I want to begin this lecture by reintroducing the conceptual framework for this series of lectures. In terms of considering mental disorders, we are considering some of the most common adolescent health problems that cause substantial disability during these years. If we consider the range of adolescent mental disorders, think through the groups shown here. Affective disorders include depression and bipolar disorder, sometimes known as manic depression. Anxiety disorders include low-level or generalised anxiety, which is continuous, panic attacks that are episodic, or anxiety that occurs in relation to specific circumstances. Examples of some of these more specific anxiety syndromes includes social anxiety where a young person experiences intense anxiety when asked to perform in front of other people. This might be something like giving a talk in front of a class group. Other examples of specific anxiety syndromes would be agoraphobia where an individual has a fear of being outside alone. Anxiety disorders such as these, and depression, commonly occur together. Adolescence is a time when an individual develops a clear identity. This may be one of the reasons why problems of body image, such as anorexia nervosa, or bulimia nervosa, commonly arise at this time. Other behavioural problems such as deliberate self harm, typically in the form of cutting or taking repeat overdoses relate more specifically to difficulties with emotion and emotional control. There are a range of substance use disorders that also emerge during adolescence. Nicotine dependence can arise for some adolescents soon after the commencement of tobacco use. Alcohol and other illicit substance use disorders also commonly emerge during the adolescent and young adult years, and tend to peak in prevalence around the mid-20s. The last group of disorders that fairly typically arise during the teens and early twenties is psychotic disorders. Of which the commonest is probably schizophrenia. These are often more severe disorders, and although less common than depression and anxiety, commonly have a devastating affect on the life course and adjustment of the individual. If we look at the age of onset with these disorders, the great majority have an onset between the ages of 8 and 25 years. Attention deficit hyperactivity disorder, or ADHD, conduct disorder, and anxiety disorders tend to have an earlier onset than depressional substance use disorders. But the overall message remains that the great majority of mental disorders have their onset before 25, and most of these have an onset before the age of 14. The next graph illustrates the points in which these disorders have their maximal impact in terms of health related disability. The metric that we're using here is the DALY. I've mentioned the DALY in a previous lecture. It's a widely used measure of disease burden that takes into account years of life lost due to premature death and years of life lived with disability. And if we look at the age group, 10 through the 24, it's clear that many mental disorders peak in terms of their contribution to burden of disease in this window. Depression and anxiety make the largest contribution to burden of disease across the life course for the peak in the young adult years. Alcohol use and other substance use disorders also have a contribution, which is greatest during the young adult years. This next graph illustrates the growing contribution of mental disorders to disease burden across the years from birth through to 24. The overall burden of disease increases progressively across each five year band. Having said this, the type of disorder contributing to disease burden changes markedly across the years from childhood to young adulthood. In younger children, conduct disorder is a major contributor. Violence, depression, and anxiety disorders become major contributors, and by young adulthood substance use and alcohol abuse disorders are major contributors. This graph provides an idea of the contribution of mental disorders to disease burden relative to other health problems across the years from 10 through to 24. Three of the leading ten causes of disease burden relate to mental health. Whichever way on looks at mental and behavioural problems across the adolescent and young adult years, they are major contributors to disease burden in this age group. And if we thought these problems were still largely problems of high income countries we need to think again. This slide shows the prevalence of DSM disorders in females aged 18 through to 24. These data were taken from the World Mental Health Survey, the largest and most comprehensive survey of global mental health in adults. The gold colours represent high income countries and the blue low and middle income countries. Although a number of high income countries do have higher prevalence rates, the picture suggests high rates of mental disorder can also occur in young women in low and middle income countries. This bubble diagram shows the proportion to of DALYs to the mental disorders in children and adolescents in high income countries. And you can see what a large proportion of the burden of disease mental disorders contribute to. In contrast, in lower and middle income countries, the proportion of disease burden that mental disorders contribute is lower, in large part because of other contributors, such as infectious disease, nutritional problems, and neonatal problems. In this last slide, we are looking specifically at 10 to 24 year olds. The countries of Western Europe are those where mental disorders make the greatest relative contribution to disease burden. In contrast, in Sub-Saharan Africa the contribution is proportionately lower. In this lecture I hope I've illustrated the very substantial contribution that mental disorders make to health during the adolescent years. Although the relative contribution is much greater in high income countries, adolescent mental disorders are a global problem.