Yep, it's long, but worth a look...
'Cannabis is a Gateway Drug and therefore should not be legalized' is a common argument used by anti-cannabis proponents. The argument is usually put forward by people who believe that if you start smoking pot, you are more likely to end up using harder drugs such as LSD, Cocaine, Crack, Heroin and other chemical narcotics. Some more extreme anti-cannabis campaigners believe that the evil weed always leads to harder drug use and other crimes such as assaults burglary and even murder.
When the issue is looked at properly, the inevitable path to 'drug addicted destruction from smoking pot' argument starts to fall apart pretty quickly . So it's time look at some more (referenced) facts.
Before we get into the science, here is a quick overview of how the 'Gateway' myth started. Interestingly, this article shows that in the early days of Marijuana prohibition, the fear was that Heroin addicts would move on to Cannabis, not the other way around:
How Did The Marijuana Gateway Myth Get Started?
The reason marijuana had to be outlawed, he said (Harry Ainslinger in 1937), was because it caused insanity, criminality, and death. One example he gave was of two young lovers who became so crazed after smoking a joint that they eloped and got married. Marijuana causes people to become so crazy that they get married. The other reasons he gave were no more sensible. The hemp industry representatives who testified were uniformly surprised and mystified to hear that a dangerous drug could be made from this widespread and common crop. The American Medical Association testified that they knew of no evidence that marijuana was a dangerous drug...
...In 1951, the story changed. Harry Anslinger was testifying for the Boggs Act about why he needed more money and men to enforce the marijuana laws. Just before he testified, the head of the Federal addiction research program testified that they knew for certain that all of the reasons that had been given for outlawing marijuana in 1937 were entirely bogus. They knew for certain that marijuana did not cause insanity, criminality and death. Anslinger was left with no reason for tougher laws so he made up -- on the spot, with not a shred of evidence -- the assertion that marijuana is the certain stepping stone to heroin addiction. He directly contradicted his own testimony from 1937. It has been the basis of US marijuana policy ever since.
Time for some science.
An article written by John P. Morgan, M.D. (d) and Lynn Zimmer, Ph.D (d), entitled 'The Myth of Marijuana's Gateway Effect' states in part:
The primary basis for this "gateway hypothesis" is a recent report by the center on Addiction and Substance Abuse (CASA), claiming that marijuana users are 85 times more likely than non-marijuana users to try cocaine. This figure, using data from NIDA's 1991 National Household Survey on Drug Abuse, is close to being meaningless. It was calculated by dividing the proportion of marijuana users who have ever used cocaine (17%) by the proportion of cocaine users who have never used marijuana (.2%). The high risk-factor obtained is a product not of the fact that so many marijuana users use cocaine but that so many cocaine users used marijuana previously.
It is hardly a revelation that people who use one of the least popular drugs are likely to use the more popular ones -- not only marijuana, but also alcohol and tobacco cigarettes. The obvious statistic not publicized by CASA is that most marijuana users -- 83 percent -- never use cocaine. Indeed, for the nearly 70 million Americans who have tried marijuana, it is clearly a "terminus" rather than a "gateway" drug.
The Australian National Council on Drugs (ANCD), the principal advisory body to the Australian Federal Government on drug policy, states in its document 'Cannabis: Answers to Your Questions' (PDF file link):
What is the Current Evidence For Cannabis as a Gateway Drug?
Cannabis use, particularly regular use at a young age, increases the risk of other drug use. The link between cannabis use and the use of other illicit drugs is usually due to personal traits that make it more likely for the person to take part in risky behaviour.
Most people who use illegal drugs, like heroin or amphetamines, first used drugs like alcohol, tobacco or cannabis. These substances, but most usually cannabis, are seen as a “gateway” to the use of other drugs. The vast majority of people who do use cigarettes, alcohol or cannabis never use other illicit drugs. For example, while the majority of heroin users have used cannabis, only around 4% of cannabis users have used heroin.
