Commonly-prescribed antibiotic may reduce schizophrenia risk, study finds

A commonly-prescribed antibiotic could help reduce the risk of some young people developing schizophrenia, researchers have found.

An international team involving scientists at the University of Edinburgh made the discovery by analysing large-scale healthcare register data from Finland.

The team examined data from more than 56,000 adolescents attending mental health services who had been prescribed antibiotics.

They found that those who had been treated with the antibiotic doxycycline had a 30-35% lower risk of developing schizophrenia than peers who received other antibiotics.

Doxycycline is a “broad-spectrum” antibiotic commonly used to treat infections and acne, with the team saying its effect in relation to schizophrenia may be linked to its impact on inflammation and brain development.

Previous studies suggest doxycycline 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, which is a severe mental disorder that typically emerges in early adulthood and is often associated with hallucinations and delusional beliefs.

The team described the findings as “exciting”, and said they highlight the potential to repurpose an existing, widely used medication as a preventive measure for severe mental illness.

Professor Ian Kelleher, study lead and professor of child and adolescent psychiatry at the University of Edinburgh, said: “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.”

The study involved researchers from the University of Edinburgh, the University of Oulu, University College Dublin, and St John of God Hospitaller Services Group, and was funded by the Health Research Board.

It is published in the American Journal of Psychiatry.