Understanding Marijuana as a Gateway Drug

Alan Markwood
June, 2012


Confusion about whether a “gateway” effect is part of young people’s development of substance use is not surprising, given the wide variety of interpretations of “gateway effect.” Also, in discussions of gateway drug use marijuana plays a key role, and marijuana itself is widely misunderstood. Some clarification is needed, starting with marijuana and then the concept of gateway drug use.

Perceptions of Marijuana

There are a number of aspects of marijuana that have been poorly understood or misunderstood. A number of reasons can be given for such misunderstandings, including:

1. Increase in average potency of marijuana over the past 3-4 decades. The potency of marijuana’s primary psychoactive ingredient, THC (tetrahydroannabinol), has at least doubled in the past fifteen years. Going back thirty years, the potency of marijuana typically smoked in the U.S. may have been a third or less of average current potency. Effects of the drug that were imperceptible or mild for most users in the 1970s and 1980s are becoming more severe and more common.

2. Efforts by legalization advocates to present marijuana as being relatively harmless. Advocacy for legalizing marijuana cannot succeed unless marijuana is believed to have only mild negative effects (at worst) on marijuana users and on communities as a whole. So, whenever advocacy for marijuana legalization is prevalent, along with it come statements minimizing the magnitude of any problems associated with marijuana use.

3. Differences between marijuana’s method of acting and the more common patterns of other illicit drugs. Marijuana is a fat-soluble drug, unlike most others typically used. Rather than just circulating in the bloodstream, and quickly clearing from the body after use, THC is absorbed into fatty tissue in various parts of the body, and only slowly is eliminated. Four relatively unique effects based on this are the lingering effects, potential for unending effects, low overdose impact, and blunting of withdrawal symptoms.

a. Lingering Effects: Studies have shown that while a perceived “high” from marijuana may last about two hours after use, residual impairments of various skills can linger up to 24 hours.

b. Potential for Unending Effects: With a half-life of 3-4 days after using marijuana, THC can actually be continually affecting a person if the person’s rate of marijuana use exceeds their rate of elimination of THC from their body..

c. Low Overdose Impact: Because THC goes partly into fatty tissue rather than all circulating in the blood, there is typically little permanent damage from a single heavy dose, and marijuana overdose deaths don’t occur.

d. Blunting of Withdrawal Symptoms: Because THC is eliminated so slowly from the body, symptoms of withdrawal when marijuana use stops can be less

apparent than is the case for some other drugs. This has contributed to a perception of lack of addictive potential, but as average THC content has increased, withdrawal symptoms have become more common. Scientifically, the fact that some users become addicted has been established beyond doubt. As stated by NIDA (the National Institute on Drug Abuse), “Estimates from research suggest that about 9 percent of users become addicted to marijuana; this number increases among those who start young (to about 17 percent) and among daily users (25-50 percent).”

4. Impact of marijuana on users’ perception, memories, and judgment/decision-making skills. The hallmark short-term effects of marijuana use include “distorted perceptions, memory impairments, and difficulty thinking and solving problems” (NIDA). So, if a marijuana user (especially one with frequent and/or heavy use) is asked during or after use about any negative effects, they often may have forgotten or not noticed in the first place any decrease in mental skills under the influence. The accuracy of self-reports about marijuana use is spotty, and omissions are likely, even if the person giving the report is himself/herself convinced of its accuracy.

Gateway Phenomenon Described

One aspect of marijuana use that has been consistently misunderstood has to do with the ways that it does or doesn’t function as a “gateway” drug. Before discussing how it does function as a gateway drug, and implications of that, let’s review some of the many ways in which one’s definition of “gateway” may not apply to marijuana.

* If gateway means that marijuana is typically the first drug used, marijuana isn’t a gateway drug. Alcohol would better fit that definition.

* If gateway means that marijuana is always the first drug used among all “scheduled” (controlled) drugs, marijuana isn’t a gateway drug. Marijuana is very often the first illicit drug used by those who use one or more illicit drugs, but some others can also be common. During the past decade, the number of instances of prescription drugs being the first controlled substance used (with alcohol and tobacco not being included in the definition of “controlled substance”) has grown rapidly, apparently due to the rapid growth of prescriptions for narcotic drugs.

* If gateway means that marijuana is always in a sequence that starts with alcohol or tobacco, then marijuana, and then other drugs … marijuana isn’t a gateway drug. That sequence is common, but so are a few others.

