A large Finnish registry study suggests that doxycycline, an antibiotic widely used for acne, may lower the risk of schizophrenia among adolescents receiving mental health care, with teens prescribed the drug showing roughly a 30–35% reduced risk compared with peers given other antibiotics.
Scientists from the University of Edinburgh, the University of Oulu, and University College Dublin examined national Finnish health records for more than 56,000 adolescents who had been prescribed antibiotics while attending adolescent psychiatric services. The study, published in the American Journal of Psychiatry, found that those treated with doxycycline were about one-third less likely to develop schizophrenia later in life than those given other antibiotics. (ed.ac.uk)
The analysis used an emulated target trial design on individuals born in 1987–1997, following them from their first dispensed antibiotic prescription up to age 30. Of 56,395 eligible adolescents, 16,189 (about 29%) had used doxycycline. At 10 years, schizophrenia risk was 2.1% among those who received non‑doxycycline antibiotics versus 1.4–1.5% among those exposed to doxycycline, corresponding to relative risk reductions of roughly 30–35%. (pubmed.ncbi.nlm.nih.gov)
Researchers say a plausible explanation is doxycycline’s anti‑inflammatory action and potential effects on synaptic pruning, the brain’s process of refining neural connections during development; excessive pruning has been linked to schizophrenia. The team also reported that the findings were unlikely to be explained by acne treatment versus infection treatment or by other hidden group differences. (ed.ac.uk)
“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,” said Professor Ian Kelleher, the study’s lead author and Professor of Child and Adolescent Psychiatry at the University of Edinburgh. (ed.ac.uk)
Kelleher cautioned that the work is observational, not a randomized controlled trial, so it cannot establish causality—a point echoed by independent experts, who note that additional research will be needed to confirm whether doxycycline itself reduces risk. (ed.ac.uk)
The international collaboration included partners from St John of God Hospitaller Services Group, and the study received funding from the Health Research Board. (ed.ac.uk)
