Experts say the findings highlight the potential to repurpose an existing, widely used medication as a preventive intervention for severe mental illness.
Schizophrenia is a severe mental disorder that typically emerges in early adulthood and is often associated with hallucinations and delusional beliefs.
To better understand potential ways of preventing the condition, researchers from the University of Edinburgh, in collaboration with the University of Oulu and University College Dublin, applied advanced statistical modelling to large-scale healthcare register data from Finland.
The team analysed data from more than 56,000 adolescents attending mental health services who had been prescribed antibiotics. They found that those treated with doxycycline had a 30–35 per cent lower risk of developing schizophrenia than peers who received other antibiotics.
The researchers hypothesised that the protective effect could be linked to doxycycline’s impact on inflammation and brain development.
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.
Further analyses showed that the lower risk wasn’t simply because the young people may have been treated for acne rather than having infections, and was unlikely to be explained by other hidden differences between the groups.
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.”
Reference: Ulla Lång, Johanna Metsälä, Hugh Ramsay, Fiona Boland, Katriina Heikkilä, Anna Pulakka, Anne Lawlor, Karen O’Connor, Juha Veijola, Eero Kajantie, Colm Healy, and Ian Kelleher,Common antibiotic may reduce schizophrenia risk, study shows, American Journal of Psychiatry, DOI 10.1176/appi.ajp.20240958
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