Fact Check: Is Legalization Harming Teens' Mental Health?

If you read this January 10 Wall Street Journal article, you might conclude that a wave of cannabis-induced psychosis among teenagers is sweeping the country. The story highlights research into the connection between cannabis use and conditions such as schizophrenia and bipolar disorder. It suggests that access to high-potency cannabis is leading to ever-increasing rates of psychosis among teenagers.

But the actual data paints a different picture. Population studies of over 63 million people show that legalization does not increase the rate of psychosis. Marijuana use rates among youth are actually declining. And our best scientific evidence suggests that genetic factors – not cannabis use – are responsible for the connection between cannabis and psychosis.

Can cannabis really cause lifelong psychotic states – or is this just another example of a confusing correlation with causation, a common cause of “refrigerator madness”?

Research on cannabis and psychosis is nuanced, but definitely shows a strong correlation – as opposed to causation – between the two. For example, the data clearly shows that acute cannabis exposure can cause you to see vivid colors, mishear sounds, or become anxious. These experiences have been described as temporary “psychosis-like” episodes – particularly in occasional users.

Confusing correlation with causation

Given this, it is perhaps not surprising that when teenagers who use cannabis develop persistent psychosis-related conditions, their doctors and loved ones jump to the conclusion that cannabis is the cause of the change. There are numerous stories of teenagers who used cannabis and were subsequently diagnosed with these difficult, lifelong conditions. Statistically, people who use cannabis are more likely to develop bipolar disorder or schizophrenia than the general population.

But scientists have long been concerned with the question of whether cannabis use actually causes these diseases – or whether a third factor causes both. Based on cases in which these disorders occur after cannabis use, researchers estimate that cannabis-induced psychosis occurs in 0.0027% of users. But even with this exceptionally rare frequency, relevant studies cannot prove whether cannabis is the cause of psychosis or not.

There are many ways to interpret the data linking cannabis to psychosis. For example, people with psychotic disorders may be more likely to use cannabis as a form of self-medication. If this were true, it would result in the same strong correlation.


Has legalizing cannabis improved a state's mental health?

Other correlations: alcohol, tobacco

Cannabis is certainly not the only factor associated with psychosis, although it is receiving more attention. Studies have found that many things are linked to a higher risk of psychosis, including the use of any recreational substances such as alcohol and tobacco. These substances are used by schizophrenics at a similar rate as cannabis and show a similar statistical increase in the risk of psychosis. However, no one is discussing whether we should ban these substances.

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Life stressors

Stress is also often accompanied by psychosis. The stress associated with an event, such as a teenager leaving home to start college, can trigger a first psychotic episode.

A review study found that the strongest factors associated with the development of persistent psychosis are a) living in an urban area and b) belonging to an ethnic minority. Since cannabis is often used to combat stress, it is possible that people who are so stressed that they develop psychosis are more likely to turn to cannabis.

Spice, K-2 and designer drugs

Finally, studies linking cannabis to psychosis do not specify which specific cannabinoids are at play. For example, companies like head shops and truck stops sell unlicensed, unregulated – and often illegal – synthetic cannabinoids (THC-O, THC-P, HHC, etc.) that can be hundreds of times more powerful than THC alone.

The use of dangerous synthetic substances like Spice is widespread in states where there is no access to legal herbal THC. Sports and military THC testing systems also lead players and military personnel to look for new, dangerous synthetic drugs that don't show up on a drug test.

Data suggests that the use of synthetic cannabinoids may cause more symptoms of psychosis than natural cannabis.

Cannabis use survey, cannabis use among adolescents(Iuliia Kanivets, CSA Printstock/iStock)

Legalization does not lead to an increase in consumption by young people

Some research also suggests that cannabis use among teenagers in particular has a strong association with later diagnosis of a psychosis-related illness. This could mean that teenagers are particularly vulnerable to the effects of cannabis. But it could also suggest that conditions such as bipolar disorder and schizophrenia are most commonly recognized and diagnosed in the 20s, while cannabis use typically begins in the teens. It is possible that individuals with these conditions are more likely to self-medicate with cannabis; Since this typically occurs before their diagnosis, doctors and scientists assume that cannabis caused the psychosis-like condition.

While many prohibitionists would use the possibility of psychosis in teenagers as a reason to limit cannabis legalization, it is important to note that rates of cannabis use among teenagers are decreasing, not increasing, as states legalize cannabis. Street vendors do not check ID, but legitimate pharmacies do. This means that legalization tends to limit, rather than expand, teen access.


Cannabis legalization and teenage use: What do studies tell us?

The rate of psychosis *does not* increase with the legalization of cannabis

Fortunately, scientists go deeper than simple correlation studies. For example, they are studying the frequency of psychosis in places where cannabis is more available. If the spread of cannabis causes psychosis, it would follow that as access to cannabis increases, we would also see increasing rates of psychosis.

While legalization increases the incidence of other disorders directly caused by cannabis use, such as cannabinoid hyperemesis syndrome, studies examining the incidence of psychosis have yielded very mixed results.

The WSJ article mentioned earlier in this article cites a small Danish study that examined data from 6,788 people in 11 locations across Europe and Brazil. None had access to tested, legal cannabis.

While a link has been found between access to high-potency cannabis and psychosis, a much larger US study of over 63 million people found that access to medical or recreational cannabis had no impact at all on rates of psychosis. If we were to experience a dramatic surge in adolescent psychosis in the United States, as suggested in the recent WSJ article, that shift should be reflected in this large-scale population study.


CDC finds that youth hospitalizations for marijuana have decreased by 50% following legalization

Genetics can influence both cannabis use and mental health outcomes

Rates of psychosis have not skyrocketed with the recent increase in legal cannabis access. So why do we see a connection between the two?

Beyond the possibilities suggested above, genetics could play a key role. Scientists have found data that points to underlying genes that predispose someone to both psychosis and cannabis use disorders. (Doctors diagnose cannabis use disorder when someone experiences negative effects from cannabis use, wants to stop using it, but cannot bring themselves to do so despite repeated efforts.)

Research reports have found that a person whose genetic makeup is linked to cannabis use disorder may be more likely to develop schizophrenia, regardless of whether or not they have actually ever used cannabis. This suggests that genetics, not cannabis, is responsible.

One of the best-designed studies has just been published. In January, researchers published a rare study of more than 4,000 identical twins over time. One twin consumed weed and the other didn't, and the researchers tracked them for 27 years. Weed consumption had no impact on mental health outcomes.

“Cannabis use did not predict within-couple differences in psychoticism.”

Zellers, 2024, Journal of Psychopathology and Clinical Science

“Cannabis use did not predict differences in psychoticism within a couple,” the researchers concluded.

This brings up an important insight: If you have a family history of mental illness and your cannabis use is increasing, you may want to reconsider your habits.

The data also supports maintaining 21 as the legal appropriate age for cannabis use; This typically occurs towards the end of the phase in which a person may develop a congenital mental illness.

While further research could change our understanding of these issues, current data does not suggest that cannabis use is a strong causative factor for chronic mental illness. However, given cannabis' ability to cause visual effects or strange thoughts, THC is best avoided by those at risk. At the same time, doctors are actively examining whether the cannabinoid CBD is suitable for treating mental illnesses.

As always, consult a cannabis-specialist physician before beginning the medical use of cannabis to treat your symptoms.

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