Gateway drug
Encyclopedia
The gateway drug theory is the hypothesis that the use of less deleterious drugs may lead to a future risk of using more dangerous hard drugs and/or crime. It is often attributed to the use of several drugs, including tobacco
, alcohol
, and cannabis
.
While some research shows that many hard drug users used cannabis or alcohol before moving on to the harder substances, other research shows that some serious drug abusers have used other drugs before using cannabis or alcohol.
The former is particularly evident in individual drug-abuse histories which tend to show that "hard drug" users do progress from one drug to another.
can possibly predict a significant higher risk for the subsequent use of other "harder" illicit drugs, while other studies show that it cannot. Two recent studies are from University of Pittsburgh
's School of Pharmacy
, and from Dr. Michael Lynskey.
at age 14–15 years. This cohort was interviewed on eight occasions until the age of 24–25 years. At age 24 years, 12% of the sample had used amphetamines in the past year, with 1%–2% using at least weekly. Young adult amphetamine use was predicted strongly by adolescent drug use and was associated robustly with other drug use and dependence in young adulthood. Associations were stronger for more frequent users. Among young adults who had not been using amphetamines at age 20 years, the strongest predictor of use at age 24 years was the use of other drugs, particularly cannabis, at 20 years. Those who were smoking cannabis at the age of 15 were as much as 15 times more likely to be using amphetamines in their early 20s.
attempted to dissect the contribution of genetic, shared environmental and unique environmental influences on the development of dependence on other drugs in those who had used cannabis. The study found that while cannabis was strongly predictive of use of other drugs in the future, the main contributors to this effect were the shared environmental and genetic risk for all substances. However, there was "persisting evidence for some causal influences" of cannabis in the development of other drug dependencies, indicating that the gateway theory could be operative, although not the main cause of the association.
used twelve rats to examine how adolescent use of cannabis affects subsequent abuse of other illicit drugs. The study gave six of the twelve "teenage" (28–49 days old, or 6.6–10.4 in human years) rats a small dose of THC
, reportedly equivalent to one cannabis joint smoked by a human, every three days. The rats were allowed to self-administer heroin by pushing a lever and the study found the rats given THC took larger doses of heroin (but no such effect was found for amphetamines).
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 opiate
s 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, is impossible to extrapolate the results of this study to humans. Also, the previously cannabis-exposed adult rats, despite being desensitized to heroin, were no more likely to get addicted (as measured by likelihood of self-administration) than the controls. In addition, not all animal studies agree with the results found in this study (see below).
entitled "Marijuana and Medicine: Assessing the Science Base," found no evidence of a link between cannabis use and the subsequent abuse of other illicit drugs on the basis of its particular physiological effect.
regarding if cannabis use results in the subsequent use of cocaine
and heroin was published in the British Journal of Addiction, a peer-reviewed scientific publication. The researchers created a mathematical model simulating adolescent drug use. National rates of cannabis 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. Andrew Morral, associate director of RAND's Public Safety and Justice unit and lead author of the study stated:
One reason the risk factor for abusing drugs in cannabis users is higher is because few people try hard drugs prior to trying cannabis, not because cannabis users increasingly try hard drugs such as amphetamines. For example, cannabis is typically available at a significantly earlier age than other illicit drugs. Further research has shown that people with a disposition to resort to cannabis use are more likely to live longer and healthier lives than users of other "social drugs" such as alcohol.
was published in the American Journal of Psychiatry
. The study concluded adolescents who used cannabis 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 cannabis prior to using other drugs. In other words, rearranging the order of the alleged "steppingstones" did not change the outcomes.
As with cannabis, this correlation does not, however, necessarily mean that alcohol is a gateway drug (i.e. a causal relationship). In addition, whether one tries alcohol or cannabis first before the other does not accurately predict later substance use disorders.
One study found that, in the United States, raising the drinking age to 21 in the 1980s was correlated with an increase in cannabis use among high school seniors, the opposite of what the gateway theory would predict. This suggests that the two substances are substitutes rather than complements. Interestingly, state decriminalization of cannabis did not predict an increase in cannabis use; rather, it predicted a mild decrease in both alcohol and cannabis use. Higher alcohol prices, however, appeared to reduce the use of both substances, suggesting at least partial complementarity (though not necessarily a gateway).
