Depression: Signs, Symptoms, Causes and Evidence-Based Treatment

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Depression is a common mental health condition that, according to the WHO, affects over 300 million people worldwide. Though often downplayed, depressive states adversely impact mood, thinking, behaviour and physical wellbeing. And while many people associate depression with feeling sad, the condition is far more complex and potentially debilitating. The authors of How to Lift Depression Fast, call it a ‘monstrous, life-destroying experience’ that can significantly impair daily functioning, relationships and quality of life.

This article provides a comprehensive overview of depression, including the most common signs of depression, key symptoms, the relationship between depression and anxiety, recognised causes of depression and evidence-based depression treatment options informed by psychological theory and research.

What Is Depression?

In the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), depression, clinically referred to as major depressive disorder (MDD), is a 'major medical problem that can have a deep and profound impact on a person's safety and well-being.' Depression is characterised by persistent low mood, loss of interest or pleasure and changes in emotional, cognitive and physical functioning lasting for at least two weeks.

Unlike temporary emotional distress, depression affects how a person thinks, feels and behaves over time. It can impact sleep, appetite, motivation, self-esteem and the ability to cope with everyday demands. Depression is recognised by the World Health Organisation as a leading cause of disability worldwide.

Signs and Symptoms of Depression

Understanding the signs of depression and symptoms of depression is essential for early identification and effective intervention. Depression can present differently from person to person, but common symptoms typically fall into four overlapping categories.

Emotional Signs of Depression

• Persistent sadness, emptiness, or low mood

• Feelings of hopelessness or despair

• Emotional numbness or inability to feel joy

• Irritability or increased sensitivity to stress

Cognitive Symptoms of Depression

• Negative self-beliefs and self-criticism

• Difficulty concentrating or making decisions

• Rumination and repetitive negative thinking

• Reduced confidence and self-worth

Physical Symptoms of Depression

• Chronic fatigue or low energy

• Sleep difficulties, including insomnia or excessive sleeping

• Changes in appetite or weight

• Physical aches and pains without a clear medical cause

Behavioural Signs

• Social withdrawal and isolation

• Loss of interest in previously enjoyable activities

• Avoidance of responsibilities

• Reduced productivity or motivation

This long list of signs and symptoms is neatly summed up in How to Lift Depression Fast. ‘If you feel miserable and bad about yourself much of the time, are increasingly preoccupied with negative ideas about your life and the world, don’t feel motivated to do the things you used to enjoy or were good at, find everything an effort and sleep poorly, you have a form of depression.’

If and when you see yourself in this description, and the signs and symptoms persist over time, professional support is strongly recommended.

Depression and Anxiety: A Common Combination

Depression and anxiety frequently walk and in hand, with many individuals experiencing symptoms of both conditions simultaneously. While depression is often associated with low mood and withdrawal, anxiety tends to involve excessive worry, fear and physiological arousal.

The overlap between depression and anxiety can create a cycle of emotional exhaustion, avoidance and self-criticism. Research indicates that shared risk factors – such as chronic stress, trauma and emotional dysregulation – contribute to the development of both conditions.

Effective treatment often requires an integrated approach that addresses both depressive and anxious symptoms rather than treating them in isolation.

Causes of Depression

There is no single explanation for depression. Instead, the condition develops through the interaction of biological, psychological and social factors. The prevailing belief is that depression is a genetic, inherited condition.

Understanding the causes of depression helps reduce stigma and supports more effective treatment planning.

Biological Causes of Depression

• Genetic vulnerability and family history

• Neurochemical imbalances affecting mood regulation

• Hormonal changes, including postnatal depression

• Chronic illness or long-term pain

Psychological Causes of Depression

• Trauma and adverse childhood experiences

• Prolonged stress or emotional overload

• Low self-esteem and harsh self-criticism

• Perfectionism and maladaptive coping patterns

Social and Environmental Causes

• Relationship difficulties or attachment disruptions

• Loneliness and social isolation

• Work-related stress or financial insecurity

• Bereavement or significant life changes

Attachment and Developmental Factors

Attachment theory highlights how early relationships shape emotional regulation and self-worth. Insecure attachment styles are strongly linked to increased vulnerability to depression in adulthood.

