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People who take medication for attention deficit hyperactivity disorder (ADHD) for long periods of time and at high doses may be at an increased risk of some cardiovascular diseases, new research suggests.

ADHD is a common neurodevelopmental disorder characterised by having trouble focusing and controlling impulsive behaviour.

In a study of more than 278,000 Swedish ADHD patients aged 6 to 64, researchers found a statistically significant risk for patients taking these medications at doses higher than 1.5 times the daily average.

They also found that each one-year increase in medication use was associated with a 4 per cent increase in the risk of cardiovascular disease.

Long-term use of ADHD medication was associated especially with an increased risk of hypertension and arterial disease.

Methylphenidate, marketed as Ritalin, Concerta, Equasym, Medikinet, or Rubife, was the most commonly dispensed ADHD medication.

It is prescribed to enhance activity in areas of the brain that control attention and impulsive behaviour.

“There is a long list of drugs that have been linked to a comparable increased risk of hypertension when used long-term such as the one found here, so patients should not be alarmed by these findings,” Le Zhang, a postdoc researcher at Karolinska Institutet in Sweden and first author of the study, said in a statement.

“However, in clinical practice, the raised risk should be carefully weighed against the recognised benefits of treatment on a case-by-case basis,” she said.

“Doctors should also regularly follow up the ADHD patients to find signs and symptoms of cardiovascular disease while they’re on medication over the long-term”.

Many people stop using ADHD medication

The findings were published in the journal Jama Psychiatry.

As an observational study, it did not determine a causal link between ADHD medication and cardiovascular disease, but the researchers said the findings showed the importance of determining “potential benefits and risks when making treatment decisions about long-term ADHD medication use”.

Researchers found in a second study, however, that more than half of teenagers, young adults, and adults who start taking ADHD medication stopped doing so within the first year.

The multinational study also found that 35 per cent of children who started taking their ADHD medication stopped taking it in the first year.

“It’s unlikely that so many people discontinue their treatment because their ADHD symptoms have remitted, meaning that the high rate of early discontinuation may be a major barrier to effective treatment,” said Zheng Chang, a senior researcher at Karolinska Institutet who led both studies.

“We haven’t been able to analyse the direct causes in this study, but common reasons for discontinuing ADHD medication are adverse reactions and lack of effect”.

The researchers analysed prescription data from more than 1.2 million patients in Australia, Denmark, Hong Kong, Iceland, the Netherlands, Norway, the UK, Sweden and the USA and found the same pattern in every region.