, "People who abuse drugs are also likely to be cigarette smokers. More than two-thirds of drug abusers are regular tobacco smokers, a rate more than triple that of the rest of the population." One study found that cannabis use varies inversely with cigarette prices: the higher the cigarette price, the less cannabis use (though the association of cannabis use with later hard drug use was not robust). Another study found that adolescents (especially the youngest ones) who smoke are 50% more likely to have drinking problems than those who do not. Still another study finds that giving nicotine to early adolescent rats appears to increase the reinforcing (reward) effects of subsequent cocaine exposure, an effect that was not seen in adult rats. However, as with the Karolinska study on cannabis given to adolescent rats, extrapolation to humans is difficult.
The price and tax of tobacco, particularly cigarettes, has been inversely associated with not just cigarette consumption but also that of alcohol and cannabis. This suggests complementarity between tobacco and alcohol and between tobacco and cannabis, but not necessarily a gateway effect.
A more recent US-Finnish twin study found that those who started smoking tobacco by the age of 12 were 26 times more likely to start using cannabis or other illcit drugs by age 17, compared to those who never smoked. In fact, early tobacco smoking was one of the most powerful predictors of later use of illicit drugs.
and OxyContin, such substances have also been recently labeled as gateway drugs. In the US, such substances appear to be more common than cannabis as the first "illicit" drug tried, and are relatively easy to obtain by adolescents. Due to the similarity between narcotics, those who become addicted to prescription painkillers sometimes move on to heroin since the latter can actually be a cheaper habit to support. In addition, a study on mice found that abusing oxycodone during adolescence may sensitize the brain's reward system
, possibly predisposing to later addiction.
Caffeine
has also been alleged by some to be a gateway drug. Being the most widely consumed psychoactive substance in the world, it is often the first one that people use, preceding even alcohol or tobacco if the latter two are used. However, the hypothesis of caffeine being a gateway drug has not been very well studied, and thus there is little to no evidence either way on this question.
Cannabis use only predicted later nicotine dependence in non-dependent tobacco smokers who also used cannabis daily, and even for them cannabis had no significant effect on the likelihood of quitting tobacco.
An American study also found a modest association between earlier cannabis use and later daily smoking (and nicotine dependence) as well, specifically among those who had smoked at least one tobacco cigarette. However, the results were not always statistically significant, and said nothing about the risk of initiating tobacco use. The smoking of blunts was also not addressed.
On the other hand, a more recent Australian twin study casts doubt on the hypothesis of a truly causal relationship between early (or any) cannabis use and later nicotine dependence. Rather, it was found to be largely due to common genetic factors, with no remaining evidence for a reverse gateway effect.
Tobacco
Tobacco is an agricultural product processed from the leaves of plants in the genus Nicotiana. It can be consumed, used as a pesticide and, in the form of nicotine tartrate, used in some medicines...
, alcohol
Alcoholic beverage
An alcoholic beverage is a drink containing ethanol, commonly known as alcohol. Alcoholic beverages are divided into three general classes: beers, wines, and spirits. They are legally consumed in most countries, and over 100 countries have laws regulating their production, sale, and consumption...
, and cannabis
Cannabis (drug)
Cannabis, also known as marijuana among many other names, refers to any number of preparations of the Cannabis plant intended for use as a psychoactive drug or for medicinal purposes. The English term marijuana comes from the Mexican Spanish word marihuana...
.
While some research shows that many hard drug users used cannabis or alcohol before moving on to the harder substances, other research shows that some serious drug abusers have used other drugs before using cannabis or alcohol.
The former is particularly evident in individual drug-abuse histories which tend to show that "hard drug" users do progress from one drug to another.
Variations of the theory
Several different hypotheses have been called "gateway" theories in popular discourse. These include (but are not limited to):- The gateway substance causes users to be at increased risk for abuse of other substances.
- The gateway substance primes the brain for addiction to other substances (independent of becoming more likely to try other substances).
- A rigid sequence of progression, starting with licit drugs followed by (increasingly dangerous) illicit ones.
- The gateway effect is pharmacological, rather than socially constructed.
Cannabis
Some scientific studies show that the consumption of cannabisCannabis (drug)
Cannabis, also known as marijuana among many other names, refers to any number of preparations of the Cannabis plant intended for use as a psychoactive drug or for medicinal purposes. The English term marijuana comes from the Mexican Spanish word marihuana...
can possibly predict a significant higher risk for the subsequent use of other "harder" illicit drugs, while other studies show that it cannot. Two recent studies are from University of Pittsburgh
University of Pittsburgh
The University of Pittsburgh, commonly referred to as Pitt, is a state-related research university located in Pittsburgh, Pennsylvania, United States. Founded as Pittsburgh Academy in 1787 on what was then the American frontier, Pitt is one of the oldest continuously chartered institutions of...
