“Critics claim that marijuana is a ‘gateway drug.’ How do you respond to this charge?”. National Organization for the Reform of Marijuana Laws. Retrieved 2.19.08 – “There is no conclusive evidence that the effects of marijuana are causally linked to the subsequent use of other illicit drugs. Preliminary animal studies alleging that marijuana “primed” the brain for other drug-taking behavior have not been replicated, nor are they supported by epidemiological human data. Statistically, for every 104 Americans who have tried marijuana, there is only one regular user of cocaine, and less than one user of heroin. Marijuana is clearly a ‘terminus’ rather than a gateway for the overwhelming majority of marijuana smokers.”
From Wikipedia (needs reformatting)
In 1997, the Connecticut Law Revision Commission examined states that had decriminalized marijuana and found decriminalizing small amounts of marijuana has no effect on subsequent use of alcohol or “harder” illicit drugs. The study recommended Connecticut reduce marijuana possession of one ounce or less for adults age 21 and over to a civil fine.
In 1999, a study by the Division of Neuroscience and Behavioral Health at the Institute of Medicine entitled “Marijuana and Medicine: Assessing the Science Base,” found no evidence of a link between marijuana use and the subsequent abuse of other illicit drugs on the basis of its particular physiological effect.
In December 2002, a study by RAND regarding if marijuana use results in the subsequent use of cocaine and heroin was published in the British Journal of Addiction. The researchers created a mathematical model simulating adolescent drug use. National rates of marijuana and hard drug use in the model matched survey data collected from representative samples of youths from across the United States; the model produced patterns of drug use and abuse. The study stated:
The people who are predisposed to use drugs and have the opportunity to use drugs are more likely than others to use both marijuana and harder drugs … Marijuana typically comes first because it is more available. Once we incorporated these facts into our mathematical model of adolescent drug use, we could explain all of the drug use associations that have been cited as evidence of marijuana’s gateway effect … We’ve shown that the marijuana gateway effect is not the best explanation for the link between marijuana use and the use of harder drugs.
In 2004, a study by Craig Reinarman, Peter D. A. Cohen, and Hendrien L. Kaal entitled “The Limited Relevance of Drug Policy: Cannabis in Amsterdam and in San Francisco,” was published in the American Journal of Public Health. The study found no evidence that the decriminalization of marijuana leads to subsequent abuse of other illicit drugs. The study also found the mean age at onset of marijuana use and the mean age of marijuana users are both higher in Amsterdam than in San Francisco.
In 2006, the Karolinska Institute in Sweden used twelve rats to examine how adolescent use of marijuana affects subsequent abuse of other illicit drugs. The study gave six of the twelve “teenage” rats a small dose of THC, reportedly equivalent to one joint smoked by a human, every three days. The rats were allowed to administer heroin by pushing a lever and the study found the rats given THC took larger doses of heroin. The institute examined the brain cells in the rats and found THC alters the opioid system that is associated with positive emotions, which lessens the effects of opiates on rat’s brain and thus causes them to use more heroin. Paul Armentano, policy analyst for NORML, claimed because the rats were given THC at the young age of 28 days, it is impossible to extrapolate the results of this study to humans.
In December 2006, a 12 year gateway drug hypothesis study on 214 boys from ages 10-12 by the American Psychiatric Association was published in the American Journal of Psychiatry. The study concluded adolescents who used marijuana prior to using other drugs, including alcohol and tobacco, were no more likely to develop a substance abuse disorder than subjects in the study who did not use marijuana prior to using other drugs.