A broader definition of attention-deficit/hyperactivity disorder (ADHD) has contributed to a steep rise in diagnosis and prescriptions, particularly among children, warn experts on bmj.com.
Rae Thomas, a senior researcher at Bond University in Australia, and colleagues say that this may mean "unnecessary and possibly harmful medical treatment" for some individuals, with others estimating drug costs of up to $500m in the US alone.
They argue that reducing the threshold for diagnosing ADHD "devalues the diagnosis in those with serious problems" and call for "a conservative stepped diagnostic approach" to help reduce the risk of overdiagnosis.
To be diagnosed with ADHD, a child, adolescent, or adult should meet clear diagnostic criteria outlined in the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM-5) - used around the world to classify mental disorders - or International Classification of Diseases (ICD-10).
But the authors point out that definitions of ADHD have been broadened in successive editions of DSM - and the more restrictive diagnostic criteria of ICD 10 result in smaller prevalence rates than ADHD diagnosed using the DSM criteria.
Most children are diagnosed with mild or moderate ADHD.
It is likely that clinicians are better at detecting and diagnosing ADHD - but it is also thought that some of the rise reflects overdiagnosis or misdiagnosis, they write.
Prescribing rates for commonly used drugs for children diagnosed with ADHD have also increased, they add. Australian data show a 73% increase for ADHD medication between 2000 and 2011, while in the United Kingdom prescriptions increased twofold for children and adolescentsand fourfold in adults between 2003 and 2008.
Prescribing of methylphenidates and amphetamines in the US increased steadily between 1996 and 2008, with the greatest increase in adolescents aged 13-18 years. And in the Netherlands, prevalence and prescribing rates for children who had ADHD diagnosed doubled between 2003 and 2007.
Despite this, there is very little data on the long term benefits of treatment, say the authors. These medications can cause adverse reactions such as weight loss, liver toxicity, and suicidal thoughts, and in the short term may suppress pubertal growth.
A diagnostic label also carries a stigma, they add. Children labelled as having ADHD are perceived as lazier and less clever by peers, and teachers and parents have low academic expectations of them potentially creating a self fulfilling prophecy.
Severe cases of ADHD are obvious, but in mild and moderate cases - which constitute the bulk of all ADHD diagnoses - subjective opinions of clinicians differ, say the authors.
For these cases, they propose a stepped diagnostic approach "to reduce unnecessary diagnoses without risking undertreatment of those who really need psychiatric help."
They conclude: "Despite extensive research into factors contributing to ADHD aetiology, we are no closer to understanding the cause or causes of this disorder. The broadening of the diagnostic criteria in DSM-5 is likely to increase what is already a significant concern about overdiagnosis. It risks resulting in a diagnosis of ADHD being regarded with scepticism to the harm of those with severe problems who unquestionably need sensitive, skilled specialist help and support."