Experts found that children treated with methylphenidate before the age of 13 were less likely to go on to develop conditions such as schizophrenia in adulthood.
The findings challenge long-standing concerns that stimulant medications may increase the risk of psychosis, experts say.
Reassuring findings
ADHD is a common neurodevelopmental condition that affects attention, behaviour and impulse control, and is often diagnosed in childhood. While most young people do not develop severe mental illness, a small proportion go on to experience psychotic disorders in later life.
To better understand whether medication plays a role in this risk, researchers from the University of Edinburgh and University College Dublin analysed health data from nearly 700,000 people born in Finland, including around 4,000 individuals diagnosed with ADHD.
The team found no evidence that treatment with methylphenidate increased the likelihood of developing psychosis. Instead, children who received the medication at a younger age showed a reduced risk compared with those who were not treated early.
Early treatment
Methylphenidate is the most commonly prescribed medication for ADHD and is widely used to manage symptoms such as inattention and hyperactivity.
Researchers say the findings suggest the drug may have benefits beyond symptom control, potentially influencing longer-term brain development in ways that reduce vulnerability to severe mental illness.
However, the apparent protective effect was only seen in those treated during childhood. The same benefit was not observed in individuals who began treatment during adolescence or adulthood.
Further research
The study comes at a time when ADHD diagnoses are rising rapidly worldwide, particularly among adults, prompting increased debate about the long-term safety of stimulant medications.
Researchers say the findings highlight the importance of early diagnosis and age-appropriate treatment, as well as the need for further research into how these medications affect the brain at different stages of development.
The study was funded by the St John of God Research Foundation.