Cannabis in adolescence - is it still a risk factor for psychosis and schizophrenia?

It's news week again at the daily doctor - what's been on the news?

It's that time again — so many health and medical news reports hitting the airwaves — time to digest the news with the daily doctor!

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Capitalism making hay from health care

It’s a tale as old as capitalism.

There is money to be made prescribing medicinal cannabis so money is made prescribing medicinal cannabis.

And so Elise Worthington and Celina Edmonds, ABC news, reported last Wednesday that:¹

“[Australia’s health practitioner regulator] AHPRA has taken action against 57 medical practitioners, pharmacists and nurses over medicinal cannabis prescribing practices.

“[…] AHPRA chief executive Justin Untersteiner said the regulator was investigating a further 60 practitioners.”

It has never been faster, easier and more lucrative to use an algorithm or AI to prescribe medicinal cannabis. You only need a checklist for the patient to complete in their own time then an approved precriber to sign off if the legal requirements are met.

More concerning is the report that:

“The regulator said some businesses were using ‘aggressive and sometimes misleading advertising that targets vulnerable people’ and online questionnaires that coached patients to say ‘the right thing’ to justify prescribing.”

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What you can take away from today’s daily doctor

The article has a lot of good health information to level up your health literacy, including:

“The new AHPRA guidelines explicitly state that except for childhood epilepsy, muscle spasms and pain associated with multiple sclerosis, cancer and chemotherapy-induced nausea and vomiting, ‘there is little evidence to support the use of medicinal cannabis’."

“According to Therapeutic Goods Administration (TGA) data, the main conditions medicinal cannabis is being prescribed for include insomnia, chronic pain and anxiety.”

and

“Most medicinal cannabis products prescribed in Australia are unapproved, meaning they have not been assessed by the TGA for safety, quality, performance or effectiveness, something patients must now be informed of during consultations.”

Of interest,

“The investigations also revealed concerns from doctors who said they were being treated like drug dealers and pressured to write medicinal cannabis scripts by the telehealth companies.”

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Marijuana, cannabis and cannabinoids

The term “cannabis” refers to the entire plant including both hemp and marijuana. The plant contains cannabinoid compounds (“cannabinoids”) that include those prescribed as medicine (“medicinal cannabis”).

There are two main types of medicinal cannabis that are prescribed: THC (“tetrahydrocannabinol”) and CBD (“cannabidiol”).

• THC has psychoactive effects that may be prescribed for nausea, vomiting, pain, appetite stimulation and other rarer and more specific medical conditions. They are the ones sought for recreational purposes.

• CBD doesn’t have the psychoactive effects and are prescribed for seizures as well as pain and anxiety. There is research showing CBD may be used to treat psychosis and/or schizophrenia.²

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What is going through your doctor’s head?

Medical school dogma from at least two decades back is, marijuana use in adolescence — especially in young male users — increases the risk of psychosis and/or schizophrenia developing in later life.

Psychosis is a symptom, schizophrenia a mental health condition / diagnosis. Psychosis is a major or primary symptom in schizophrenia.

Much research into cannabis over the past two decades have backed this dogma, now fact:

A large Danish cohort study on cannabis use disorder and schizophrenia published in 2023³ found that

• “Young males might be particularly susceptible to the effects of cannabis on schizophrenia.”

• “At a population level, assuming causality, one-fifth of cases of schizophrenia among young males might be prevented by averting [cannabis use disorder].”

Two recent meta-analyses confirmed use of cannabis in adolescence increases the risk for psychosis. One was published in 2021,⁴ the other in 2016, which concluded that:⁵

“Current evidence shows that high levels of cannabis use increase the risk of psychotic outcomes and confirms a dose-response relationship between the level of use and the risk for psychosis.”

Most of your doctors from GPs to non-GP specialists will not have an interest beyond this, in cannabinoids or medicinal cannabis.

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What may your doctor also know if they have an interest in the field?

A 2020 meta-analysis⁶ proposes that

“we can conclude that the tetrahydrocannabinol (THC) component of cannabis can be the main culprit causing psychosis and schizophrenia in the at-risk population.”

A 2024 review in a journal with a much higher impact factor⁷ summarises the mystery that is this plant of mysteries thusly:

“It is well-established that the delta-9-tetrahydrocannabinol (delta-9-THC) component of cannabis elicits psychotomimetic effects at high doses;

• worsens schizophrenia-related psychosis;

• commonly develops into cannabis use disorder in individuals with schizophrenia; and

• increases the risk of earlier-onset schizophrenia symptoms in those harboring genetic susceptibility.”

“However, individuals with schizophrenia commonly use cannabis and cannabis derivatives such as cannabidiol (CBD).

• These products seem to alleviate psychotic symptoms and relieve adverse side effects of antipsychotic medications.

• Therefore, one notion that has gained traction is the potential utility of cannabis-derived cannabidiol (CBD) as adjunct treatment to reduce schizophrenia-associated psychosis and other symptoms.”

“Currently, preclinical and clinical data remain inconclusive.”

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As an aside, the Marconi 2016 paper confirmed that we still don’t know for certain the mechanism by which cannabis affects the risk of psychosis (and schizophrenia) in young people:

“Although this meta-analysis shows a strong and consistent association between cannabis use and psychosis, a causal link cannot be unequivocally established.”

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And while we are on asides, it is worthwhile noting much of the published research - even over more than twenty years - is not racially and/or ethnically diverse. Most of this research cannot be generalised to the global population.

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1. Elise Worthington and Celina Edmonds, ABC news. AHPRA takes action against more than 50 practitioners in medicinal cannabis crackdown. <https://www.abc.net.au/news/2025-07-09/medicinal-cannabis-regulations-ahpra-/105506828> Published Jul 9, 2025. Accessed Jul 15, 2025.

2. McGuire P, Robson P, Cubala WJ et al. Cannabidiol (CBD) as an Adjunctive Therapy in Schizophrenia: A Multicenter Randomized Controlled Trial. Am J Psychiatry, 2018; 175(3): 225-31.

3. Hjorthøj C, Compton W, Starzer M et al. Association between cannabis use disorder and schizophrenia stronger in young males than in females. Psychol Med, 2023; 53(15): 7322-28.

4. Kiburi SK, Molebatsi K, Ntlantsana V et al. Cannabis use in adolescence and risk of psychosis: Are there factors that moderate this relationship? A systematic review and meta-analysis. Subst Abus, 2021; 42(4): 527-42.

5. Marconi A, Di Forti M, Lewis CM et al. Meta-analysis of the Association Between the Level of Cannabis Use and Risk of Psychosis. Schizophr Bull, 2016;42(5): 1262-9.

6. Patel S, Khan S, M S, Hamid P. The Association Between Cannabis Use and Schizophrenia: Causative or Curative? A Systematic Review. Cureus, 2020; 12(7): e9309.

7. Johnson K, Weldon AJ, Burmeister MA. Differential effects of cannabis constituents on schizophrenia-related psychosis: a rationale for incorporating cannabidiol into a schizophrenia therapeutic regimen. Front Psychiatry, 2024; 15: 1386263.