There is a theory that suggests that marijuana is a 'gateway' drug that leads to a person using other drugs. A dangerous misperception surrounding this is that these people implicitly assume that marijuana is less dangerous than other drugs. In fact, any drug is equally dangerous to a drug addict and will lead to similar consequences.

The original research into this theory claimed that marijuana usage led to heroin use. It is always difficult to show a cause and effect relationship between two behaviours, and this claim was based on the observation that most heroin users had also tried marijuana previously.

This is not a very scientific argument, however, as all that this demonstrates is that many heroin users have also tried marijuana. There could be a great many other reasons that a person is using heroin and trying marijuana could be related to some other factor.

The term "drug of choice" is in common parlance with people in recovery. It is understood to mean that if the addict has a choice between a variety of substances this particular drug would be the one they would like to use most. Anecdotal evidence suggests that addicts will try a few substances before settling on the one they enjoy most. It is quite possible that the addict was looking for the effects that heroin provides and tried marijuana only to discard it because it did not provide the "right" effect.

The Disease Model of addiction suggests that a substance abuse disorder is a primary condition that exists in and of itself. Research has consistently demonstrated that the only predictor variable regarding addiction is the availability of substances. That is to say that age, race, sexual identity, socioeconomic status, religion, or any other factor is as important in determining who becomes an addict as the availability of drugs. It stands to reason: If there are lots of easily accessible drugs around then it is easier to experiment with them and so you are more likely to develop addiction.

Marijuana is generally more easily available than heroin and we would expect people to first experiment with the easily obtainable drug. The misconception that marijuana is safer than heroin makes it psychologically easier for people to decide to try it. Additionally heroin is often associated with needles and overdoses. These sort of associations make heroine less likely to be the first drug somebody tries.

In this way marijuana could be seen as a softer entry point into behaviour associated with drug use. But it would not mean that smoking marijuana leads to heroin abuse. Rather it would mean that the user is exposed to the lifestyle of an addict - breaking the law, seeking an illicit substance, and secretly using it. This might remove some of the psychological hurdles that prevent a person from trying heroin.

The British Home Office has published a report ("The Road to Ruin?") that concluded that cannabis does not lead to people trying other drugs. It suggested that people who are likely to be addicts will try substances based on their personal predisposition rather than on their previous experience with marijuana.

The rather weakly supported idea that "marijuana leads to using other drugs" needs to be seen in the socio-political context in which it was popular. This assertion was based on research conducted in America in the 1980's. At this time the government was conducting its war on drugs with varying degrees of success. Research such as this would have been used as a public health intervention to attempt to alter the public perception that "marijuana is safe".

Cannabis itself is definitely addictive. Chronic users are able to smoke more ("tolerance") and display withdrawal effects if the drug is taken away from them. Cannabis addiction leads to problems arising from the impaired cognitive capacity while intoxicated, as well as the general sense of lethargy and paranoia that chronic use engenders. There are specialist drug treatment programs to assist people in coming off marijuana. If this substance were "safe" and "non-addictive" there would be no need for such programs.

In my opinion marijuana is associated with enough inherent risks to discourage its usage without having to make weak links to heroin use. There is an association between marijuana and schizophrenia. Marijuana is more carcinogenic than tobacco products. Chronic marijuana use is associated with paranoia, lethargy, and physiological effects. Claiming that it is a "gateway" drug diminishes the perception of danger that should accompany it.