A team of scientists led by an Edinburgh professor of psychiatry says a commonly prescribed antibiotic could help reduce the risk of some young people developing schizophrenia.

A paper by researchers from Scotland, Finland and Ireland, published today in the American Journal of Psychiatry, reports that patients using adolescent mental health services who were treated with the antibiotic doxycycline were significantly less likely to go on to develop schizophrenia in adulthood compared with patients treated with other antibiotics.

The authors say the findings highlight the potential to repurpose an existing, widely used medication as a preventive intervention for schizophrenia, a severe mental disorder that typically emerges in early adulthood and is often associated with hallucinations and delusional beliefs.

Researchers at the University of Edinburgh, working alongside colleagues at the University of Oulu in Finland and University College Dublin, applied advanced statistical modelling to large-scale healthcare register data from Finland.

Analysing data from more than 56,000 adolescents attending mental health services who had been prescribed antibiotics, they observed that those treated with doxycycline had a 30–35% lower risk of developing schizophrenia than peers who received other antibiotics.

One theory is that the protective effect could be linked to doxycycline’s impact on inflammation and brain development.

Study lead, Professor of Child and Adolescent Psychiatry at the University of Edinburgh, Ian Kelleher, said the study fundings are promising:

“As many as half of the people who develop schizophrenia had previously attended child and adolescent mental health services for other mental health problems.

“At present, though, we don’t have any interventions that are known to reduce the risk of going on to develop schizophrenia in these young people. That makes these findings exciting.

“Because the study was observational in nature and not a randomised controlled trial, it means we can’t draw firm conclusions on causality, but this is an important signal to further investigate the protective effect of doxycycline and other anti-inflammatory treatments in adolescent psychiatry patients as a way to potentially reduce the risk of developing severe mental illness in adulthood.”

Doxycycline is a broad-spectrum antibiotic commonly used to treat infections and acne. Previous studies suggest it can reduce inflammation in brain cells and influence synaptic 'pruning' – a natural process where the brain refines its neural connections. Excessive pruning has been associated with the development of schizophrenia.

The researchers say they undertook further analyses to show that the lower risk wasn’t simply because the young people had been treated for acne rather than having infections, and to try to rule out other hidden differences between the groups.

Read more: Partnership urges action over Scotland’s mental health; Childhood adversity health impacts felt at 50 revealed; Edinburgh brain mapping could hold key to diseases

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