The risk of using other drugs is greater for cannabis users who start regularly using at a young age and those who become dependent.The link between cannabis use and the use of other illicit drugs is usually due to personal traits(possibly even genetic) that make it more likely for the person to take part in risky behaviour. Mixing with people who use illicit drugs also means there are more opportunities to experiment.
Approximately 18 months ago, The Pittsburgh Post-Gazette reported on a study led by Ralph E. Tarter, a professor at the University of Pittsburgh's School of Pharmacy. A quote from the article reads:
"It runs counter to about six decades of current drug policy in the country, where we believe that if we can't stop kids from using marijuana, then they're going to go on and become addicts to hard drugs."
The full text of this research is available on the Psychiatry Online website here.
For those who don't want to read the full text, here are the results and conclusions of the study as stated in the Abstract:
RESULTS: Twenty-eight (22.4%)of the participants who used marijuana did not exhibit the gateway sequence, thereby demonstrating that this pattern is not invariant in drug-using youths. Among youths who did exhibit the gateway pattern, only delinquency was more strongly related to marijuana use than licit drug use. Specific risk factors associated with transition from licit to illicit drugs were not revealed. The alternative sequence had the same accuracy for predicting substance use disorder as the gateway sequence.
CONCLUSIONS: Proneness to deviancy and drug availability in the neighborhood promote marijuana use. These findings support the common liability model of substance use behavior and substance use disorder.
In yet another study (available here in HTML, or here as a Microsoft Word Document), the findings were that although cannabis may have a gateway effect on a small number of (and I quote) "troubled youths", in the majority, there is no evidence to support cannabis as a drug that leads to narcotic use. The study states that a number of different factors contribute to further hard drug use, rather than cannabis being a cause.
Now, on to the DSM-IV.
This is the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition. The main reference used around the world by psychiatrists, clinicians and researchers as well as insurance companies, pharmaceutical companies and policy makers.
In the section titled 'NCP Hallucinogen Phencyclidine and Cannabis Related Disorders' it gives the following information (Etilology:-The cause of a disease, the philosophical study of causation):
Individuals who abuse substances fail to complete tasks of separation-individuation, resulting in underdeveloped egos. The person is thought to have a highly dependent nature, with characteristics of poor impulse control, low frustration tolerance, and low self-esteem. The superego is weak, resulting in absence of guilt feelings for behavior.
Certain personality traits may play an important part in the development and maintenance of dependence. Characteristics that have been identified include impulsivity, negative self-concept, weak ego, low social conformity, neuroticism, and introversion. Substance abuse has also been associated with antisocial personality and depressive response styles.
A genetic link is thought to be involved in the development of substance abuse disorders. Although statistics are currently inconclusive, hereditary factors are generally accepted to be a factor in the abuse of substances. Research is currently being done into the role biochemical factors play in the problems of substance abuse.
A predisposition to substance use disorders is found in the dysfunctional family system. Often one parent is absent or is an overpowering tyrant, and/or another parent is weak and ineffectual. Substance abuse may be evident as the primary method of relieving stress. The child has negative role models and learns to respond to stressful situations in like manner. However, parents may be average, normal individuals with children who succumb to overwhelming peer pressure and become involved with drugs.
In the family the effects of modeling, imitation, and identification on behavior can be observed from early childhood onward. Peer influence may exert a great deal of influence also. Cultural factors may help to establish patterns of substance use by attitudes of acceptance of such use as a part of daily or recreational life.
So, we can argue that cannabis can lead to further drug use. However, it is in no way a primary cause of going on to harder drugs. In fact, it is probably easier to argue that cannabis is a terminus drug, meaning that the majority of people who use cannabis will never go on to use harder drugs.
On a final note, let's look at what has happened in The Netherlands since cannabis was decriminalized in 1976. One would expect that if the mainstream perceptions of the 'Gateway' theory were correct, then this country would be full of Heroin addicted kids and adults. From what I've read so far, this is far from the case.
First, in a study I have mentioned previously that is reported in the UCSC in 2004:
The study found no evidence that lawfully regulated cannabis provides a “gateway” to other illicit drug use. In fact, marijuana users in San Francisco were far more likely to have used other illicit drugs--cocaine, crack, amphetamines, ecstasy, and opiates--than users in Amsterdam, said Reinarman.
