Myth: The use of marijuana causes users to go on to harder drugs such as heroin and cocaine. It is often cited by police and anti marijuana groups.
The Truth: First of all this is not a theory of any kind. It would even be hard to call it a hypothesis because it has no scientific backing. Let me elaborate. To prove causality it is necessary to fulfil three criteria, which were originally proposed by 18th century philosopher David Hume. These criteria are: Association, Temporal Antecedence and Isolation. Association means the cause and effect must occur together, temporal antecedence means the effect must follow the cause and isolation means all other causes must be ruled out. The simplest way to prove causality is an experiment designed such that: the cause leads to the effect and absence of the cause will cause no effect (or a different one). Since an experiment where people are randomly exposed to marijuana to see who goes on to snort coke and shoot heroin is considered unethical there is no way to absolutely prove the theory.
Correlation studies examine users of crack or heroin and ask them which drugs they used previously. These studies satisfy association and temporal antecedence but fail to prove isolation. For example a study could show that the crime rate in a city grows as the number of churches increases. You could draw the conclusion that churches cause crime. Further evidence could show that the churches were built first adding more support for the idea. This still does not prove that churches cause crime. A more realistic solution is that as cities grow larger both the number of churches and crime rates increase. The gateway theory is equally ridiculous as the church-crime theory.
In 2006, 25 million Americans age 12 and older had abused marijuana and 560,000 had abused heroin at least once in the year prior to being surveyed [Source: Nationa Survey on Drug Use and Health]. That’s 14.5% of Americans using pot and 0.2% using heroin. If we look at the same survey but for number who have tried each drug in their lifetime the numbers are: 45.4% marijuana and 1.5% heroin. As you can see there are many more people using marijuana then heroin. No surprise there. Also heroin use rate has remained roughly the same since the 60s while marijuana use has increased significantly. Look at the following graphs: % of Americans who have tried marijuana (top) and % of Americans who have tried heroin (bottom)
As you can see there is no relationship between marijuana use rate and heroin use rates. Marijuana use has gone up while heroin use has stayed relatively the same. While it may be true that heroin and other hard drug users started with marijuana their progression onto harder drugs had nothing to do with the marijuana itself. The gateway theory is total bullshit. It was created by anti-marijuana groups once the public realized that marijuana is not as harmful as they said was. They needed something that would put the fear into parents and naive users. Don’t be fooled friends gateway theory is a myth.
- A Treatise of Human Nature, David Hume, 1740.
- Tarter, Ralph E.; Michael Vanyukov, Levent Kirisci, Maureen Reynolds and Duncan B. Clark, M.D. (December 2006). “Predictors of Marijuana Use in Adolescents Before and After Licit Drug Use: Examination of the Gateway Hypothesis” (abstract). American Journal of Psychiatry 163