Cannabis is one of the most widely used substances in Australia. The “just say no” messaging of previous generations has clearly not translated into real-world behaviour – which makes open, informed conversations about its effects more important than ever. This is particularly relevant for those of us working with people experiencing anxiety, depression, and psychosis.
At Reconnect, we believe in honest, balanced, and evidence-based discussions – so let’s take a closer look at what the research actually tells us.
A Common Question
Over the years, a common argument has been raised: if cannabis increases the risk of schizophrenia, and only around 1% of the population develops this condition, why hasn’t that number increased significantly alongside rising cannabis use globally?
It’s a fair question – and the answer is nuanced. Research suggests that cannabis is not a sole cause of schizophrenia, but rather a risk factor that can contribute to the development of psychosis in vulnerable individuals. In other words, cannabis may act as a trigger or amplifier, rather than a root cause.
The Link Between Cannabis and Psychosis
A growing body of research shows a consistent association between cannabis use and psychosis – particularly among young people, individuals with a family history of mental illness, and those using high-potency, high-THC cannabis.
Regular use of high-THC cannabis has been linked to an increased likelihood of experiencing psychotic symptoms. In some cases, it may also contribute to the onset of a first episode of psychosis in individuals who were already vulnerable.
In my own work with clients, I’ve seen how cannabis – often used daily with the intention of managing stress or anxiety – can, over time, increase anxiety levels and destabilise mental health rather than provide the relief people were hoping for. I’ve also worked with occasional users who have experienced genuine benefits, finding it helpful for calming their nervous system and quieting a busy mind.
The reality is that everyone is different. Factors such as age, diet, unresolved emotional trauma, individual constitution, genetics, and a history of other substance use – including hallucinogens – all play a meaningful role in how cannabis affects a person’s mental health and wellbeing.
What the Research Shows
Large-scale studies, including those published in The Lancet Psychiatry, have found that daily use of high-potency cannabis is associated with a significantly increased risk of psychotic disorders, and that risk increases with both frequency of use and THC strength.
Weekly or more frequent use carries greater risk than occasional use, early use during adolescence is associated with higher vulnerability, and genetic predisposition plays a significant role in how individuals respond. A landmark study by Di Forti et al. (2019), published in The Lancet Psychiatry, found that daily users of high-potency cannabis were five times more likely to experience psychosis compared to non-users.
It’s important to recognise that generally cannabis today is significantly more potent than it was even twenty years ago. THC concentrations in many commercial products have increased dramatically, meaning comparisons to “a joint back in the day” are no longer particularly meaningful – the substance people are using today is fundamentally different.
Historical records suggest that Middle Eastern hashish from the 1970s-90s typically contained around 5–25% THC. It’s also worth noting that this hashish was produced from sun-grown (non-hydroponic), landrace (non-hybridised) cannabis varieties – some of which grew naturally without human intervention, including the addition of nutrients. This contrasts significantly with many of the hydroponically grown, high potency products available in dispensaries today.
The rise in high-potency products, including concentrates that can exceed 90% THC (often used for “dabbing”), further increases potential risk. These forms of cannabis have been associated with a higher likelihood of adverse mental health outcomes, particularly among young people.
Understanding Risk
One of the challenges in public health messaging is that advice is often vague – “moderation is the key” – without clearly defining what that actually means. Research suggests that risk is primarily shaped by three factors: frequency of use, THC potency, and individual vulnerability.
Higher-risk patterns tend to include daily or near-daily use, high-THC products (generally above 10–15% THC), early age of initiation, and a personal or family history of mental health conditions. Lower-risk approaches – while not entirely risk-free – generally involve infrequent use, avoiding high-potency products, and avoiding use during adolescence or periods of significant mental health vulnerability.
It’s also important to note that thinking in terms of “number of joints” can be misleading, as THC content varies enormously between products. At present, there is no clearly defined safe level of cannabis use, and individual responses can vary widely.
What This Means for You
This isn’t about judgment. Many people use cannabis to manage sleep, anxiety, or chronic pain – and those reasons are understandable. But if you or someone you care about is experiencing mental health challenges, it’s worth having an honest conversation with a GP or mental health professional about how cannabis may be impacting your overall wellbeing. The two things are rarely as separate as we’d like to believe.
Our Approach at Reconnect
At Reconnect Health Solutions, we take a holistic and non-judgmental approach to mental health support. If substance use is part of your story, we work alongside you – not against you – to find sustainable, meaningful ways to support your wellbeing. If you’d like to speak with someone, our team is here to help.
This blog is intended for educational purposes only and does not constitute medical advice. Please
consult your GP or qualified mental health professional for personalised guidance.
References
Frequency, Dose-Response & Potency
Di Forti, M., et al. (2019). The contribution of cannabis use to variation in the incidence of psychotic disorder across Europe (EU-GEI): a multicentre case-control study. The Lancet Psychiatry. https://www.thelancet.com
Kraan, T., et al. (2020). Factors Moderating the Association between Cannabis Use and Psychosis Risk: A Systematic Review. PubMed Central (PMC), National Institutes of Health. https://pmc.ncbi.nlm.nih.gov/articles/PMC7071602/
Schoeler, T., et al. (2016). Risk-thresholds for the association between frequency of cannabis use and the development of psychosis: a systematic review and meta-analysis. Psychological Medicine, Cambridge University Press. https://www.cambridge.org
Age of Initiation & Genetic Predisposition
Andréasson, S., et al. (1987). Cannabis and schizophrenia: a longitudinal study of Swedish conscripts. Originally cited in: Cannabis use and the risk of developing a psychotic disorder. PMC, National Institutes of Health. https://pmc.ncbi.nlm.nih.gov/articles/PMC2424288/
Guloksuz, S., et al. (2021). Cannabis, schizophrenia genetic risk, and psychotic experiences: a cross-sectional study of 109,308 participants from the UK Biobank. Translational Psychiatry (Nature). https://www.nature.com/articles/s41398-021-01330-w
Centre for Addiction and Mental Health (CAMH). Genetic predisposition to schizophrenia may increase risk of psychosis from cannabis use. https://www.camh.ca
Yale School of Medicine. Behind the Smoke: Unmasking the Link Between Cannabis and Schizophrenia. https://medicine.yale.edu
High-Potency Cannabis & Concentrates
Hindley, G., et al. (2020). Psychosis and high-potency cannabis: a review. Frontiers in Psychiatry.
https://www.frontiersin.org/journals/psychiatry/articles/10.3389/fpsyt.2014.00054/full
