Young people are a severely at-risk population, with at least five of the top 10 causes of disability-adjusted life-years directly related to mental health or AOD use disorders . Young people are commonly undertreated [62, 1122], with one study reporting that although more than one-quarter of Australians aged between 16–24 years experienced a 12-month mental disorder, less than 25% accessed health services in a 12-month period .
Comorbidity across disorders is common [42, 269, 1124-1126]. A number of epidemiological studies and government initiatives have identified adolescents and young adults as a group at risk for comorbid AOD and mental health conditions [42, 67, 1127-1131]. The US National Comorbidity Survey reported that the co- occurrence of AOD use disorders and mental illness was highest amongst those aged 15–24 years . In addition, the Australian National Comorbidity Project  identified young people as being at increased risk of poor treatment outcomes and social disadvantage as a result of having comorbid AOD and mental health conditions . A review of community studies of adolescent AOD use, abuse, and dependence revealed that 60% of children and youth with an AOD use disorder had a comorbid diagnosis, with conduct disorder and oppositional defiant disorder the most common, followed by depression .
An Australian study among substance-abusing youth (aged 16–22 years) attending community drug treatment services found high rates of lifetime and current mental health disorders (69% and 50%, respectively) . Almost half the sample (49%) fulfilled criteria for a current mood or anxiety disorder, and this was more pronounced in female participants (61%). Rates of major depression and PTSD were particularly high, and were both associated with significant morbidity. Not only does research suggest that there is an increased prevalence of comorbidity among young people but there is evidence to suggest that adolescents with AOD and co-occurring mood and anxiety disorders also display greater severity of AOD use and associated problems, including increased disability and suicidal behaviour, and reduced academic performance and social abilities [1134-1139].
Adolescence and young adulthood can be a difficult, turbulent time for many people, with issues of change, development, identity formation, experimentation, rebellion, and uncertainty impacting upon an individual’s thoughts, feelings, and behaviour . Thus, it is a vulnerable time for mental health and substance use. It is also often the time in which the first presentations of psychosis and symptoms of depression and anxiety emerge . It should be noted that the presentation of mental illness may be different in young people compared to adults. For example, children who have experienced trauma may not have a sense of reliving the trauma, but rather they may engage in repetitive play activities that re- enact the event. AOD workers who work with children or adolescents should refer to the DSM-5  and be aware of possible variations of symptom expression.
It is important to recognise that AOD and mental health conditions take place in different physical, attitudinal, psychological, and social contexts for young people, and treatment needs to be tailored accordingly [94, 1140]. For instance, treatment should be ‘youth friendly’ and include follow-up for missed appointments, ease of access, prompt screening and assessment, drop-in capability, flexibility, strong links to other relevant agencies to ensure holistic treatment, and interventions that recognise different cognitive capacities and developmental/maturational lags . AOD workers may need to modify the treatment process to avoid client distraction and rebellion (e.g., creating a more active and informal environment) and place special emphasis on engagement (patience and skill is required in addition to the use of appropriate language and questioning and relating to young people on their level).
In regards to confidentiality, most young people would be considered to be ‘mature minors’ by the age of around 14 or 15 years. In this case there is no obligation to provide information to the parents unless other legal and reporting constraints operate, and confidentiality must be respected . In most circumstances, however, it is helpful to involve families (especially parents or carers) and this should be discussed with the young person at the outset of treatment and his/her consent for involvement sought. Parents and carers may require support, education, and empowerment in order to assist with continued care and help prevent client relapse upon discharge [297, 1141].
It may be particularly useful to provide young clients with practical and concrete strategies concerning mental health and AOD use (particularly relapse prevention and urge control). For instance, a behavioural treatment program consisting of stimulus control, urge control, social contracting, problem solving, relationship enhancement, anger management, and communication skills training has been shown to be particularly effective in continued abstinence in adolescents with AOD issues , while cognitive and behavioural therapies have indicated positive outcomes for mental health disorders [1143-1146]. Towers  argues that it is unrealistic to expect many young people to completely cease using all substances and engaging in other risk-taking behaviours (such as driving at high speeds, promiscuity), at least initially. Therefore, it is particularly important to include harm reduction strategies when working with young people.
As young people are fundamentally different from adults in ways that are likely to affect treatment utilisation, adherence, and outcomes [1148-1151], it would be inappropriate to simply replicate adult- focused treatment for young people. Rather, this group requires specialised treatment, focused on meeting developmental and engagement needs. These should include [98, 402]:
- Youth-friendly approach.
- Follow-up for missed appointments.
- Focus on accessibility.
- Prompt screening and assessment.
- ‘Drop-in’ capacity.
- Strong links with other services, and provision of coordinated care (see Chapter B4).
- Treatments that reflect different cognitive capabilities and developmental differences.
E-health interventions, described in Chapter B5, may be particularly useful for this population [98, 1152- 1155]. AOD workers should also be aware that it may take longer to establish rapport and trust within therapy, and adopting a more flexible approach (e.g., consider working outside traditional treatment settings, by talking and playing pool or going to a café), may help build rapport .