See Articles page 57 The use of antipsychotic drugs to treat behaviours such as aggression and self-injury in people with intellectual disability is one of the most controversial issues in mental health. The need to treat these serious problems eff ectively has resulted in high rates of use of antipsychotic drugs in both community and inpatient settings. This trend has continued despite sparse evidence of drug effi cacy for treating aggression in people with intellectual disability and the potential for long-term side-eff ects with both typical and atypical antipsychotics. For these and other reasons, researchers have continued to stress the urgent need for research. Thus the randomised controlled trial in today’s Lancet by Peter Tyrer and colleagues is both timely and important. Tyrer and colleagues measured the eff ects of risperidone, haloperidol, and placebo on the aggressive behaviour of 86 individuals with intellectual disability. Participants were drawn from inpatient and community settings in the UK and Australia. The main fi nding was that although there were decreases in aggression in all three groups after 4 weeks, patients receiving placebo had the most signifi cant reductions. There is much to commend about Tyrer and colleagues’ study. The data are international, and the method was sophisticated and paid careful attention to dose, which is rare. Although the authors note that a larger sample size would have been better, the numbers are impressive in view of the practical, legal, and cultural issues associated with recruiting for such research. However, a point of contention about the conclusions is whether the measures used to assess aggression were suffi ciently sensitive to detect treatment eff ects. In this respect, operational defi nitions of aggression specifi c enough to account for the heterogeneity of the problem are required. This becomes particularly problematic in comparisons of individuals living in community-based settings with those living in institutions, because aggressive behaviours are likely to be more severe in the latter setting. Tyrer and colleagues’ main conclusion is that antipsychotic drugs should no longer be regarded as routine treatment for aggression in people with intellectual disability, although special cases of psychotropic drug therapy might still be warranted in extreme forms of disruptive behaviour or the presence of a comorbid psychiatric condition, for example. We concur, particularly for children, and especially because most aggression in people with intellectually disability has an environmental function, such as escape from demands, attracting carer’s attention, or gaining access to preferred items. However, this opinion is a departure from conventional wisdom. Additionally, there are several factors that might hinder a change in practice. One major issue is that two parallel theoretical models govern modern-day treatments. One approach is biologically oriented and emphasises diff erential diagnosis and drug treatment. The second model is applied behavioural analysis, which rejects symptom complexes in favour of operant explanations of behaviour and treatment. With such an approach, the functions that maintain the behaviour are assessed, and this information is used to create individualised treatment protocols. Much has been published on the treatment of challenging behaviour in people with developmental disabilities. For example, Machalicek and colleagues identifi ed 26 studies in a 10-year span specifi c to school settings. The total published work in all settings since 1970 is thus large. Both approaches do have merit and may benefi t the person with intellectual disability and aggression, yet rarely are the two methods used together. Second, insuffi ciently trained staff makes implementation of applied behavioural analysis diffi cult outside university clinics and hospitals, and in many routine settings this is a strong motivator for the use of drugs.