Major depressive disorder (MDD) is one of the most prevalent mental disorders among adolescents. The prevalence in adolescence is 15% to 20%. Early onset is marked by a recurrent course, psychiatric comorbidity and a range of negative outcomes (e.g. poor academic achievement). Adolescent MDD has a mean duration of six months but longer episodes are associated with earlier onset or suicide ideation.

The experience of MDD impacts almost all domains of functioning. People who have had a depression continued to experience differences on domains of functioning compared to never-depressed peers. There likely is not a single maintaining or causal factor for depression. Comorbidity is very common at almost 50% with anxiety disorders (1), substance use disorder (2) and conduct disorder (3) being most common. Comorbidity is higher in adolescence than in adulthood.

The cognitive vulnerability model states that individuals at risk for depression selectively focus and have better memory recall for negative rather than positive stimuli. One important goal of cognitive-behavioural treatment (CBT) is to help people become aware of pessimistic thoughts (1), depressotypic beliefs (2) and causal attributions of self-blame (3). After recognition, these cognitions can be changed for more realistic ones.

Behavioural theories of depression emphasize the role of maladaptive actions in the onset and maintenance of depression. It holds that depressive symptoms develop and persist as the result of decreased environmental reward (1), reductions in positively reinforced behaviours (2) and reinforcement of depressive behaviours (3). The goal of behaviour based treatment is to increase engagement in activities that are personally reinforcing.

CBT combines cognitive and behavioural strategies. It includes focus on specific and current actions and cognitions (1), structured sessions (2), repeated skills practice (3), the use of rewards and contracts (4), homework assignments (5) and a relatively small number of sessions (6). CBT tries to teach adolescents a variety of coping strategies that will allow them to counteract the diverse factors that contribute to their depression and deal more effectively with new problems.

The adolescent coping with depression course (CWD-A) is a group-based CBT intervention for depression. It consists of 16 two-hour sessions over 8 weeks. It includes eight components:

1. Treatment begins with explaining the treatment rationale.
2. Participants monitor their mood daily throughout treatment to provide baseline data and identify mood changes.
3. Pleasant activities are increased as a form of behavioural activation and this includes baselining current activity level (1), setting realistic goals to increase the frequency or variety (2), develop a change plan (3) and include self-reinforcing goal achievement (4).
4. Participants receive social skills training (e.g. practice in basic conversation techniques).
5. Participants receive relaxation training with progressive muscle relaxation and deep-breathing techniques.
6. Treatment attempts to reduce depressogenic cognitions by identifying, challenging and changing negative thoughts and irrational beliefs and change them for more positive beliefs.
7. Participants are taught improved communication (e.g. active listening) and problem solving.
8. The treatment concludes with relapse prevention (i.e. skills integration; anticipation of future problems).

A parallel parent group exists which has the goals of informing parents of the CBT materials the children are learning to encourage them to support and reinforce their new skills and teach parents the communication and problem-solving skills that are being taught to their child. There are two joint sessions with the parents and the children in week seven.

A first trial indicated no difference between the parent condition and the regular CBT programme. It was effective for 46% after treatment and 83% after six months. The gains were maintained and recurrence was very low. Boosters (i.e. another meeting after a couple of months) were not effective to prevent recurrence but it was effective for people who were still depressed. Boosters may need to be given semi-frequently to those who have not recovered after treatment.

Depressed adolescents with substance use disorders had a slower time to depression recovery. People with comorbid disruptive behaviour disorders were more likely to experience recurrence. CWD-A appears to be effective for adolescents with significant comorbidity but does not impact the comorbid disorder.

When an adolescent has MDD, providing them with CWD-A first also leads to greater substance use reductions. When the adolescent does not meet the requirements for MDD, this does not occur. There is not a specific treatment sequence that leads to better outcomes. There was lower engagement in the second treatment.

People receiving CWD-A in a group setting in usual care did not incrementally benefit compared to usual care. However, these people also had a depressed parent and this may stagger results.

One study found that CBT and anti-depressant combination was more effective than a placebo but not CBT by itself. Combined treatment was also superior to both monotherapies. It may be that the CBT was too intensive or too complex in this study.

There may be four options for CBT to have a strong clinical impact:

1. Focus on prevention rather than treatment
   It may be effective as pharmacological interventions are not recommended for prevention and most prevention programmes are group-based which allows for delivering CBT.
2. Use CBT to augment medication treatment
   Anti-depressants may lead to symptom response or remission but CBT may be used to build on this positive response and reduce recurrence.
3. Embed CBT within standard medical care
   This may be cost-effective and practical and reduce depression rates.
4. Use eMental health approaches
   By making CBT internet-based, it may be able to target those that do not actively seek treatment.

Potential moderators include depression severity (1), patient preference (2) and parental depression (3). CBT may need to use a capitalization rather than compensation model. It also needs to be clarified when and how parents should be involved. It is also important to assess whether group-based treatment is more effective in overlearning CBT skills. Next, the mechanisms of change need to be assessed. Lastly, it is also important to know how CBT can be delivered through the internet.