The prevalence of depression is 5% with the prevalence being between 10% to 20% in adolescence. It is associated with a host of negative outcomes and is comorbid with other mental health problems (e.g. anxiety). It is also a risk factor for the development of substance use and abuse. Depression in youth is a risk factor for the recurrence of depressive disorder across the lifespan.

Mild severity refers to meeting the minimal diagnostic criteria for a depressive disorder. Moderate or severe severity refers to people with clinical symptom levels (1), longer term histories of depressive illness (2), more impairment across several areas of their life (3) or a high level of suicidality (4).

CBT or IPT are efficacious for depressed adolescents with mild to moderate depression. A combination of CBT with medication may be most effective for those with moderate to severe depression. CBT programmes for youth depression typically start with psychoeducation and the theory of intervention and an early application of behavioural techniques. After this, cognitive restructuring is used. CBT manuals differ in supplemental cognitive and behavioural techniques employed (1), relative focus on cognitive change versus behavioural skill building (2), dosing of each technique (3), number of sessions (4), format (5) and level of parental involvement (6). Involvement in negative cognitive style and behavioural mood regulation skills are the mechanisms of CBT effects. Cognitive change appears to mediate the effectiveness of CBT.

Depression is believed to arise from the experience of stressful life events in combination with genetic vulnerability toward mood dysregulation in response to stress, maladaptive behavioural responses to stress and inaccurate, overly negative cognitive interpretations of stressful events.

In the Beckian cognitive theory and the learned helplessness theory, biased, overly negative cognitive processing is thought to arise from stressful early life experience. Individuals learn that the world is an unsafe and unpredictable place and that they are not good At handling stress. These beliefs are activated when faced with stressful circumstances and this interferes with coping and positive mood. Depressogenic thinking is resistant to disconfirmation, partially due to the enduring styles of information processing that promote belief maintenance (e.g. focus on negative information).

A behavioural approach to depression holds that depression results from low levels of positive reinforcement and high levels of punishment and aversive control. This leads to people withdrawing from negative interactions and avoid situations that may produce low mood. This exacerbates the problem of low positive reinforcement. This depressive cycle eventually leads to depression and may be brought about through environmental change or a mismatch between environmental demands and behavioural skills.

Interpersonal psychotherapy (IPT) is a treatment for depression. It conceptualizes depression as occurring within an interpersonal matrix and targets the resolution of psychosocial stresses that coincide with the depressive episode. It does not see environmental factors as the cause of depressive episodes but see them as co-occurring. Nonetheless, alleviating environmental stressors can help in reducing the symptoms of depression. The treatment first categorizes the environmental context in a problem area and then teaches specific strategies for working through each of the problem areas. There is an overall emphasis on restoring meaningful, low-conflict social relationships. There is evidence that IPT impacts interpersonal relationships but it is unclear whether these are mediators.

There are three classes of moderators:

1. Match-to-intervention moderators
   This includes baseline characteristics of youth who are a theoretical ‘match’ for one of the existing evidence-based interventions for depression (e.g. cognitive distortions for CBT).
2. Contextual moderators
   This refers to contextual characteristics that make one person fit a specific treatment (e.g. environmental stressors).
3. Generalizability moderators
   This refers to characteristics that allows to assess whether interventions are robust to clinical complexity and perform well across diverse family characteristics.

The matching hypothesis holds that CBT outperforms control condition and alternate treatment models for youth with matching deficits in cognitive and behavioural processes at baselines.

High levels of cognitive distortions may be an indication for adding on CBT to medication but high cognitive distortions does not improve CBT by itself. Combination treatment is suggested. Perfectionism did not moderate the outcome.

Hopelessness refers to a negative or empty outlook on the future due to the abandonment of expectation of potential contentment or success. This is associated with poor outcomes. CBT may be effective due to large changes in hopelessness. However, lower levels in hopelessness at baseline is associated with a better response to CBT. The moderating effect of hopelessness was not maintained in the long-term.

People with more positive problem-solving skills and mindsets make better use of CBT as a tool to reduce suicidality. Coping style is a moderator of the effects of CBT. People with more positive coping skills perform better, meaning that CBT is most effective with youth who already had strengths in coping to build upon.

People’s use of pleasant activities at baseline is not related to CBT responses. The relative benefit of CBT does not depend on perceived social support and neither did parent-child conflict, family conflict or family cohesion. In high-conflict households, another treatment is superior to CBT for males but not for females. Females in a high-conflict household have a generally uniform and positive response to CBT. However, females in a low-conflict household have a worse response to CBT. Marital conflict moderates the response to intervention for depression among highly oppositional adolescents. CBT appears to be effective under conditions of low marital discord.

People who reported good family function were more likely to benefit from combination treatment. CBT is superior for people with low or moderate levels of stressful life events and substance use but not for those with high levels. CBT is superior for youth without a history of sexual abuse but this is not the case for those with a history of sexual abuse. Youth with a history of sexual abuse had poor outcomes in CBT alone. Youth without a trauma history had superior outcomes with combination treatment. Trauma history moderated response to flatten out the superior effects of combination therapy for youth with history of sexual abuse and reverse the relative benefits of combination and monotherapy for youth with physical abuse. Youth with a history of physical abuse had a superior response to medication monotherapy over combination.

Combination treatment was most efficacious for people with mild to moderate depression. However, for severe depression, there was no difference with monotherapy of medication.

The presence of anxiety disorder predicts worse outcomes over time across treatment. However, anxious youth might be relatively better when it comes to CBT compared to other treatments though this outcome may not hold over time. Substance use predicts poor treatment outcome overall but does not demonstrate a moderating effect. However, they may have better outcomes with CBT when they score low to medium on substance use compared to when they score high. Youth without ADHD who receive combination treatment had a greater improvement on depression symptoms compared to youth with ADHD. Depressed adolescents with comorbid ADHD scored higher on combination therapy compared to medication monotherapy.

Age has not been found to moderate response to treatment. Verbal intelligence did not moderate outcomes. Gender did not moderate treatment outcome. Income is a moderator. In lower income families, there is an equal effectiveness of combination treatment and medication and both are better compared to CBT alone or placebo. In the high-income group, the treatments are better than placebo but show equal effectiveness.

There are stronger effects for combined treatment for Caucasian adolescents. CBT is superior compared to control for Caucasian adolescents with depression and disruptive behaviour.

IPT is especially effective if adolescents have significant interpersonal problems. Mother-child conflict and problems with peer relationships also seems to make this treatment more effective. Quality of dating relationships does not moderate the outcome. Achievement orientation moderates response to IPT and control but not to BCT. This means that people with higher levels of achievement orientation have lower levels of depressive symptoms over time.

IPT is superior to regular counselling for youth with the most severe depression and functioning problems. There is no difference between IPT and regular counselling on less severe cases. IPT may be superior compared to other treatments for depressed adolescents with anxiety disorders.