GATEWAY DRUG?
Even if marijuana itself causes minimal harm, it is a dangerous substance because it leads to the use of “harder drugs” like heroin, LSD, and cocaine.
“Marijuana use is on the rise. . . . These findings are especially alarming since the use of marijuana–the most widely used drug often leads to the use of other, more dangerous drugs.”
“Children who have used marijuana are 85 times likelier to use cocaine than children who have not used marijuana.”
“It appears that the biochemical changes induced by marijuana in the brain result in a drug-seeking, drug-taking behavior, which in any instances will lead the user to experiment with other pleasurable substances.”
“Since marijuana use, harmful as it is in its own right, is often a prelude to the use of other drugs . . . [it is] doubly disastrous.”
“Although marijuana is not as addictive or toxic as cocaine, smoking marijuana–or seeing others smoke marijuana–might make some individuals more disposed to use other drugs.”
MARIJUANA DOES NOT CAUSE PEOPLE TO USE HARD DRUGS.
What the gateway theory presents as a causal explanation is a statistical association between common and uncommon drugs, an association that changes over time as different drugs increase and decrease in prevalence. Marijuana is the most popular illegal drug in the United States today. Therefore, people who have used less popular drugs, such as heroin, cocaine, and LSD, are likely to have also used marijuana. Most marijuana users never use any other illegal drug.
Indeed, for the large majority of people, marijuana is *terminus *rather than a *gateway* drug. PROPONENTS of the gateway theory, formerly known as the “stepping-stone hypothesis,” argue that even if marijuana itself is not very dangerous, marijuana leads people to use other more dangerous drugs. In the 1950s, marijuana was said to be a gateway to heroin, and in the 1960s, a gateway to LSD. Today, marijuana is discussed primarily as a gateway to cocaine.
People who use cocaine, a relatively unpopular drug, are likely to have used the more popular drug, marijuana. Marijuana users are also more likely than nonusers to have had previous experience with legal drugs, such as alcohol, tobacco, and caffeine. Alcohol, tobacco, and caffeine do not cause people to use marijuana. Marijuana does not cause people to use heroin, LSD, or cocaine.
The relationship between marijuana and other drugs varies across societies. Within the United States, the relationship varies across age groups and substances, and from one social group to another. Over time, as any particular drug increases or decreases in popularity, its relationship to marijuana changes. While marijuana use was increasing in the 1960s and 1970s, heroin use was declining. During the past twenty years, as marijuana use rates fluctuated, rates for LSD remained constant. Cocaine became popular in the early 1980s as marijuana use was declining later, both marijuana and cocaine use declined. Recently, marijuana use has increased while the decline in cocaine use has continued.
Figure 4-1 illustrates the changing relationship between marijuana use and cocaine use over time. At the height of cocaine’s popularity in 1986, 33 percent of high school seniors who had used marijuana had also tire cocaine. By 1995, only 14 percent of marijuana users had tried cocaine.
Even when marijuana users try cocaine, they do not necessarily become regular users. In fact, very few do. As shown in figure 4-2, of the seventy-two million Americans who have used marijuana, about twenty million have tried cocaine. Of this twenty million, about 30 percent used cocaine only once or twice. Only 17 percent used cocaine more than one hundred times. In other words, for every one hundred people who have used marijuana, *only one *is a current regular user of cocaine.
The probability of trying cocaine is not distributed equally across the population of marijuana users. Teens who use marijuana occasionally, and use no illicit drugs other than marijuana, are unlikely to ever try cocaine. Indeed, most teens who try marijuana never even become regular users of marijuana. In 1994, among twelve to seventeen year-olds who had tried marijuana, 60 percent had used it fewer than twelve times and about 40 percent had tried it only once or twice.
Studies show that most teens who try cocaine have had many previous drug experiences. Most began using alcohol and marijuana at an earlier age than their peers, and most continue to use both alcohol and marijuana frequently. Most also tried numerous other illicit drugs before trying cocaine. One study, looking at adults who had been marijuana users in high school, found that over 80 percent of those who eventually tried cocaine were already multiple-drug users. They regularly used alcohol, tobacco, and marijuana, and had also tried stimulants, sedatives, and psychedelics.
Few adolescents become early multiple-drug users, and those who do differ from their peers in a number of ways. They are more likely to be poor, more likely to live in neighborhoods where illicit drug use is prevalent, less likely to come from stable homes, less likely to be successful at school, and more likely to have psychological problems. Most multiple-drug users engage in a variety of deviant and delinquent activities prior to using legal or illegal drugs. In other words, within the general population of adolescent marijuana users, there is a deviant minority who become multiple -drug users.
A report by the Center on Addiction and Substance Abuse (CASA) says that youthful marijuana users are eighty-five times more likely than nonusers to use cocaine. CASA’s calculation is based on marijuana and cocaine prevalence data from 1991. To obtain the eighty-five times “risk factor,” CASA divided the proportion of marijuana users who had ever tried cocaine (17 percent) by the proportion of cocaine users who had never tried marijuana (0.2 percent). The “risk factor” is large not because so many marijuana users experiment with cocaine, but because very few people try cocaine without trying marijuana first.
Recent animal studies showing that THC increases the availability of dopamine in the brain’s “pleasure-reward substrate” are used to claim that marijuana”primes” the brain for heroin and cocaine, drugs which also affect dopamine’s availability in this system. Other researchers have failed to find dopamine effect from THC, More importantly, there are no studies showing that “priming” animals with injections of THC increases their willingness to self-administer heroin or cocaine. After injections of THC, animals will not even self-administer THC. In short, pharmacological explanations for a gateway effect from marijuana have no foundation.
In the end, the gateway theory is not a theory at all. It is a description of the typical sequence in which multiple-drug users initiate the use of high-prevalence and low-prevalence drugs. A similar statistical relationship exists between other kinds of common and uncommon related activities. For example, most people who ride a motorcycle (a fairly rare activity) have ridden a bicycle (a fairly common activity). Indeed, the prevalence of motorcycle riding among people who have never ridden a bicycle is probably extremely low. However, bicycle riding does not cause motorcycle riding, and increases in the former will not lead automatically to increases in the latter. Nor will increases in marijuana use lead automatically to increases in the use of cocaine or other drugs.