Cannabis Made Clear

Is Cannabis a Gateway Drug?

Some people believe cannabis can lead to other drugs, but what does the research say?

Gateway Theory

Does cannabis lead to consuming other substances? This idea — known as the gateway theory or gateway hypothesis — has been around since the 1970s. But does it hold any merit given what we know today?

What is the gateway theory?

Researcher Denise Kandel first proposed the gateway hypothesis in 1975. Its basic premise is that most people who use illegal drugs viewed as higher risk (such as cocaine, heroin or methamphetamine) began experimenting with legal or more readily available substances like alcohol, tobacco and cannabis first.

This theory proposed a type of causal pathway for understanding drug use initiation and progression. In popular culture, the gateway theory has been translated into the idea that if someone (usually a young person) starts using cannabis, they will inevitably transition to using illicit higher-risk drugs, and to problematic use.

Problematic or illicit higher-risk drug use can be loosely defined as drug use that negatively affects a person’s health, safety or relationships, causes addictive behaviour or jeopardizes their social or legal status.

Simply put, the way we commonly use and understand the gateway theory now is that the consumption of cannabis, tobacco or alcohol acts as a “gateway” to illicit higher-risk drugs. These legal or more readily available substances are often seen as normalizing — or making acceptable — the use of illicit higher-risk drugs.

Although cannabis wasn’t the first or only drug Kandel and later researchers identified as a gateway substance, at the time it was the first illegal drug named in the sequence. Significantly, this happened at the height of North America’s war on drugs, and politicians and legislators often used the gateway theory to justify criminalizing cannabis.

Is the gateway theory correct?

Worldwide data indicates a link between initial cannabis consumption and later illegal drug use. It is uncommon to find someone who consumes illicit higher-risk drugs who hasn’t tried cannabis, alcohol or tobacco first.

However, it’s important to note that though a demonstrable relationship exists between two things — in this case, prior cannabis consumption and later illicit higher-risk drug use — it doesn’t mean one is causing or is caused by the other. In fact, most people who consume cannabis do not progress to illicit higher-risk drugs. It is more accurate to say that alcohol, cannabis and tobacco (and increasingly vapes) are the substances that are widely available in many communities, which means that many people, especially youth or young adults, experiment with these first when they have access.

Why the gateway theory may not be accurate
Nowadays, it’s easy for Canadian adults to buy legal cannabis, but when cannabis was still unregulated, purchasing it from illegal sources raised the likelihood of encountering illicit higher-risk drugs. The thought was that the same source selling illegal cannabis may also be selling illicit higher-risk drugs. Eliminating that exposure is one of the reasons the Government of Canada chose legalization.

Access to illegal drugs doesn’t mean people will try them. Access and experimentation are also not equivalent to problematic use. A 2015 probability study found that fewer than half of lifelong cannabis consumers and less than 10% of newer consumers are likely to try illicit higher-risk drugs.

Many potential social and biological influences are at play when someone turns to illicit higher-risk drugs, and each person’s reason or mix of reasons is unique to them and their circumstances. It’s also important to note that experimentation with drugs is not equivalent to problematic use.

Some factors associated with illicit higher-risk drug use include:

  • adverse life experiences, including childhood trauma
  • anxiety, depression and post-traumatic stress
  • boredom
  • lack of opportunity
  • socioeconomic status
  • genetics
  • family and peer influences
  • access to drugs

The list above is just a sample of influences that can appear before, after or during risky drug use. Researchers call them confounding variables — factors that affect both cause and effect. A question raised in 2015 by researchers at the Canadian Centre on Substance Abuse illustrates how confounding variables blur the cause-and-effect relationship in studies:

“Did the psychosocial or health problem exist before the cannabis use and increase the risk of cannabis use? Did cannabis use lead to the psychosocial or health problem? Or was there a common factor that led to both the psychosocial or health problem and the cannabis use?”

Do any drugs fit the gateway theory model?

Cannabis, alcohol and tobacco are all associated with subsequent drug use in observational and epidemiological studies — studies that draw conclusions by observing what’s happening in existing social environments or among particular populations. But data on the biochemical or molecular mechanisms around drug use and addiction tell different stories.

Over the years, Denise Kandel has stressed that cannabis wasn’t the sole gateway substance in her theory. Recently, she teamed up with her partner, biochemist and biophysicist Eric R. Kandel, to investigate nicotine. By blending epidemiological reviews with biologic investigations in mice and rats, they found that nicotine primes the brain for other drugs, enhancing the effects of cocaine and increasing addictive behaviours. Similarly, a rat study found that prior alcohol use increased the likelihood of cocaine addiction.

When studies first began with THC (an active ingredient in cannabis), the results varied. A 2013 study found that rats exposed to THC valued nicotine rewards more than control rats who hadn’t been exposed, but this effect didn’t occur in earlier experiments when THC came before heroin or cocaine. Interestingly, another rat study found that pre-exposure to THC actually reduced cocaine seeking.

It’s important to note one of the major flaws in the gateway theory: cannabis is a more easily accessible substance with a lower harm and risk profile than many other substances. Therefore, along with alcohol and tobacco, cannabis is among the common initiating substances. Nevertheless, most cannabis users never progress to illicit higher-risk drug use, and it’s likely that a range of factors contribute to whether someone does — and if they do, whether they will then progress to problematic use.

As for alcohol, studies are less certain. Alcohol has been shown to both enhance and block the effects of other drugs and medications. Heavy and early drinking is associated with a laundry list of health and social risks. But as with cannabis, the cause and effect of it all isn’t clear, and animal studies on the gateway effects of alcohol have produced mixed results.

Short story? If there is a gateway drug, the biological research has nicotine as the top contender. However, illicit higher-risk drug use is a complex issue, and we don’t fully understand the motivations and mechanisms behind addiction and risky behaviour in human societies.

The evidence does not support a causal pathway from cannabis to subsequent illicit higher-risk drug use, but that doesn’t mean it’s benign or safe for everyone.

Get the facts on responsible consumption and access a wide variety of cannabis-related information on the Cannabis Made Clear online education hub.

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Denise Kandel's classic work on the gateway sequence of drug acquisition
The Effects of Cannabis Use during Adolescence
Alcohol's Effects on Health
Is cannabis a “gateway drug”?
Risk of Using Other Drugs
A Rat Model of Cocaine-Alcohol Polysubstance Use Reveals Altered Cocaine Seeking and Glutamate Levels in the Nucleus Accumbens
Prior exposure to THC increases the addictive effects of nicotine in rats
Prior alcohol use enhances vulnerability to compulsive cocaine self-administration by promoting degradation of HDAC4 and HDAC5
Confounding Variable
Prior Exposure to Alcohol Has No Effect on Cocaine Self-Administration and Relapse in Rats: Evidence from a Rat Model that Does Not Support the Gateway Hypothesis
Is Drug Addiction Genetic?
Common liability to addiction and “gateway hypothesis”: Theoretical, empirical and evolutionary perspective
What is Epidemiology?
Why Nicotine is a Gateway Drug
Her influential ‘gateway hypothesis’ changed the way we think about addiction
A Molecular Basis for Nicotine as a Gateway Drug
Setting The Record Straight On The Phrase 'Gateway Drug'
The Gateway Hypothesis of substance abuse: developmental, biological and societal perspectives
Common liability to addiction and “gateway hypothesis”: Theoretical, empirical and evolutionary perspective
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