“The results of this study shift the burden of proof now to those who would arrest hundreds of thousands of Americans each year on the grounds that it deters use,” said Reinarman.
More on this study is available on the 'News-Medical' website here.
Another study, available here in full, found the following:
In Amsterdam, the access to cannabis type drugs developed from highly suppressed to almost universal and hassle free in the period between 1965 and 1980. We tested the theory that cannabis use will - almost automatically - result in (heavy) use of other drugs. Indeed, we found among almost 9,000 respondents out of 2 large household surveys in 1990 and 1994, that in Amsterdam cannabis use is an almost necessary condition for developing other drug use. However, most cannabis users in Amsterdam (75%) do not report other drug use. Also the 'never cannabis users' in Amsterdam do not consume other illicit drugs. Curiosity inasmuch as it develops in cannabis users to use other drugs is confined to cocaine and ecstasy, while heroin is almost excluded.
In order to test the 'stepping stone hypothesis' we formulated a testable series of such hypotheses, varying the terms but keeping the criterion stable. We arbitrarily stated that any of our stepping stone hypotheses would be confirmed if we could find 75% of the cannabis users to behave according to the hypothesis. None of the stepping stone hypotheses could be confirmed although data that approached confirmation could be found for a minority of users with the highest levels of cannabis involvement. Some statistical / epidemiological evidence for a stepping stone phenomenon that associates cannabis use to some type of use of other drugs is available for a small minority of cannabis users only.
Apparently, in Amsterdam where use of illicit drugs is made possible due to of hassle free (illicit) availability of that type of drug, the use of cannabis satisfies almost all curiosity. Small numbers of experienced cannabis users try other illicit substances, mostly cocaine and ecstasy. This is true for cannabis users who never experienced active law enforcement against individual drug use (the 'young' age cohort born in 1985 or later) as well as for cannabis users who were raised during the then existing regime of active law enforcement against cannabis and other individual drug use (the 'old' age cohort born before 1958). We confirmed that, if it occurs, other drug use always succeeds use of cannabis. We did not try to explain why this is so, nor why the large majority of cannabis users do not develop curiosity to use other drugs.
Levels of experience with other drugs than cannabis are very similar between different cannabis users in age cohorts raised during different regimes of law enforcement in relation to drugs.
Will Decriminalization Lead To Rampant Marijuana Use?
For those who wish to argue that cannabis decriminalization will lead to a marked increase in the use of the drug, you should read this report.
Conflicting predictions have been made to the influence of decriminalisation on cannabis use. Prohibitionists forecast that decriminalisation will lead to an increase in consumption of cannabis, while their opponents hypothesise that cannabis use will decline after decriminalisation.
Most probably cannabis use among youth in the Netherlands so far evolved in two waves, with a first peak around 1970, a low during the late 1970s and early 1980s, and a second peak in the mid 1990s.
It is striking that the trend in cannabis use among youth in the Netherlands rather parallels the four stages in the availability of cannabis identified above. The number of adolescent cannabis users peaked when the cannabis was distributed through an underground market (late 1960s and early 1970s). Then the number decreased as house dealers were superseding the underground market (1970s), and went up again after coffee shops took over the sale of cannabis (1980s), and stabilised or slightly decreased by the end of the 1990s when the number of coffee shops was reduced.
However, cannabis use also developed in waves in other European countries. Apparently, general national trends in cannabis use are relatively independent of cannabis policy. To date, cannabis use in the Netherlands takes a middle position within the European Union. Apparently most cannabis use is experimental and recreational. The vast majority quits using cannabis after some time. Only a very small proportion of current cannabis users is in treatment. From international comparison, it is concluded that trends in cannabis use in the Netherlands are rather similar to those in other European countries, and Dutch figures on cannabis use are not out of line with those from countries that did not decriminalise cannabis. Consequently, it appears unlikely that decriminalisation of cannabis will cause an increase in cannabis use.