* If gateway means that most young people who use marijuana go on to use other drugs, marijuana is not a gateway drug. The truth is that although hardly anyone starts use of a “post-gateway” drug like cocaine, meth, or heroin without having already used either alcohol, tobacco, marijuana, or some combination among those three gateway drugs, the majority of young people who have used marijuana will not go on to other illicit drugs. The real gateway effect isn’t that everyone who reaches a gate goes through it, but that: 1) Any who have reached the other side are very likely to have come through a gate, and 2) Any who turn away before reaching the gate are extremely unlikely to later find themselves beyond the gated wall. In other words, 1) Most of the people who use cocaine, meth, or

heroin (or some other “post-gateway” illicit drugs) have used marijuana, either concurrently or previously, and 2) Among the people who have never used marijuana, use of any “post-gateway” drugs is extremely rare.

Does this description of “gateway drug use” mean something important enough to merit sorting through all the potential confusion in order to understand it? I’d say it does. First, I’d define a gateway drug as the first drug of abuse used regularly (at least once a month) by a young person who begins regular use of a substance. That definition fits across most times and places, while the following two sentences are more specific to the United States and to the past ten years. A person’s gateway drug could be alcohol, tobacco, marijuana, or inhalants. Rarely it could be some other drug, particularly a prescription or over the counter drug used for psychoactive effect rather than as directed.

The current prevalence of teen use of each of the listed substances in the United States gives an indication of the relative role of each as a gateway drug, even though the picture is complicated by the many instances of multi-drug use. According to the national “Monitoring the Future” findings, the “30-day prevalence of use” by 10th grade students in 2011 for: alcohol was 27.2%; tobacco/cigarettes was 11.8%; tobacco/smokeless was 6.6%; marijuana was 17.6%; and for inhalants was 1.7%. Youth use of tobacco used to be (in the 1990’s) consistently between the alcohol prevalence and marijuana prevalence, but youth tobacco use decreased a great deal in the past decade, while teen use of marijuana decreased until about five years ago and has since risen.

Now, revisit the statement that,

“The real gateway effect isn’t that everyone who reaches a gate goes through it, but that: 1) Any who have reached the other side are very likely to have come through a gate, and 2) Any who turn away before reaching the gate are extremely unlikely to later find themselves beyond the gated wall.”

Although quantifying “extremely” can vary according to things like what’s defined as the “gateway” substance(s), or the population studied, the percentages are usually more than 90% and often near 99%. As an example, consider data from a 2002 study by the U.S. Dept. of Human Services, Substance Abuse and Mental Health Services Administration, Office of Applied Studies (Gfroerer, J. C., Wu, L.-T., & Penne, M. A. (2002). Initiation of Marijuana Use: Trends, Patterns, and Implications (Analytic Series: A-17, DHHS Publication No. SMA 02-3711). Rockville, MD: Substance Abuse and Mental Health Services Administration, Office of Applied Studies.) In this study, the “gateway” was only marijuana use, and among the results studied were the extent to which age at first marijuana use was related to later use of either heroin, cocaine, or “any psychotherapeutic” (prescription) drug used “non-medically”. These results were based on information from adults age 26 or older who participated in the government’s main national survey of adult substance use. Two of the findings shown in the results were:

1. Among adults who had never used marijuana, only 0.1% (that is, one-tenth of a percent) had used heroin, only 0.6% had used cocaine, and only 5.1% had used prescription drugs for non-medical (i.e., “recreational”) effect.

2. For each substance (heroin, cocaine, or prescription drugs used for subjective effect rather than medically), there was consistently a pattern of decreasing

prevalence of use as age of first marijuana use categories went from “14 or younger” to “15-17”, then “18-20”, then “21 or older”, and finally “never used marijuana.” In regard to cocaine use, for example, the percent of people who had used cocaine, among the people who started marijuana use at age 14 or younger, was 62.0%. Looking at all who started marijuana use at ages 15-17; then 18-20; then 21 or older; and finally those who had never used marijuana, the respective percent who used cocaine went from 40.9% to 28.8%, then 16.4%, and finally 0.6% among those who never used marijuana.

In this particular example, “Any who turn away before reaching the gate are extremely unlikely to later find themselves beyond the gated wall,” means that only 0.6% of those who had never used marijuana later used cocaine (343,021 divided by 57,170,147). And, “Any who have reached the other side are very likely to have come through a gate” means that of the 1,341,359 adults who had used cocaine in their lifetime, nearly 75% (998,338) had previously used marijuana.

Gateway Phenomenon Applied

The prevalence of alcohol use and of other drug use increases as a cohort of youth (e.g., those born between 1995 and 1998) move through their junior high and high school years. During those years, alcohol, tobacco and marijuana are the drugs most prevalent among youth, but the majority of youth don’t regularly (at least once a month) use any of those gateway substances. Of those who do regularly use at least one, most use only one. However, regular use of just one raises the odds of use of a second, and each additional drug used raises the odds that even more will be used. In other words, drug use raises the odds of more drug use. What is behind this pattern of use?

