UK Study: 68% of First-Episode Schizophrenia Patients Had Lifetime Drug Use, Cannabis Linked to Earlier Onset | Research

The takeaway

In 152 recent-onset schizophrenia patients from inner-city London, 68% reported lifetime substance use (mostly cannabis), and cannabis use independently predicted earlier onset of psychosis after adjusting for alcohol and other drugs.

Read this if you want to understand the relationship between cannabis use and the timing of schizophrenia onset in a UK population.

68% of first-episode schizophrenia patients had lifetime substance use, mostly cannabis

What the researchers found

Researchers studied 152 people recruited to the West London First-Episode Schizophrenia Study. Sixty percent were smokers, 27% reported alcohol problems, 35% reported current substance use (excluding alcohol), and 68% reported lifetime substance use, with cannabis and psychostimulants most commonly used.

Cannabis use and gender had independent effects on age at onset of psychosis, even after adjusting for alcohol misuse and use of other drugs. This means the cannabis-earlier onset association was not explained by general substance use patterns.

The authors noted the bidirectional nature of the finding: the strong association between cannabis use and earlier psychosis onset could mean either that cannabis precipitates schizophrenia or that early-onset symptoms are themselves a risk factor for cannabis use.

Why it matters

This UK inner-city study replicated findings from other countries showing cannabis use is associated with earlier schizophrenia onset. The careful adjustment for alcohol and other drugs strengthens the case that cannabis has a specific association with onset timing rather than being a marker of general substance use.

The numbers in context

152 patients studied. 60% smokers. 27% alcohol problems. 35% current substance use. 68% lifetime substance use. Cannabis and psychostimulants most common. Cannabis and gender independently predicted earlier onset after adjusting for alcohol and other drugs.

How the study worked

Cross-sectional study of 152 participants in the West London First-Episode Schizophrenia Study. Self-reported data on drug and alcohol use collected alongside information on age at onset. Mental state, cognition (IQ, memory, executive function), and social function were assessed.

What this study cannot tell us

Cross-sectional design cannot determine causation or temporal sequence. Self-reported drug use may underestimate actual use. Inner-city London sample may not represent other populations. The study could not determine whether cannabis precipitated psychosis in people who would not otherwise have developed it.

How to read the evidence

Cross-sectional study from a well-characterized first-episode cohort. Good statistical adjustment for confounders but cannot establish causation.

When this study was published

Published in 2006. The association between cannabis use and earlier schizophrenia onset has been consistently replicated in subsequent studies.

The bigger picture

This study adds to a consistent international pattern showing cannabis use is associated with earlier onset of schizophrenia. The acknowledgment that the relationship could be bidirectional (cannabis causing earlier onset, or early symptoms increasing cannabis use) reflects the nuanced understanding that has developed in this field.

Questions still open

Does preventing cannabis use delay psychosis onset in at-risk individuals? Is the earlier onset associated with cannabis use linked to worse long-term outcomes?

Common questions

How common is cannabis use among people with first-episode schizophrenia?

In this UK inner-city sample, 68% reported lifetime substance use, with cannabis being one of the most commonly used substances alongside psychostimulants. Thirty-five percent reported current substance use.

Does cannabis definitely cause earlier schizophrenia?

This study found cannabis use independently predicted earlier onset, but acknowledged the relationship could work both ways: cannabis might precipitate psychosis, or early-onset symptoms might make someone more likely to use cannabis. The cross-sectional design cannot determine which direction is correct.

Read the original research

Comorbid substance use and age at onset of schizophrenia.

The British journal of psychiatry : the journal of mental science, 188, 237-42

View on PubMed ↗

Citation

Barnes, Thomas R E; Mutsatsa, Stanley H; Hutton, Sam B; Watt, Hilary C; Joyce, Eileen M. (2006). Comorbid substance use and age at onset of schizophrenia.. The British journal of psychiatry : the journal of mental science, 188, 237-42.