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THE MARIJUANA GATEWAY EFFECT
As the controversy surrounding the legalization of medicinal marijuana has intensified in recent years, voices on both sides of the issue cite theories, statistics, and studies, many of which range from simply misleading to flat-out false. Unfortunately, it is often very difficult to distinguish fact from fiction, due to the complexity of the problem of marijuana use and the vast amount of information available regarding this problem. Because of the nebulous nature of the world of marijuana-related information, special interest groups are often able to make fallacious claims regarding the science of marijuana.
As the amount of information on marijuana is overwhelming, this paper will focus on one aspect of the debate: the validity of the marijuana gateway effect. Is marijuana use a factor in progression to illicit drugs? If it is a factor, to what degree does marijuana use alone contribute to the progression from soft to hard drugs? And, perhaps most importantly, should the government continue to promote the marijuana gateway theory as fact?
THE MARIJUANA PLANT
Marijuana, commonly used as a recreational drug, comes from the female plants of the genus Cannabis Sativa. 2 Marijuana is aptly named “weed”, as it is in fact a plant that can grow with relatively little human assistance in most areas with a temperate or tropical climate, ranging from its original home in the Caucasus regions to North America. 1 It is a hardy plant that can adapt to many soil and climate conditions and reach maturity quickly. 1 The active ingredient in marijuana is delta-9-tetrahydrocannabinol, a mildly hallucinogenic compound that is typically found in concentrations ranging from .5 percent to 14 percent. 3 Marijuana has been used medicinally to alleviate symptoms involved with glaucoma, migraines, cancer, and herpes. 4
THE PREVALENCE OF MARIJUANA
According to Gallup Polls, the prevalence of marijuana use in the United States is steadily on the rise. In 1969, only 3.94 percent of the population admitted to using marijuana. Just four years later, the percentage of affirmative responses had almost tripled to 11.82 percent. By 1999, nearly one third of the population (33.61 percent) admitted to having smoked marijuana. 6
THE MARIJUANA GATEWAY EFFECT
The gateway model was developed to explain a number of statistical sets that showed a correlation between the use of marijuana, alcohol, and tobacco, and the use of so-called “harder” drugs (heroin, cocaine, LSD, etc.) in adolescents (Morral et al., 2002). The marijuana gateway effect refers specifically to marijuana’s contribution to this general gateway effect. These statistics generally fit into three different subsets, all of which are used to support the marijuana gateway effect. The first simply demonstrate that users of marijuana will be at a higher risk to experiment with hard drugs than non-users. This is supported by results from a number of studies in a number of different countries and cultures (Adler & Kandel, 1981; Stenbacka, Allebeck & Romelsjo, 1993; Beenstock & Rahav, 2002). The second statistical set is related to the order in which different classes of drugs are first used. Drug abuse rarely begins with hard drugs and regresses to marijuana. A longitudinal study of 1265 New Zealand adolescents between 15 and 21 years of age revealed only three cases (.237 percent) in which hard drug use was initiated before marijuana use (Fergusson & Horwood, 2000). The third factor used to support the marijuana gateway effect is the strong correlation between the frequency of marijuana use and the rate of hard drug initiation (Morral et al., 2002). A proportional hazards model implied that those using marijuana more than 50 times per year were 140 times more likely to progress to hard drugs than those test subjects using no cannabis (Fergusson & Horwood, 2000). This correlation between number of marijuana usage and progression to harder drugs has been labeled the dose-response effect (Morral et al., 2002). These three relationships between marijuana and hard drug use would suggest that the marijuana gateway effect has a solid foundation in science.
THE COMMON LIABILITY THEORY
Though results from a number of studies could support the marijuana gateway theory, they do not conclusively prove that the correlation between marijuana use and hard drug use is causal, and ignore the possibility that this relationship is the effect of some outside factor. There are several theories that can also explain the very same data in a very different way. One such theory is the common liability theory (Morral et al., 2002).
Rooted in the biopsychosocial perspective, the common liability theory suggests that marijuana use itself is not the cause for progression to hard drugs, but rather propensity for drug use, which is the result of a combination of genetic, familial, and environmental factors. (Agrawal et al., May 2004) Furthermore, the common liability theory recognizes marijuana use as a possible identifier of an individual at risk for progression to illicit drug use. To this end, the common liability theory could be considered as a method for identifying risk factors that lead to illicit drug use - environment, culture, marijuana, alcohol or tobacco use all being risk factors that might cause or identify potential illicit drug use (Agrawal et al., May 2004).
