Cannabis and Psychosis: Separating Risk from Rhetoric — What Clinicians Need to Know

Key considerations 

The relationship between cannabis and psychosis has been studied for decades, but interpreting it requires care.

Psychosis can be used to describe symptoms such as hallucinations, delusions, and disordered thinking, an acute substance-induced episode, or symptoms occurring as part of a longer-term disorder such as schizophrenia.

Likewise, “cannabis use” can mean anything from occasional exposure to sustained daily consumption of high-THC products.

These distinctions are particularly important as some of the strongest evidence published on cannabis and psychosis points towards a dose-response relationship.

It’s also worth noting that much of the existing research has been focused on illegally sourced cannabis and recreational use, so a cautious approach should be applied when considering the findings in the context of prescribed cannabis-based products for medicinal use (CBPMs). 

What is cannabis-induced psychosis?

Cannabis can produce a range of psychological side effects, including anxiety, transient paranoia and other psychotic symptoms.

Cannabis-induced psychotic disorder describes a clinically significant episode of psychosis associated with cannabis exposure. Symptoms may continue beyond the period of acute intoxication and require clinical assessment and treatment.

Cannabis-induced psychosis may also indicate a substantial vulnerability to future illness. A 2020 systematic review and meta-analysis examined 50 studies involving more than 40,000 people with substance-induced or other brief psychoses. 

Among people specifically diagnosed with cannabis-induced psychosis, 34% were subsequently diagnosed with schizophrenia based on six studies involving 3,040 people.

Although the study focused on recreational use rather than medical use, clinicians prescribing CBPMs should ensure patients receive appropriate psychiatric assessment after an episode of suspected cannabis-induced psychosis.

Does the risk increase with THC potency and dose?

Research suggests that frequency of use, how much is consumed, and the concentration of delta-9-tetrahydrocannabinol (THC) are all relevant when assessing the risks of cannabis-induced psychosis. 

THC is the principal intoxicating cannabinoid in cannabis and most closely associated with its acute psychoactive effects.

In a 2022 systematic review published in The Lancet Psychiatry examining 20 studies exploring cannabis potency and mental-health outcomes, eight investigated psychosis, with the overall evidence suggesting that higher-potency cannabis is associated with increased risk of psychosis and cannabis use disorder compared with lower-potency products.

In the UK Cannabis & Me study, which surveyed more than 3,000 adults with current or previous cannabis use, higher THC consumption was also associated with higher paranoia scores. 

Can CBD reduce the risk of psychosis?

While it is sometimes suggested that cannabidiol (CBD), THC’s non-psychoactive counterpart, can moderate these effects, the evidence is less certain. 

In a 2020 systematic review and meta-analysis published in The Lancet Psychiatry examined experimental studies in which THC was administered to healthy participants were examined. Acute THC administration was associated with increases in positive psychiatric symptoms, including psychosis-like symptoms, as well as negative and general psychiatric symptoms.

In the same review, only four studies examined CBD alongside THC, with inconsistent evidence that CBD reduced THC-induced psychiatric symptoms.

Who is more vulnerable to cannabis-induced psychosis?

The research suggests that the risk of cannabis-induced psychosis appears to be heterogeneous. The same exposure may not carry the same implications for every patient.

Personal or family history of psychosis, earlier initiation of cannabis use, frequent and high-THC consumption, problematic use, and exposure to other psychological and environmental risk factors may all be relevant.

The Cannabis and Me study found that participants who reported initially using cannabis to self-medicate anxiety, depression, or other forms of discomfort also tended to consume cannabis more frequently and had higher levels of THC exposure, which were in turn associated with higher levels of paranoia. 

Genetics is also an increasingly important area of research.

In 2026, researchers at King’s College London’s Institute of Psychiatry, Psychology & Neuroscience reported new findings examining the biological relationship between cannabis use disorder and psychosis. Using large-scale genetic datasets, the researchers identified more than 500 genetic loci associated with a broad psychosis phenotype, including 122 previously unreported associations.

They also identified overlap between biological pathways associated with psychosis and cannabis use disorder.

Professor Marta Di Forti, Professor of Drug Use, Genetics and Psychosis at King’s IoPPN and senior author of the study, said the findings could eventually contribute to identifying those most vulnerable to harm.

However, there is currently no routine genetic test that can tell a clinician whether an individual patient will develop cannabis-related psychosis.

Does prescribed medical cannabis carry the same risks as recreational cannabis?

Much of the strongest epidemiological research into cannabis and psychotic disorders has examined recreational or non-medical cannabis use. 

It cannot be assumed that risk estimates derived from those populations apply directly to patients receiving cannabis-based medicinal products under clinical supervision.

