Moncrieff & Timimi ^{Reference Moncrieff and Timimi1} have challenged whether adult attention-deficit hyperactivity disorder (ADHD) exists as a discrete condition. They suggest that it is merely the medicalisiation of ordinary human difficulties and that the diagnosis is being pushed by pharmaceutical companies who then make a tidy profit. They point out the discrepancies between childhood ADHD and adult ADHD and based on this state that adult ADHD is not the same condition. Presumably they subscribe to the view that childhood ADHD suddenly disappears on the child's 18th birthday.

Attention-deficit hyperactivity disorder is a developmental disorder and symptoms change over time. Childhood and adulthood are characterised by differences in lifestyle, pressures, social and moral responsibilities – those of a 40-year-old are clearly very different to those of a child. A child who fails to do his homework will get a telling off or detention, whereas an adult who fails to produce a report to his employer on time may get passed over on promotion or even be made redundant in more extreme cases. The underlying condition is still there, the adult simply learns to cope with or hide it; medication may help them to cope. Drawing on evidence-based medicine, Moncrieff & Timimi report studies where there is no significant difference between stimulant drug and placebo in adult ADHD, yet individual experience has shown dramatic, positive and sustained benefit to the quality of life of individual patients and their ability to function.

The suggestion that adult ADHD is the medicalisation of various common difficulties is unreasonable. The persisting difficulties in ADHD are very much those of inattention and concentration rather than the overt hyperactivity seen in childhood ADHD and it is these very levels of inattention and concentration which have a huge impact on the ability of individuals with ADHD to function in the adult world.

Before the diagnosis and prescription of medication, one of us found it difficult to hold down a job, to hold more than one thought in their head, to remember important facts or to control exuberance in social settings. With the benefit of a diagnosis and stimulant medication, that same individual has built a successful career as a company director, is capable of functioning in noisy offices where he previously floundered and has the ability to focus and to react in a socially appropriate manner. This cannot be pure coincidence.

The fact that ADHD symptoms overlap with a number of other disorders does not negate the existence of the condition. There are symptoms overlapping in a number of psychiatric conditions but this does not lead us to be reductionist with our diagnoses. Indeed, to suggest that those with ADHD have personality disorders is doing them a great disservice. Adults who, after appropriate assessment, are diagnosed with adult ADHD and treated with stimulants have achieved stability in their lives and success in their academic endeavours, employment and relationships which otherwise would never have been possible.