Common antibiotic may lower schizophrenia risks, study finds

A common antibiotic may help lower the risk of some young people developing schizophrenia, a new study suggests.

Teenagers undergoing mental health treatment who were prescribed the antibiotic doxycycline were 30 per cent to 35 per cent less likely to develop schizophrenia in adulthood compared with teenagers who were treated with other antibiotics, according to the study, which was published in the American Journal of Psychiatry.

The research team described the results as “tentative but exciting”.

Schizophrenia affects approximately 23 million people worldwide. It causes psychosis marked by delusional beliefs, hallucinations, disorganised thinking, and other cognitive problems, which can be disabling.

The mental disorder typically emerges in early adulthood, and while it can be managed with medication, there is no cure.

The study included more than 56,000 adolescents in Finland, including more than 16,000 who were prescribed doxycycline, which is commonly used to treat infections and acne.

It was not a randomised trial, meaning it cannot prove that doxycycline actually prevents schizophrenia.

But the researchers believe the drug may help by reducing inflammation in the brain and influencing synaptic pruning, which is when the brain removes neurons and synapses it does not need. Abnormal synaptic pruning has been linked to schizophrenia.

The findings are “an important signal to further investigate the protective effect of doxycycline and other anti-inflammatory treatments in adolescent psychiatry patients,” Ian Kelleher, the study’s lead author and a professor of child and adolescent psychiatry at the University of Edinburgh, said in a statement.

He added that this approach could “potentially reduce the risk of developing severe mental illness in adulthood”.

However, independent experts cautioned against drawing concrete conclusions from the study, saying additional research would be needed to confirm any link between doxycycline and schizophrenia.

Dominic Oliver, a psychiatry researcher at the University of Oxford, noted that “many other treatments have shown early promise and have ultimately shown not to be effective in large-scale trials”.

Meanwhile, Dr Katharina Schmack, a psychosis researcher at The Francis Crick Institute in the United Kingdom, said that while the study’s findings were statistically significant, “the absolute numbers are modest” when it comes to schizophrenia risk reduction.

Fifteen years after doxycycline treatment, “instead of about five out of 100 people, now roughly two to three out of 100 would develop schizophrenia,” she said.

Neither Oliver nor Schmack were involved with the study.

Schmack said the findings should serve as the basis for more research into brain development, inflammation, and other biological processes that could affect schizophrenia risk.

“Uncovering clinical associations in studies like this is important because this can direct further biological investigations,” she said.