Prescribed products have defined cannabinoid content and are supplied within a regulated framework. Patients are screened before treatment, given specific dosing instructions, and monitored over time.

However, medical use does not mean that high-THC exposure is inherently risk-free.

Patients using cannabis for the treatment of a medical condition or symptom management routinely use higher doses of cannabis, more frequently, and are more likely to use it long-term.

The evidence base specifically examining psychosis outcomes among UK medical cannabis patients remains limited. As with all medications, prescribing clinicians will need to make a risk-benefit decision balancing any risks with the potential benefits to the patient. 

What warning signs should clinicians monitor?

Some adverse effects are easier to identify than others. 

Clinicians should be aware of any new or worsening paranoia, unusual beliefs, perceptual disturbances, hallucinations, thought disturbance and significant changes in behaviour or functioning.

Changes in the way a patient uses cannabis may be equally important, such as escalating consumption, increasing reliance on higher-THC products, or signs of dependence.

NICE guidance for people with psychosis and coexisting substance misuse recommends reviewing changes in patterns of substance use alongside changes in mental and physical state, circumstances and treatment. Where psychosis is suspected, NICE recommends referral to secondary mental-health services for assessment and management.

In its Good Practice Guide, the Medical Cannabis Clinicians Society (MCCS) recommends treatment be reconsidered or discontinued where there is “no meaningful clinical benefit despite appropriate titration and duration of treatment, side effects are unacceptable or outweigh the clinical benefit, there are concerns regarding safety, misuse, or adherence, or the patient is unable to follow the treatment plan safely or consistently”.

How can clinicians balance potential benefit and risk?

The majority of people exposed to cannabis do not develop a psychotic disorder, and many patients report benefits from CBPMs for psychiatric conditons.

In a 2026 survey of 6,282 UK medical cannabis patients across four clinics, 5,128 were being prescribed cannabis for anxiety, depression or PTSD. Among that subgroup, 97.6% reported improvement in symptoms, while more than 90% reported improvements in sleep and day-to-day functioning.

However, there is not enough evidence to reliably predict the outcome for an individual patient. For clinicians prescribing CBPMs, this uncertainty makes patient selection, informed consent, appropriate dosing, and ongoing monitoring even more important. 

Di Forti previously told Cannabis Health that the message is not that patients should be prevented from seeking this treatment, but that cannabis should be used with “support and monitoring” and attention to the balance and concentration of THC.

According to the MCCS guidelines, the most significant contraindication to THC-containing CBPMs is a history of psychosis or schizophrenia, particularly where this is current, recent, or unstable. 

Prescribing in this group requires a clear and structured risk assessment, evidence of stability over time, consideration of specialist psychiatric input, two-way communication between other prescribers working with the patient, and enhanced monitoring and follow-up. 

The MCCS also recommends peer review for first prescriptions over 2g flower/day and 25% and above THC levels, and any emergence of concerning or difficult side effects.

 

Frequently asked questions

Can cannabis cause psychosis?

THC can acutely produce psychosis-like symptoms in controlled studies, while cannabis use is associated with increased risk of psychotic disorders in epidemiological research. The relationship is influenced by factors including frequency, THC exposure and individual vulnerability. Cannabis use does not mean that a person will inevitably develop psychosis.

Is high-THC cannabis more likely to cause psychosis?

Studies consistently associate frequent use of high-potency cannabis with greater psychosis risk than lower levels of exposure. However, potency alone does not determine someone’s dose: the quantity consumed, frequency, and route of administration also affect total THC exposure.

Who is most at risk of cannabis-related psychosis?

Research suggests vulnerability may be influenced by several overlapping factors, including frequent or high-THC exposure, previous psychotic symptoms, younger age of initiation, problematic cannabis use, genetic vulnerability, and some environmental factors such as trauma. There is currently no test that can accurately predict an individual’s risk.

Can CBD prevent THC-induced psychosis?

There is not currently enough consistent evidence to conclude that CBD reliably prevents the psychiatric effects of THC. Some experimental research has explored a potentially moderating effect, but findings have been mixed.

Can prescribed medical cannabis cause psychotic symptoms?

Prescribed cannabis can contain THC, which has been shown experimentally to produce acute psychiatric symptoms. However, much of the epidemiological evidence on psychotic disorders comes from recreational cannabis populations, so risk estimates cannot simply be transferred directly to appropriately screened and monitored medical patients.

Should someone with a history of psychosis be prescribed medical cannabis?

A history of psychosis requires careful specialist assessment of potential risks and benefits. Decisions should take account of the person’s psychiatric history, current mental state, other substance use, proposed cannabinoid exposure and existing clinical care. Where psychosis is suspected, NICE recommends assessment through appropriate secondary mental-health services.