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.
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.
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’.
Patients received either MPH or a placebo for 16 weeks. Before and one week after treatment, the participants had an MRI scan.
The MRI measured fractional anisotropy (FA), which is used to assess the quality and composition of white matter.
Boys had ‘increased white matter FA’ after four months of treatment with MPH, which indicates MPH affects white matter maturation, the authors said.
But they are not sure whether high FA has good or bad implications and whether they are reversible.
No changes were seen in the adults, according to the findings published in the journal Radiology.
Commenting on the study, Professor David Nutt, Faculty of Medicine, Department of Brain Sciences at Imperial College London, said: ‘This is an interesting and well conducted study with placebo controls.
‘The impact of methylphenidate to increase FA (fractional anisotropy) maybe explains why methylphenidate is an effective treatment for ADHD.
‘There is evidence from other psychiatric disorders that increased FA is associated with clinical improvements. Why the effect should be seen in the adolescence, but not adult brain is unclear, but may reflect greater opportunity for change in the younger brain.’
Dr Reneman and colleagues are studying the long-term implications of MPH, a vital area of research considering many ADHD patients use the drugs for years.
In the meantime, the researchers want to see tighter regulations for prescribing ADHD medications.
Dr Reneman said: ‘What our data already underscore is the use of ADHD medications in children must be carefully considered until more is known about the long-term consequences of prescribing methylphenidate at a young age.
‘The drug should only be prescribed to children who actually have ADHD and are significantly affected by it.’
Around five per cent of children in the UK and US are believed to have ADHD.
Approximately 5.2 per cent of American children between the ages of 2 and 17 take ADHD medication, according to the Center for Disease Control and Prevention.
Some experts believe ADHD drugs are doled out too easily in the UK.
Just one in ten children with the condition are prescribed drugs, experts from Oxford University, King’s College London found in October 2018.
However, in the same month, researchers at University College London said pupils given medication for ADHD are often just younger – and more hyperactive – than peers in their year.
Dr Punit Shah, psychology lecturer, University of Bath, said: ‘Notwithstanding limitations of the study, I agree with the authors sentiments about the (over) prescribing of medication for ADHD and related neurodevelopmental conditions.
‘This is a bigger issue in the US than the UK, but there is growing use of these pharmacological agents in children and young adults across the world.’
Symptoms of ADHD include being disruptive, fidgety, interrupting others and showing signs of emotional upset.
MPH is also sold on the black market to students at high school and university because it can help healthy people focus better, too.