Unlike most of the disorders discussed in this book, attention deficit hyperactivity disorder (ADHD) is, in childhood at least, more common in males than in females. This is both an advantage and disadvantage when it comes to writing a chapter such as this. Whilst most of the research has been conducted in males, meaning that there is a lot to say, those studies that have included females with ADHD or attempted to contrast males and females have often been underpowered and delivered inconclusive findings. Also many of these studies have failed to include healthy comparison groups, making it difficult to know what is specific to ADHD and which differences are simply reflecting more general differences between the sexes.

As you work through the chapters in this book it will become very clear that since the beginning of the ‘decade of the brain’ in 1990 we have made considerable progress in understanding how the brain works and the way that it develops across the lifespan. We have also made significant progress in understanding the genetic and environmental factors that contribute to the development of mental health problems. We still, however, struggle to develop new and innovative treatments and therapies and in our understanding of what works for whom in what circumstances – more recently labelled precision or personalized medicine. There are, of course, many factors that contribute to this lack of concrete progress. Psychiatric disorders are complex and heterogeneous across several levels of analysis: phenotypically, with co-morbidity being the rule rather than the exception; aetiologically, with a complex genetic architecture based on different types of genetic variants and gene–environment interplay and diverse brain alterations. Also, as there is no stable, agreed-upon, and biologically valid construct for any of the recognized psychiatric disorders, the current taxonomy provides an unclear basis for informed biological research. Attempts to define biologically homogeneous subtypes (‘biotypes’) or pathophysiological dimensions of psychiatric disorders are under way but have yet to deliver (Feczko et al., 2019). From another angle, enormous scientific challenges are still presented by the complexity of the brain’s architecture and physiology, our far from complete understanding of how these change across development, and the relationships between structure and function and between cognition and behaviour/symptoms. These continue to present enormous scientific challenges.

Whilst the use of medication to treat psychiatric problems is less common in children and adolescents than in adults, rates of prescription are increasing for these groups. Notwithstanding a significant increase in the number and quality of clinical trials of psychotropic medications in children and adolescents there are continuing concerns that increases in rates of prescribing still outstrip the evidence base. For example, the prescribing of antipsychotics for children 7–12 years of age in primary care within the UK almost tripled between 1992 and 2005, with the prescribing of ‘atypical antipsychotics’ increasing 60-fold from 1994 to 2005 (Rani et al., 2008).

Historically, paediatric pharmacology in general and paediatric psychopharmacology in particular have received much less research interest and funding than their adult counterparts. As a consequence, relatively few drugs are licensed for use in child and adolescent populations.

One of the greatest obstacles to evidence-based clinical practice is the time taken to translate research findings into treatment recommendations that are effective and usable in a general out-patient setting. Unfortunately, there are also several clear examples of changes in clinical practice outstripping the available evidence. In this chapter and the next, we describe some of the recent advances and current controversies in child and adolescent psychopharmacology. With the exception of attentiondeficit hyperactivity disorder (ADHD) in this chapter, they are organised by disorder rather than drug class. The section on ADHD is organised by class of drug as this best reflects the ways in which clinical decisions are made about individual patients.

Attention-deficit hyperactivity disorder

There has been more research into the use of medication for the treatment of ADHD than any other area of child and adolescent psychopharmacology, and most clinicians are now comfortable with the idea of using medications as a part of their treatment of ADHD. There have, however, been key advances in knowledge and several new treatment options introduced over the past few years. In addition, more basic science studies have helped clarify the relationship between the pharmacokinetics and misuse potential of stimulant medications (Volkow et al, 1995) and raised interesting questions about the relationship between core ADHD symptoms and cognition (Coghill et al, 2007). Clinical studies have started to address the similarities and differences between different medications as well as their effect on non-core aspects of functioning and quality of life (Coghill, 2010). In view of the quantity of trial data and the fact that most clinicians are used to working with these drugs, we focus here on newer medications and current controversies.

Evidence-based treatment and the MTA study

The end of 1999 saw the publication of the primary findings from the Multimodal Treatment of Attention Deficit Hyperactivity Disorder (MTA) multisite study, which was funded by the US National Institute of Mental Health. These findings, and the ensuing commentaries and criticisms of the study, marked a milestone in child and adolescent psychiatry research.