Summary: A large population-based study indicates that doxycycline, a commonly used antibiotic, is associated with a lower risk of developing schizophrenia when prescribed to adolescents attending mental health services. An analysis of more than 56,000 young patients found that those treated with doxycycline had a roughly 30–35% reduced chance of receiving a schizophrenia diagnosis in adulthood compared with peers who used other antibiotics.
Researchers propose this protective association may arise from doxycycline’s anti-inflammatory properties and its influence on synaptic pruning—processes important for brain development. While the findings are observational and require confirmation in clinical trials, they point to a promising avenue for early prevention strategies in high-risk youth.
Key Facts
- Protective Association: Adolescents prescribed doxycycline showed a 30–35% lower likelihood of developing schizophrenia as adults compared with those receiving other antibiotics.
- Biological Rationale: Doxycycline may reduce brain inflammation and modulate synaptic pruning, mechanisms implicated in schizophrenia development.
- Clinical Implications: If confirmed by trials, doxycycline or similar anti-inflammatory approaches could be repurposed as early preventive interventions for high-risk adolescents.
Source: University of Edinburgh
Overview
New research suggests a widely prescribed antibiotic might lower the risk that some adolescents go on to develop schizophrenia. Using nationwide healthcare records, researchers compared outcomes for young people who received doxycycline with those who used other antibiotics while under the care of child and adolescent mental health services.
The collaborative study—led by the University of Edinburgh with partners at the University of Oulu and University College Dublin—used advanced statistical methods on Finnish register data to assess long-term schizophrenia risk following antibiotic prescriptions in adolescence.
Schizophrenia is a serious psychiatric disorder that most commonly emerges in late adolescence or early adulthood and often involves hallucinations and delusions. Identifying preventive measures during the adolescent period, when many people first present to mental health services, could have important public-health implications.
The investigators analysed records for 56,395 individuals who had used antibiotics and attended adolescent mental health services. Of these, 16,189 (28.7%) had received doxycycline. After ten years of follow-up, the estimated schizophrenia risk for those who used non-doxycycline antibiotics was 2.1% (95% CI 1.9–2.3). In contrast, adolescents treated with doxycycline had lower risks across cumulative dose categories: low cumulative dose (risk 1.4%, risk ratio=0.70, 95% CI 0.48–0.85), medium cumulative dose (risk 1.4%, risk ratio=0.65, 95% CI 0.25–1.04), and high cumulative dose (risk 1.5%, risk ratio=0.70, 95% CI 0.43–0.97).
The authors explored potential confounding factors, including the possibility that doxycycline prescriptions were driven by acne treatment rather than by infections. Sensitivity analyses suggested the association was unlikely to be explained solely by such differences between groups.
Doxycycline is a broad-spectrum antibiotic commonly used for various infections and acne. Laboratory and preclinical studies have suggested it can dampen inflammatory responses in brain cells and affect synaptic pruning—the normal developmental process by which the brain refines neural connections. Excessive pruning has been linked in some research to the later emergence of schizophrenia, providing a plausible biological mechanism for the observed association.
Professor Ian Kelleher, the study lead and Professor of Child and Adolescent Psychiatry at the University of Edinburgh, noted that up to half of people who later develop schizophrenia have prior contact with child and adolescent mental health services for other problems. He emphasized that, although the study cannot prove causality because it is observational rather than randomized, the results warrant further investigation of doxycycline and other anti-inflammatory treatments as possible preventive options for adolescents at elevated risk of severe mental illness.
Key Questions Answered:
A: Adolescents treated with doxycycline were about 30–35% less likely to develop schizophrenia in adulthood compared with peers who received other antibiotics.
A: The drug appears to reduce brain inflammation and may influence synaptic pruning—the neural refinement process that, when excessive, has been linked to schizophrenia.
A: While observational, the findings point to the possibility that commonly available anti-inflammatory medications could be repurposed for prevention if randomized trials confirm efficacy and safety.
About this research
Author: Guy Atkinson
Source: University of Edinburgh
Contact: Guy Atkinson, University of Edinburgh
Image: Image credited to Neuroscience News
Original Research: Closed access. “Doxycycline Use in Adolescent Psychiatric Patients and Risk of Schizophrenia: An Emulated Target Trial” by Ian Kelleher et al., American Journal of Psychiatry.
Abstract
Doxycycline Use in Adolescent Psychiatric Patients and Risk of Schizophrenia: An Emulated Target Trial
Objective:
About half of people who develop psychosis have had prior contact with child and adolescent psychiatric services, indicating a window for potential preventive interventions. The authors hypothesised that exposure to doxycycline—an antibiotic with suggested neuroprotective and anti-inflammatory effects—during adolescence could be associated with a reduced risk of later schizophrenia.
Methods:
The study emulated a target trial using nationwide Finnish health register data for individuals born between 1987 and 1997 who attended adolescent psychiatric services between ages 13 and 18 and received any antibiotics. Participants were followed from their first dispensed antibiotic prescription until age 30, and the primary outcome was a recorded diagnosis of schizophrenia. The g-formula was applied to estimate schizophrenia risk across levels of cumulative doxycycline use (none; low <1,499 mg; medium 1,500–2,999 mg; high ≥3,000 mg) over different follow-up intervals.
Results:
Of 56,395 individuals who had used antibiotics and attended adolescent psychiatric services, 16,189 (28.7%) had used doxycycline. After 10 years, the schizophrenia risk was 2.1% (95% CI 1.9–2.3) for those who used non-doxycycline antibiotics. In contrast, the risk at 10 years was lower among doxycycline users across cumulative dose categories (low: 1.4%, risk ratio=0.70; medium: 1.4%, risk ratio=0.65; high: 1.5%, risk ratio=0.70).
Conclusions:
These results raise the tentative but potentially important possibility that doxycycline exposure during adolescence may be associated with a reduced risk of developing schizophrenia among patients seen by child and adolescent mental health services. Further randomized trials are needed to determine causality and to evaluate safety and effectiveness before any clinical recommendations can be made.