A common ADHD drug affects brain development in children and therefore should be prescribed with caution, doctors have said.
Methylphenidate, known by its brand name Ritalin, alters brain signalling in children with the disorder but not adults, according to a Dutch study.
MRI scans showed the youngsters given the drugs had changes in white matter - which is crucial for sending messages in the body.
The authors are still investigating whether the changes in white matter will have positive or negative outcomes for children.
Methylphenidate (MPH), also sold under the name Concerta, is effective in up to 80 per cent of patients.
However, it has sparked controversy in recent years, with scientists finding the evidence on its pros and cons to be weak after 50 years of use.
Ritalin prescribed to people with ADHD affects brain development in children and therefore should be prescribed with caution, doctors have said
The drug works by changing chemicals in the brain to stimulate areas used for focusing and paying attention.
But until now, little was known about the drug's effect on the development of the brain, including the brain's white matter.
White matter is composed of nerve fibers, called axons, which are covered by a fatty material called myelin.
Ritalin is a medication used to treat attention deficit hyperactivity disorder (ADHD).
It works by changing the amounts of certain natural substances in the brain.
Ritalin is the most commonly known brand name of methylphenidate, which is a drug also sold as Concerta, Inspiral, Addwize and Aptensio.
Methylphenidate belongs to a class of drugs known as stimulants.
It increases the ability to pay attention, stay focused on an activity, and control behaviour problems.
The medication is usually taken two or three times a day orally.
In 2015, a review carried out by Cochranet found that, even after 50 years of use, more research is needed to help doctors decide on the pros and cons of giving ritalin to children.
Doctors said there were signs that children on Ritalin were more likely to experience sleep problems and loss of appetite.
However, the team said that it could not be confident about any of the results.
Mylein protects the fibers and gives white matter its colour, and if it wastes away - normally due to disease - messages can't pass through.
If a person has white matter disease, they will gradually have difficulty with the ability to think, balance and walk.
Researchers at the University of Amsterdam conducted a study of 50 boys and 49 young adult men diagnosed with ADHD.
All patients were medication-naïve, meaning they had never received MPH prior to the study.
Study senior author Dr Liesbeth Reneman said: 'We are the first to study medication-naïve patients in this context.'
She added that this 'is crucial if you want to know how ADHD medications affect the developing brain'.