Scientists have discovered a potential new use for a widely prescribed antibiotic: reducing the risk of schizophrenia in adolescents receiving mental health care. A recent study published in theAmerican Journal of Psychiatryanalyzed health records from more than 56,000 young psychiatric patients in Finland and found that those treated with doxycycline were 30-35% less likely to develop schizophrenia later in life compared to peers given other antibiotics. Schizophrenia is a severe mental health disorder that most commonly emerges in early adulthood and is marked by hallucinations, delusions, and disorganized thinking. Preventing its onset has been a key goal for mental health research, especially in adolescents attending psychiatric services who are at elevated risk. The collaborative study, led by researchers from the University of Edinburgh along with colleagues from the University of Oulu and University College Dublin, used advanced statistical models on comprehensive Finnish healthcare data. They tracked antibiotic prescriptions and subsequent schizophrenia diagnoses over many years, comparing risk among adolescents prescribed doxycycline—a broad-spectrum antibiotic widely used for infections and acne—with those receiving other antibiotics. Confounding factors were rigorously addressed to isolate doxycycline’s impact. The research showed a significantly reduced risk of schizophrenia among doxycycline users, consistent across different dosage levels. Further analyses suggested this effect was unlikely due to acne treatment alone or hidden differences between groups. The authors hypothesize doxycycline’s neuroprotective role stems from its anti-inflammatory properties and influence on synaptic pruning—a brain developmental process implicated in schizophrenia when dysregulated. Lead investigator Professor Ian Kelleher emphasized that while these observational findings cannot confirm causality, they provide a promising new direction for preventive therapies targeting inflammation in high-risk youth. The study highlights the potential to repurpose existing medications in adolescent psychiatry to mitigate severe mental illnesses, calling for future randomized controlled trials to validate doxycycline’s protective effect. This discovery opens exciting possibilities for early intervention to reduce lifelong schizophrenia burden through safe, accessible treatments. REFERENCE: Ulla Lång, Johanna Metsälä, Hugh Ramsay, Fiona Boland, Katriina Heikkilä, Anna Pulakka, Anne Lawlor, Karen O’Connor, Juha Veijola, Eero Kajantie, Colm Healy, Ian Kelleher. Doxycycline Use in Adolescent Psychiatric Patients and Risk of Schizophrenia: An Emulated Target Trial. American Journal of Psychiatry, 2025; DOI: 10.1176/appi.ajp.20240958