Once a single gateway substance is regularly used, a number of potential risks based on use of that substance can strongly affect whether regular use of a second (or third, etc.) substance is begun. Here is one list of many possible ways that regular use of one gateway substance can increase risk of other drug use:

1. The lack of observed major negative effects on oneself and on peers who are using a substance can seem to validate a young person’s perception that trying to get high isn’t as dangerous as many adults warn it is. Some youths may recognize that heavy use of a substance or use of more than one substance raises the risk, but other youths may not see this.

2. Even if risk is perceived, it can be overtaken by the appeal of repeating a “high”, especially to the extent that dependency is developing. The sensation of being high can be extremely motivating, especially to persons more vulnerable to that effect. An extension of this is that in some instances regular use of one substance may chemically “prime” the brain for use of other substances that affect the brain similarly. The existence of this kind of “priming” has been documented, but how often this happens is not yet known.

3. When a young person connects with a substance-using peer group:

a. His/her perception of peer norms can be skewed toward drug use.

b. His/her access to a variety of substances may be facilitated by the group.

4. Depending on the interaction of a) substance(s) used; b) user vulnerability; and c) frequency of use, gateway substance use can impair key aspects of thought involved in decision making about other drug use. Marijuana is particularly suited to this effect due to the combination of its subtle, yet measurable impact on thought and the longer amount of time it remains in a person, compared to drugs that aren’t fat-based.

With the above discussion in mind, consider one key question about marijuana’s role as a gateway drug: Given that there is some gateway effect between marijuana use and use of other drugs, is that effect due to marijuana use causing increased risk of other substances (whether chemically or via situational factors such as interaction with other drug users), or due to marijuana use being an indicator of a young person who, for other reasons, is at elevated risk for a variety of problems? Recent research (e.g., “Is It Important to Prevent Early Exposure to Drugs and Alcohol Among Adolescents?”, Odgers et al, Pscyhological Science, v 19, n10, pp 1037-1044) shows that both are true: Some youth have problems early in life that put them at future risk of multiple other problems, but:

1) An equal (or greater) number of youth don’t have such problems, but become likely to have other youth or adult problems if they begin substance use at an early age.

2) Youth who are already at higher risk due to problems early in life and who begin substance use early in adolescence become even higher risk for a variety of problems.

3) The above observations hold true even if just alcohol is used by young teens, but the effects are worse for those with “poly-substance” (usually alcohol and marijuana) use.

So, regarding causation, research results suggest the following:

1. Some youth are more at risk of multi-substance use even before they start regular use of a gateway drug, but their risk increases with regular use of a gateway substance.

2. Three dimensions of youth alcohol, marijuana, or other gateway substance use that can greatly heighten the probability of multi-substance use, drug dependence, and a number of other problems are how early in life the regular use begins, how frequently the substance is used, and how heavy a “dose” is typically used.

3. The earlier that a teen or pre-teen starts use of marijuana (or alcohol), and the heavier and more frequent their use, the greater the likelihood that their rapidly increasing risk of multi-substance use and other problems is at least partly (and perhaps substantially) caused by the gateway substance use.

The term “causation” as used in this discussion doesn’t mean that use of one gateway substance dooms a person to using additional drugs: typically more youth do not progress to other drug use than do. However, for many who do progress, use of the first substance and the results of that use often can make the difference. The most typical pattern is alcohol as the first substance, but marijuana can be that first substance and in many cases is at least the first illicit drug used. In either case, marijuana use serves as a potential gate to other use. Most youth may not proceed through that gate, but the percent of marijuana users among those who go on is very high. So is the percent of alcohol users. The odds multiply if both those substances are used. Some people may prefer to say that marijuana

use “can contribute to risk for other drug use,” to emphasize that there are multiple factors involved, and that marijuana use certainly doesn’t guarantee any further use of any drug. Such a view is most appropriate when considering one person’s experiences. There is variation among individuals, so in regard to any one person, the role of marijuana use in the development of other drug use may not be clear. However, when large groups of young people are considered, there is no doubt that increases in marijuana use will result in more use of other drugs among that group or population. Increased marijuana use causes much of the increase in other drug use, by multiplying the risk already present at the start of regular use of marijuana.

In the 1970’s public opinion about marijuana was biased toward the negative. Today, with the (previously discussed) confusion about marijuana effects, public opinion is becoming very biased in the other direction. The toll taken on individuals and on society by marijuana use is growing at the same time public perception of individual and societal damage from marijuana is decreasing. One of the least well understood aspects of marijuana’s potential effect on individuals and marijuana’s measurable negative effect on communities is the way in which marijuana use can play a causal role in the development of other substance use. It is not “the” cause of other use, but is one of the most powerful contributing causes, in terms of increased risk to the individual and increased damage to populations. Marijuana users and others in favor of allowing use may continue to deny this gateway effect, but their denials don’t invalidate the consistent findings of objective study of population-wide substance use patterns.

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