In addition, studies show that people who report adverse childhood experiences (ACEs) are more likely to suffer with depression than those who weren’t delt any ACEs.

Types of Depression

Understanding different types of depression can help clarify symptoms and guide treatment.

Common forms include:

• Major depressive disorder (MDD)

• Persistent depressive disorder (dysthymia)

• Postnatal depression

• Seasonal affective disorder (SAD)

• Depression associated with trauma or complex stress

Each type of depression may present differently and benefit from tailored therapeutic approaches.

Psychological Theories of Depression

Several psychological theories explain how depression develops and is maintained.

Cognitive Theory

Beck’s cognitive theory suggests that depression is driven by negative thought patterns about the self, world and future. These beliefs reinforce hopelessness and withdrawal.

Behavioural Theory

Behavioural models propose that depression arises when individuals disengage from rewarding activities, reducing positive reinforcement and deepening low mood.

Psychodynamic Theory

Psychodynamic approaches emphasise unresolved grief, internalised anger and early relational wounds as contributors to depression.

Neurobiological Perspectives

Neuroscience research highlights changes in brain regions involved in mood regulation and stress responses, particularly following chronic stress, trauma or adverse childhood experiences.

Depression Treatment Options

Effective depression treatment options are typically evidence-based and tailored to the individual. What follows is brief description of a range of the most widely used and accepted methods of managing and mitigating depression.

Cognitive Behavioural Therapy (CBT)

CBT focuses on modifying unhelpful thought patterns and increasing behavioural activation. It is widely recommended for depression and anxiety.

Compassion-Focused Therapy (CFT)

CFT is particularly beneficial for individuals experiencing shame and self-criticism, common features of depression.

Psychodynamic and Relational Therapies

These approaches address attachment patterns, emotional conflicts and relational dynamics contributing to depression.

Somatic and Trauma-Informed Therapies

Body-based approaches support nervous system regulation and emotional processing, particularly where depression is linked to trauma.

Medication

Antidepressant medication may be appropriate for moderate to severe depression and is often most effective when combined with therapy.

Depression Recovery and Long-Term Wellbeing

Depression recovery is a process rather than a single outcome. Progress often involves setbacks, learning and gradual change. Protective factors supporting recovery include therapeutic support, social connection, meaningful activity and self-compassion.

Importantly, depression is treatable and many individuals experience significant improvement with the right support.

When to Seek Help for Depression

Professional help should be sought if symptoms of depression persist for more than two weeks, worsen over time, or significantly impact daily life. Early intervention improves outcomes and reduces the likelihood of recurrence.

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Conclusion

Depression is a multifaceted mental health condition influenced by emotional, relational, biological and social factors. By understanding the signs of depression, recognising the interaction between depression and anxiety and addressing the underlying causes of depression, individuals can access effective, evidence-based support.

With appropriate treatment, recovery from depression is achievable. To finish where we started. In the introduction I quoted the authors of How to Lift Depression Fast where they referred to depression as a ‘monstrous, life-destroying experience.’ However, the full quote concludes with the following positive affirmation. ‘Depression can be outwitted, banished, eliminated, torpedoed, [and] totally annihilated – by you.’

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References

Beck, A. T. (1967). Depression: Clinical, Experimental, and Theoretical Aspects. Harper & Row.

Bowlby, J. (1988). A Secure Base. Routledge.

Kessler, R. C., et al. (2015). Epidemiology of depression and anxiety disorders. Annual Review of Clinical Psychology, 11, 1–30.

Lewinsohn, P. M. (1974). A behavioural approach to depression. Journal of Consulting and Clinical Psychology, 42(4), 496–503.

World Health Organization. (2023). Depression Fact Sheet.

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About Dr Laura Allen –

A Chartered Psychologist & Integrative Therapist, Dr Allen specialises in a broad range of therapeutic methods. She is a published author of numerous research papers and Interactive Courses in the field of Psychology. Dr Allen works one-to-one with clients and supervises other practitioners. She is also a proud member of the British Psychological Society assessment team supporting psychologists in training.