's School of Pharmacy
University of Pittsburgh School of Pharmacy
The University of Pittsburgh School of Pharmacy is the graduate pharmacy school of the University of Pittsburgh in Pittsburgh, Pennsylvania, USA. Founded in 1878, it offers Doctor of Pharmacy and Doctor of Philosophy degrees, as well as a residency training program...
, and from Dr. Michael Lynskey.
Study of Australian Adolescents (10 years)
A stratified, random sample of 1,943 adolescents was recruited from secondary schools across Victoria, AustraliaAustralia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
at age 14–15 years. This cohort was interviewed on eight occasions until the age of 24–25 years. At age 24 years, 12% of the sample had used amphetamines in the past year, with 1%–2% using at least weekly. Young adult amphetamine use was predicted strongly by adolescent drug use and was associated robustly with other drug use and dependence in young adulthood. Associations were stronger for more frequent users. Among young adults who had not been using amphetamines at age 20 years, the strongest predictor of use at age 24 years was the use of other drugs, particularly cannabis, at 20 years. Those who were smoking cannabis at the age of 15 were as much as 15 times more likely to be using amphetamines in their early 20s.
Twin Study
A study by researchers at Virginia Commonwealth UniversityVirginia Commonwealth University
Virginia Commonwealth University is a public university located in Richmond, Virginia. It comprises two campuses in the Downtown Richmond area, the product of a merger between the Richmond Professional Institute and the Medical College of Virginia in 1968...
attempted to dissect the contribution of genetic, shared environmental and unique environmental influences on the development of dependence on other drugs in those who had used cannabis. The study found that while cannabis was strongly predictive of use of other drugs in the future, the main contributors to this effect were the shared environmental and genetic risk for all substances. However, there was "persisting evidence for some causal influences" of cannabis in the development of other drug dependencies, indicating that the gateway theory could be operative, although not the main cause of the association.
Study of rats
In 2006, the Karolinska Institute in SwedenSweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
used twelve rats to examine how adolescent use of cannabis affects subsequent abuse of other illicit drugs. The study gave six of the twelve "teenage" (28–49 days old, or 6.6–10.4 in human years) rats a small dose of THC
Tetrahydrocannabinol
Tetrahydrocannabinol , also known as delta-9-tetrahydrocannabinol , Δ1-THC , or dronabinol, is the main chemical psychoactive substance found in the cannabis plant. It was first isolated in 1964. In pure form, it is a glassy solid when cold, and becomes viscous and sticky if warmed...
, reportedly equivalent to one cannabis joint smoked by a human, every three days. The rats were allowed to self-administer heroin by pushing a lever and the study found the rats given THC took larger doses of heroin (but no such effect was found for amphetamines).
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 opiate
Opiate
In medicine, the term opiate describes any of the narcotic opioid alkaloids found as natural products in the opium poppy plant.-Overview:Opiates are so named because they are constituents or derivatives of constituents found in opium, which is processed from the latex sap of the opium poppy,...
s on rat's brain and thus causes them to use more heroin. Paul Armentano, policy analyst for NORML
National Organization for the Reform of Marijuana Laws (United States)
The National Organization for the Reform of Marijuana Laws is an American non-profit organization based in Washington, DC whose aim is to move public opinion sufficiently to achieve the legalization of non-medical marijuana in the United States so that the responsible use of cannabis by adults is...
, claimed because the rats were given THC at the young age of 28 days, is impossible to extrapolate the results of this study to humans. Also, the previously cannabis-exposed adult rats, despite being desensitized to heroin, were no more likely to get addicted (as measured by likelihood of self-administration) than the controls. In addition, not all animal studies agree with the results found in this study (see below).
Studies not in favor of the gateway theory
In 1999, a study by the Division of Neuroscience and Behavioral Health at the Institute of MedicineInstitute of Medicine
The Institute of Medicine is a not-for-profit, non-governmental American organization founded in 1970, under the congressional charter of the National Academy of Sciences...
entitled "Marijuana and Medicine: Assessing the Science Base," found no evidence of a link between cannabis use and the subsequent abuse of other illicit drugs on the basis of its particular physiological effect.