AGRAWAL ET AL., OCTOBER 2004
The common liability theory was tested against the gateway theory using both monozygotic and dizygotic twins (Agrawal et al., October 2004). The experiment was designed to assess the extent to which early cannabis use in twin 1 predicted the subsequent use of other illicit drugs in twin 2 after controlling for twin 2's early cannabis use. The dyzgotic twins have no greater genetic similarity than any other pair of siblings, while monozygotic twins, having developed from the same fertilized egg, have identical genetic information. As anticipated by the common liability theory, illicit drug use was a more accurate predictor for future illicit drug use by a sibling in monozygotic twins than in dizygotic twins. Specifically, the odds ratios, or chance of illicit drug progression in siblings, were 1.0 to 4.5 times higher for monozygotic twins than for dizygotic twins. This suggests the possibility that genetics play an important role in the progression from marijuana use to illicit drug use (Agrawal et al., October 2004).
THE ECONOMIC APPROACH
Another interesting theory that illustrates the complexity of the interplay between marijuana and illicit drugs revolves around the application of economic principles. The economic approach equates the marijuana gateway effect with an economic relationship between consumer demand for marijuana and consumer demand for illicit drugs (Kenkel et al., 2001). Although the potential supply of drugs is typically dependant on the drug-seeking behavior of the individual, external forces can cause changes in supply and demand. For example, should the government increase its efforts to seize marijuana, the supply of marijuana will decrease, consequently causing a jump in marijuana prices. However, illicit drug supplies were not decreased, so their prices remain static. Drug users might turn to the less expensive and more readily available illicit drugs as an alternative to marijuana. The gateway effect theory, however, would predict that a lessened supply of marijuana should lead to a lower amount of marijuana use, and thus, a lower amount of illicit drug use. Due to their pragmatic logic, economic systems might be the focus of drug-related studies in the future, as researchers seek to test the gateway effect theory in new ways. (Kenkel et al., 2002)
PROBLEMS WITH MARIJUANA GATEWAY THEORY
The marijuana gateway theory suggests that only marijuana use contributes to the subsequent use of other drugs. The research needed to confirm this theory is, unfortunately, an impossibility. Unlike research on animals in a laboratory, human environmental influences cannot be controlled. Therefore any attempt to prove that marijuana use alone will result in a progression to illicit drugs, is doomed from the start. Subjects for this study lacking any previous environmental, social, or cultural influences will never be found. Ultimately, the biopsychosocial perspective limits the viability of the marijuana gateway theory as an accurate approach to understanding marijuana’s effects on illicit drug use.
GOVERNMENTAL SUPPORT OF GATEWAY THEORY
Governmental use of the marijuana gateway theory in policy making could have unintended and unwanted effects. Since the marijuana gateway theory predicts that increased marijuana use will result in increased illicit drug use, the contra-positive would also be assumed to be true. Using this theory as the basis for policy making might unintentionally increase illicit drug use as described in the section regarding economic applications (Kenkel et al., 2002). Furthermore, recent research proposes that the most serious of drug users do not necessarily follow the progression suggested by the marijuana gateway theory (Mackesy-Amiti et al., 1997). Therefore, those most at risk to become seriously addicted to illicit drugs will not be affected by anti-drug campaigns that focus on prevention of drug, alcohol, and tobacco use. As a result of these reasons, the government would be well advised not to base its policies entirely on the marijuana gateway effect theory (Mackesy-Amiti et al., 1997).
Although all studies examined indicate that early use of marijuana elevates the risk of progression to illicit drugs, the exact nature of this association is still unknown. Of the five studies investigated, none concluded the previously mentioned association as proof of the validity of the marijuana gateway effect. However, the lack of proof does not invalidate the marijuana gateway effect. As a result, it is necessary for further research to be done on this topic.
Until a time comes when available research indicates conclusively the legitimacy of any one theory - be it marijuana gateway effect, common liability theory, or another – the government should not actively promote one theory over another. Rather the government should seek to educate people on all available theories, which will generally result in a greater societal understanding of the problems involving marijuana use. Governmental advocation of incomplete scientific findings is a dangerous thing, which can only be combated by impartial third parties examining the science without bias or prejudice.
It should be noted that marijuana, though classified as a soft drug, can cause a number of serious physical and psychological illnesses (Rafael et al., 2002). The dangers of smoking marijuana have increased with time, as the THC content in cannabis plants continue to escalate. Simply because Marinol, a THC pill taken by cancer and other terminally ill patients, is legal and is prescribed by doctors, does not make smoking marijuana a healthy or safe activity. 5
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COVER PICTURE: Retrieved on September 20, 2005 from the National Institute on Drug Abuse: http://www.teens.drugabuse.gov/facts/facts_mj1.asp
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