Research links cannabis use, particularly frequent or high-THC exposure, with increased risk of psychotic disorders. The evidence is consistent with an important contributory role, while the precise pathway and individual susceptibility vary. Many cannabis users do not develop schizophrenia, and many people with schizophrenia have not used cannabis.
Cannabis contains compounds with different effects, particularly THC and CBD. Its relationship with psychosis depends on factors such as exposure, potency, individual susceptibility and the outcome studied. Cannabis is not the explanation for every psychotic illness, but it is a clinically important factor to assess respectfully and accurately rather than through blame or reassurance unsupported by evidence.
Association is not a personal prediction or proof that one exposure caused one diagnosis. Studies must consider confounding, timing and whether emerging symptoms influence use. These complexities do not justify ignoring the relationship. Public explanations should distinguish relative risk from absolute probability and avoid presenting one statistic without its comparison group. Clinically, the aim is an informed discussion about exposure and vulnerability, including the person’s own experience, rather than a deterministic claim that cannabis always causes schizophrenia or that only people with a known family history need to consider risk.
Relative risk compares groups, while absolute risk describes the proportion affected over a period. Both are needed to interpret an association. A large relative increase can still concern a minority, and a population figure cannot identify the cause of one person’s illness. This statistical distinction allows risk to be taken seriously without presenting it as certainty for every individual.
Further reading: National Institute of Mental Health; World Health Organization; National Institute on Drug Abuse.
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