Clinical Depression: Signs, Causes and Treatment

What is a psychological disorder?

Feeling sad, worried or angry is normal. A psychological (mental) disorder is a pattern that is:

• Strong and unusual for that person and their culture,
• Long-lasting, not just a bad day,
• Distressing to the person, and
• Dysfunctional: it gets in the way of school, work, sleep or friendships.

Disorders are common and treatable. Seeing a doctor for the mind is as sensible as seeing one for the body. Labels must be used with care to avoid stigma (unfair negative judgement).

Diagnosis of clinical depression

Clinical depression (also called major or unipolar depression) is diagnosed by a trained professional using a classification manual: ICD-11 (World Health Organization) or DSM-5 (American Psychiatric Association).

• Core symptoms: persistent low mood and/or loss of interest or pleasure in usual activities.
• Other symptoms: tiredness or low energy, sleeping too much or too little, appetite or weight change, feeling worthless or guilty, poor concentration, hopelessness, thoughts of death.
• Time: most of the day, nearly every day, for at least 2 weeks.
• Severity: mild, moderate or severe, depending on the number and strength of symptoms and how much daily life is affected.

Doctors also rule out other causes, such as a medical illness or grief after a recent loss.

Biological and psychological explanations

Biological explanation

• Neurotransmitters: nerve cells pass messages across tiny gaps called synapses using chemicals. Low levels of serotonin are linked to low mood, poor sleep and appetite changes.
• Genes: depression runs in families. If one identical twin has it, the other is affected more often than in non-identical twins. Genes raise risk but do not guarantee it.

Evaluation: SSRIs that raise serotonin help many people, which supports the theory. But they do not help everyone, and low serotonin may be an effect of depression, not only a cause.

Psychological explanation

• Beck's negative triad: negative views of the self ("I am useless"), the world ("nobody cares") and the future ("it will never get better").
• Faulty thinking: for example overgeneralising ("one bad mark means I fail at everything") and ignoring the positives.
• Stressful life events, such as loss or bullying, can trigger these thoughts.

Evaluation: it explains why CBT works and gives people hope that thinking can change. But it is hard to tell whether negative thinking causes depression or depression causes negative thinking. Most experts use a mix of both explanations.

Treatment: drug therapy and CBT

Drug therapy: antidepressants

The most common are SSRIs (selective serotonin reuptake inhibitors). Normally, serotonin is quickly taken back into the sending cell (reuptake). SSRIs block this, so more serotonin stays in the synapse.

• Strengths: easy to take; help many people with moderate to severe depression.
• Limits: take 2 to 6 weeks to work; side effects such as nausea or sleep problems; depression may return when they stop. They must be prescribed and monitored by a doctor.

Cognitive behavioural therapy (CBT)

A trained therapist helps the person:

1. Spot automatic negative thoughts (often using a thought diary).
2. Test them: "What is the evidence? What would I tell a friend?"
3. Replace them with balanced thoughts.
4. Act: plan small enjoyable or useful activities (behavioural activation).

• Strengths: no physical side effects; skills last, so relapse is lower.
• Limits: needs time, effort and a trained therapist; can be hard when a person has very little energy.

For moderate to severe depression, drugs and CBT together often work best.

Try it

In the free play, change negative thoughts into balanced ones one at a time and watch the mood bar. Then try a mini thought check for yourself: write one worry, the evidence for it, the evidence against it, and a fairer thought. If low feelings last for weeks, talk to a trusted adult or doctor.

Key formulas and definitions

• Disorder = strong + lasting + distressing + dysfunctional
• Depression diagnosis (ICD-11/DSM-5): low mood or loss of interest + other symptoms, ≥ 2 weeks
• Biological: low serotonin at synapses · genes (twin studies)
• Psychological: Beck's negative triad (self, world, future) · faulty thinking
• Treatment: SSRIs block reuptake → more serotonin · CBT: spot → test → replace → act

Worked examples

Common mistakes

• Thinking depression is just feeling sad. Clinical depression lasts at least two weeks and affects daily life.
• Saying antidepressants work in a day. SSRIs usually take 2 to 6 weeks.
• Saying genes decide depression. Genes raise risk; environment and thinking matter too.
• Mixing up the treatments: drugs target brain chemicals; CBT targets thoughts and behaviour.