An antibiotic commonly prescribed for acne management has been linked to a reduced chance of developing schizophrenia.
In a new study led by researchers at the University of Edinburgh, adolescents using mental health services who took doxycycline were less likely to be diagnosed with schizophrenia in adulthood, compared to individuals who took other antibiotic types.
While the tentative findings cannot prove that doxycycline prevents schizophrenia, the researchers argue that the drug's effects on immune responses, inflammation, and programmed cell death may help prevent neurological changes responsible for the condition.
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"The observational data used in this study cannot provide definitive evidence of a causal relationship between doxycycline treatment and reduced schizophrenia risk, meaning that further research will be necessary," the authors conclude.
"However, these findings raise the tentative but exciting possibility that doxycycline treatment may reduce schizophrenia risk in adolescent psychiatric patients and point to important new therapeutic opportunities for future mental illness prevention research."
Schizophrenia is a serious mental health condition that affects 23 million people worldwide, most of whom are diagnosed in their late teens or twenties.
The condition can come on suddenly, causing psychosis. Common symptoms include persistent delusions, hallucinations, disorganized thinking, extreme agitation, or social withdrawal.
According to the World Health Organization (WHO), more than two out of three people with psychosis do not receive specialist mental health care.
Doxycycline is a broad-spectrum antibiotic often prescribed to adolescents for acne vulgaris, and some recent studies suggest it may have neuroprotective effects, as it can cross the blood-brain barrier.
In 2024, a Danish study found that this brain-penetrating antibiotic was linked to a significantly lower incidence rate of receiving a disability pension among schizophrenia patients, which is indicative of how the condition may impact their lives.
To find out more, child and adolescent psychiatrist Ian Kelleher of the University of Edinburgh led an international team in an analysis of data from more than 56,000 people born in Finland between 1987 and 1997, who had sought out mental health services as adolescents and who had also been prescribed antibiotics in their youth.
Those treated with doxycycline had a 30 to 35 percent lower risk of developing schizophrenia within the next decade compared to peers who received other antibiotics, dropping from a 2.1 percent chance among those who took other antibiotics to a 1.4 percent chance among those who took doxycycline.
Perhaps doxycycline is ridding the body and brain of an infectious threat, which may play a role in the development of schizophrenia. Or maybe the antibiotic has a direct impact on brain inflammation and brain wiring.
Studies using other antibiotics provide some clues. A 2019 study using stem cells derived from individuals with schizophrenia and healthy volunteers found that minocycline reduces the excessive pruning of synaptic connections that has been implicated in schizophrenia.
Minocycline and doxycycline are both tetracycline antibiotics, so there may be some similarities in how they work.
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Using health data from Finland, Kelleher and his colleagues found that nearly half of all psychotic disorders diagnosed in the population occurred
in individuals who had attended psychiatric services as adolescents.
They argue that this may be an opportune time to intervene, using medications such as doxycycline to reduce the chances of their condition progressing.
"As many as half of the people who develop schizophrenia had previously attended child and adolescent mental health services for other mental health problems," says Kelleher.
"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."
The study was published in the American Journal of Psychiatry.