Mathematical Model
In December 2002, a study by RANDRAND
RAND Corporation is a nonprofit global policy think tank first formed to offer research and analysis to the United States armed forces by Douglas Aircraft Company. It is currently financed by the U.S. government and private endowment, corporations including the healthcare industry, universities...
regarding if cannabis use results in the subsequent use of cocaine
Cocaine
Cocaine is a crystalline tropane alkaloid that is obtained from the leaves of the coca plant. The name comes from "coca" in addition to the alkaloid suffix -ine, forming cocaine. It is a stimulant of the central nervous system, an appetite suppressant, and a topical anesthetic...
and heroin was published in the British Journal of Addiction, a peer-reviewed scientific publication. The researchers created a mathematical model simulating adolescent drug use. National rates of cannabis 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. Andrew Morral, associate director of RAND's Public Safety and Justice unit and lead author of the study stated:
One reason the risk factor for abusing drugs in cannabis users is higher is because few people try hard drugs prior to trying cannabis, not because cannabis users increasingly try hard drugs such as amphetamines. For example, cannabis is typically available at a significantly earlier age than other illicit drugs. Further research has shown that people with a disposition to resort to cannabis use are more likely to live longer and healthier lives than users of other "social drugs" such as alcohol.
Study on American adolescents (12 years)
In December 2006, a 12 year gateway drug hypothesis study on 214 boys from ages 10–12 by the American Psychiatric AssociationAmerican Psychiatric Association
The American Psychiatric Association is the main professional organization of psychiatrists and trainee psychiatrists in the United States, and the most influential worldwide. Its some 38,000 members are mainly American but some are international...
was published in the American Journal of Psychiatry
American Journal of Psychiatry
The American Journal of Psychiatry is a monthly peer-reviewed medical journal covering all aspects of psychiatry and the official journal of the American Psychiatric Association. The first volume was issued in 1844, at which time it was known as the American Journal of Insanity...
. The study concluded adolescents who used cannabis 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 cannabis prior to using other drugs. In other words, rearranging the order of the alleged "steppingstones" did not change the outcomes.
Study on San Francisco vs. Amsterdam
In 2004, a study comparing cannabis users in San Francisco to those in Amsterdam was done to test the effects of the differing drug policies in the two cities on drug use patterns. The Netherlands has a drug policy of decriminalization in which cannabis can be bought by adults over 18 in quasi-legal "coffee shops" and used publicly, while in the United States cannabis is criminalized and must be bought in the black market (often from the same dealers that sell hard drugs) and used "underground". The results found that, compared with their counterparts in Amsterdam the San Francisco cannabis users were significantly more likely to use cocaine, crack, amphetamines, ecstasy, and opiates despite similar cannabis use patterns and a more permissive drug policy in the Netherlands.Rat studies
A study in 3-4 month old rats actually found reduced reinforcing potential of cocaine in those rats pretreated with THC compared with those treated with vehicle only. Another rat study (age unspecified) found that, while rats pretreated with THC consumed higher doses of heroin relative to controls, both groups took up self-administration of heroin at the same rate, and there was no significant difference between groups on the reinforcing effects of heroin.Alcohol
Both alcohol and tobacco tend to precede cannabis use, and it is rare for those who use hard drugs to not have used alcohol or tobacco first. Data from the 2005 National Survey of Drug Use and Health (NSDUH) in the United States found that, compared with lifetime nondrinkers, adults who have consumed alcohol were statistically much more likely to currently use illicit drugs and/or abuse prescription drugs in the past year. Effects were strongest for cocaine (26 times more likely), cannabis (14 times more likely), and psychedelics (13 times more likely). In addition, lifetime drinkers were also six times more likely to abuse or be dependent on illicit drugs than lifetime nondrinkers.As with cannabis, this correlation does not, however, necessarily mean that alcohol is a gateway drug (i.e. a causal relationship). In addition, whether one tries alcohol or cannabis first before the other does not accurately predict later substance use disorders.
One study found that, in the United States, raising the drinking age to 21 in the 1980s was correlated with an increase in cannabis use among high school seniors, the opposite of what the gateway theory would predict. This suggests that the two substances are substitutes rather than complements. Interestingly, state decriminalization of cannabis did not predict an increase in cannabis use; rather, it predicted a mild decrease in both alcohol and cannabis use. Higher alcohol prices, however, appeared to reduce the use of both substances, suggesting at least partial complementarity (though not necessarily a gateway).
Tobacco
According to the NIDANational Institute on Drug Abuse
The National Institute on Drug Abuse is a United States federal-government research institute whose mission is to "lead the Nation in bringing the power of science to bear on drug abuse and addiction."-History:...
