Question

Discuss the statement “Marijuana is a gateway drug that leads to the use of harder drugs such as cocaine and heroin” in terms of what you have learned about the criteria of causation and threats to the validity of causal inference. What are some alternative explanations?

Answer 1

• Gateways drugs used in early adolescence were significantly associated with marijuana use, illegal drugs and cocaine in older adolescence, but over time these relationships were not consistent in adulthood. Changes in the pattern of psychoactive drug use were important predictors of drug use in adulthood.
• The concept of “gateway hypothesis” has been studied since the 1970s as the theory suggests that an adolescent's early experimentation with alcohol or tobacco or cannabis escalates to more addictive illicit drugs later in adulthood. Most commonly used illicit substances include heroin/opioids, cocaine and or amphetamines and their designer drug analogs, considered illegal by the criminal justice system in the United States and other jurisdictions.
• The gateway hypothesis says marijuana inspires users to try other drugs: Once they get a taste of how fun marijuana is, they're more likely to want to see how fun other drugs are. So if marijuana is more easily available through legalization, believers of the hypothesis say, it could push people to harder drugs.But this is an empirical claim one that can be verified or refuted by research. So far, there's no solid evidence to support the gateway hypothesis. And there's some evidence that legalizing marijuana may actually reduce the use of other drugs.
• Marijuana use is positively correlated with alcohol use and cigarette use, as well as illegal drugs like cocaine and methamphetamine. This does not mean that everyone who uses marijuana will transition to using heroin or other drugs, but it does mean that people who use marijuana also consume more, not less, legal and illegal drugs than do people who do not use marijuana.
• People who are addicted to marijuana are three times more likely to be addicted to heroin.
• It's true that marijuana use correlates with harder drug use. But so does alcohol and tobacco use. There doesn't have to be a causal link between marijuana or alcohol and harder drugs to explain this; it could just be that the things that drive someone to marijuana or alcohol, boredom, depression, social circles can just as easily drive them to other drugs. Perhaps the correlation is actually exposing those underlying factors, not some gateway effect.
• People start with marijuana and alcohol before harder drugs because they are much more accessible, because they're generally cheaper than harder drugs and part of much bigger markets.
  
• In the sense that marijuana use typically precedes rather than follows initiation of other illicit drug use, it is indeed a "gateway" drug. But because underage smoking and alcohol use typically precede marijuana use, marijuana is not the most common, and is rarely the first, "gateway" to illicit drug use. There is no conclusive evidence that the drug effects of marijuana are causally linked to the subsequent abuse of other illicit drugs.
• So there is no good causal evidence for the gateway hypothesis. There is some weak correlational evidence, but it can be easily support with an entirely different idea drug users tend to start with more accessible drugs over the gateway hypothesis.That doesn't rule out the gateway effect entirely. But it should give proponents of it pause.
• Several studies have found that medical marijuana legalization can actually reduce opioid deaths, perhaps because patients can use pot to treat their chronic pain without the risk of overdose and less of a risk for addiction instead of highly addictive, deadly opioids.
• Similarly, marijuana legalization also may lead people to substitute their alcohol use with marijuana use. This could be hugely beneficial to public health and safety, since alcohol is a fairly dangerous drug linked to violent crimes, poisonings, and fatal accidents, while legal pot isn't linked to violent crimes or poisonings and less likely to cause accidents.
• Putting all of this together, there's no good evidence that marijuana is a "gateway drug" or that any gateway effect would be worsened by legalization. The evidence suggests, in fact, that marijuana could stop some people from using harder, more dangerous drugs if it was legalized.
• None of this means marijuana is harmless. Its potential risks include dependence and overuse, accidents, non-deadly overdoses that lead to mental anguish and anxiety, and marijuana use potentially causing psychotic episodes.But the gateway hypothesis isn't supported by the evidence.