, "People who abuse drugs are also likely to be cigarette smokers. More than two-thirds of drug abusers are regular tobacco smokers, a rate more than triple that of the rest of the population." One study found that cannabis use varies inversely with cigarette prices: the higher the cigarette price, the less cannabis use (though the association of cannabis use with later hard drug use was not robust). Another study found that adolescents (especially the youngest ones) who smoke are 50% more likely to have drinking problems than those who do not. Still another study finds that giving nicotine to early adolescent rats appears to increase the reinforcing (reward) effects of subsequent cocaine exposure, an effect that was not seen in adult rats. However, as with the Karolinska study on cannabis given to adolescent rats, extrapolation to humans is difficult.
The price and tax of tobacco, particularly cigarettes, has been inversely associated with not just cigarette consumption but also that of alcohol and cannabis. This suggests complementarity between tobacco and alcohol and between tobacco and cannabis, but not necessarily a gateway effect.
A more recent US-Finnish twin study found that those who started smoking tobacco by the age of 12 were 26 times more likely to start using cannabis or other illcit drugs by age 17, compared to those who never smoked. In fact, early tobacco smoking was one of the most powerful predictors of later use of illicit drugs.
Other drugs sometimes alleged to be gateway drugs
Due to the past decade's increase in prescription drug abuse, especially narcotic painkillers such as VicodinVicodin
Hydrocodone/paracetamol is a combination of two analgesic products hydrocodone and paracetamol used to relieve moderate to severe pain...
and OxyContin, such substances have also been recently labeled as gateway drugs. In the US, such substances appear to be more common than cannabis as the first "illicit" drug tried, and are relatively easy to obtain by adolescents. Due to the similarity between narcotics, those who become addicted to prescription painkillers sometimes move on to heroin since the latter can actually be a cheaper habit to support. In addition, a study on mice found that abusing oxycodone during adolescence may sensitize the brain's reward system
Reward system
In neuroscience, the reward system is a collection of brain structures which attempts to regulate and control behavior by inducing pleasurable effects...
, possibly predisposing to later addiction.
Caffeine
Caffeine
Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants...
has also been alleged by some to be a gateway drug. Being the most widely consumed psychoactive substance in the world, it is often the first one that people use, preceding even alcohol or tobacco if the latter two are used. However, the hypothesis of caffeine being a gateway drug has not been very well studied, and thus there is little to no evidence either way on this question.
Reverse gateway
In addition, there is a less-studied reverse gateway theory that earlier regular cannabis use predicts later tobacco initiation and/or nicotine dependence in those who did not use tobacco before. One Australian study appears to have found such a correlation. However, they admittedly could not rule out the fact that cannabis is commonly (in many countries, including Australia and most of Europe) mixed with tobacco in joints to enhance burning and/or stretch supplies. Additionally, though not mentioned in the study, blunts (tobacco-leaf cigars filled with cannabis) are commonly used by some subcultures in the United States as well, despite tobacco-mixed joints being relatively uncommon there. Such "traditions," as opposed to cannabis per se, could plausibly act as a "Trojan horse" for developing a nicotine habit.Cannabis use only predicted later nicotine dependence in non-dependent tobacco smokers who also used cannabis daily, and even for them cannabis had no significant effect on the likelihood of quitting tobacco.
An American study also found a modest association between earlier cannabis use and later daily smoking (and nicotine dependence) as well, specifically among those who had smoked at least one tobacco cigarette. However, the results were not always statistically significant, and said nothing about the risk of initiating tobacco use. The smoking of blunts was also not addressed.
On the other hand, a more recent Australian twin study casts doubt on the hypothesis of a truly causal relationship between early (or any) cannabis use and later nicotine dependence. Rather, it was found to be largely due to common genetic factors, with no remaining evidence for a reverse gateway effect.
Criticism
The gateway theory has been criticized, mostly due to the existence of alternative explanations. These include (but are not limited to):- Some individuals are, for whatever reason, willing to try any substance, and the "gateway" drugs are merely the ones that are (usually) available at an earlier age than the harder drugs.
- Particularly for cannabis, which is illegal, exposure to the black market (where harder drugs are available) is suggested to be the real cause.
- For teenagers, credibility of adults is eroded when the dangers of the "gateway" drugs are exaggerated or made up, leading them to think all anti-drug messages are nonsense.
- The peer environments in which "gateway" drugs are used can sometimes overlap with the ones in which harder drugs are used, especially in societies that prohibit the substances or impose very high age limits.
External links
- "The Myth of Marijuana's Gateway Effect" from NORML (7 February 1995)
- The road to ruin? Sequences of initiation into drug use and offending by young people in Britain
- The classification of cannabis under the Misuse of Drugs Act 1971 (Section 4.6 "Does cannabis use lead on to other drug use?")
- How did the marijuana gateway myth get started? Schaffer Library of Drug Policy.