Depression, also known as clinical depression or major depressive disorder, is a common but serious mood disorder that affects how a person thinks, feels, and functions in daily life. It goes well beyond ordinary sadness or a difficult patch, depression involves a persistent low mood or loss of interest lasting most of the day, nearly every day, for at least two weeks, together with changes in sleep, appetite, energy, concentration, or self-worth that interfere with work, relationships, and everyday activities.
Depression is one of the leading causes of disability worldwide and is increasingly recognised in Singapore as a significant public health concern, affecting people across all ages, backgrounds, and walks of life. It is important to understand from the outset that depression is highly treatable. The great majority of people improve substantially with an appropriate combination of psychotherapy, medication, and lifestyle support, but depression, unlike many physical conditions, is often under-recognised and under-treated because its symptoms are mistaken for a personal failing, stress, or simply “not coping,” rather than a medical condition requiring care.
Understanding Depression: What Happens in the Brain and Body
Depression is not simply a matter of willpower or mindset, it is a genuine medical condition involving measurable changes in brain chemistry, brain structure, and the body's stress-response systems.
- Neurotransmitter regulation: Depression is associated with dysregulation of neurotransmitters including serotonin, noradrenaline, and dopamine, which help regulate mood, motivation, sleep, and appetite. This is the basis for how most antidepressant medications work.
- The stress-response system: Chronic stress can overactivate the hypothalamic-pituitary-adrenal (HPA) axis, leading to persistently raised cortisol levels, which in turn affects mood regulation, sleep, and memory.
- Brain structure and connectivity: Imaging studies show that in some people with depression, areas of the brain involved in mood regulation, memory, and decision-making (such as the hippocampus and prefrontal cortex) show altered activity or volume, which may improve with effective treatment.
- Inflammation: Emerging research links chronic low-grade inflammation to depressive symptoms in a subset of patients, an area of active ongoing study.
Types of Depression
Depression is not a single, uniform condition. Recognising which type is present helps guide the most appropriate treatment approach.
Major Depressive Depression (MDD)
The most common and classically recognised form of depression. Persistent low mood or loss of interest for at least two weeks, alongside symptoms such as sleep disturbance, appetite change, fatigue, and difficulty concentrating, severe enough to impair daily functioning.
Persistent Depressive Disorder (PDD)
A chronic, lower-grade depression lasting two years or more. Symptoms are typically milder than MDD at any one point but their persistence can be just as disabling over time. A major depressive episode can also occur on top of PDD (“double depression”).
Seasonal Affective Disorder (SAD)
A pattern of major depressive episodes that recur at a particular time of year, most often during shorter daylight months, and remit at other times. Less common in equatorial regions such as Singapore, but seen in patients with strong seasonal travel patterns or light-sensitive mood cycles.
Perinatal Depression
Depression occurring during pregnancy (antenatal) or within the first year after childbirth (postpartum). Distinct from the brief, mild “baby blues” that many new mothers experience in the first two weeks — perinatal depression is more persistent and severe, and requires specific, prompt clinical attention.
Bipolar Depression
Depressive episodes occurring as part of bipolar disorder, alternating with periods of mania or hypomania. Important to distinguish from unipolar depression, as treatment approaches — particularly antidepressant use — differ significantly.
Symptoms of Depression
Symptoms of depression vary from person to person and can be emotional, cognitive, physical, or behavioural. A diagnosis is generally considered when several of these symptoms are present most of the day, nearly every day, for at least two weeks, and represent a change from the person's usual functioning.
Emotional symptoms
- Persistent sadness, emptiness, or hopelessness
- Loss of interest or pleasure in activities once enjoyed (anhedonia)
- Irritability, frustration, or feeling easily overwhelmed
- Feelings of worthlessness, excessive guilt, or self-blame
- Tearfulness that seems disproportionate to the situation, or an inability to cry at all
Cognitive symptoms
- Difficulty concentrating, making decisions, or remembering things
- Slowed thinking or a sense of mental “fog”
- Persistent negative thoughts about oneself, the future, or the world
- Recurrent thoughts of death, self-harm, or suicide
Physical symptoms
- Fatigue or loss of energy, even after adequate rest
- Sleeping too little or too much, or significantly disrupted sleep
- Appetite and weight change in either direction
- Unexplained aches, headaches, or digestive complaints without a clear physical cause
- Slowed movement and speech, or restlessness and agitation
Behavioural symptoms
- Withdrawing from friends, family, or social activities
- Decline in performance at work or school
- Neglecting personal care or daily responsibilities
- Increased use of alcohol or other substances as a coping mechanism
Risk Factors for Depression
Depression rarely has a single cause. It typically arises from an interaction of biological vulnerability, life circumstances, and psychological factors.
Biological Factors
- Family history: Having a close relative with depression increases risk, though depression can occur without any family history
- Neurochemical and hormonal factors: Including thyroid disorders, hormonal changes around pregnancy, postpartum, and menopause, and premenstrual hormonal shifts
- Chronic physical illness: Conditions such as chronic pain, cardiovascular disease, diabetes, cancer, and neurological conditions substantially raise the risk of depression
- Certain medications: Some medications used for other conditions can contribute to depressive symptoms as a side effect
Psychological and life-circumstance factors
- Significant stressful or traumatic life events — bereavement, job loss, divorce, financial hardship, or major transitions
- Social isolation or lack of a supportive social network
- A history of childhood adversity or trauma
- Co-existing anxiety disorders, which frequently occur alongside depression
- Substance use, which can both contribute to and result from depression
- Personality traits such as a strong tendency toward self-criticism or perfectionism
How Depression is Diagnosed?
There is no single blood test or scan that diagnoses depression. Diagnosis is a clinical process, built on a detailed conversation with the patient, structured assessment, and — where relevant — tests to rule out physical conditions that can mimic or contribute to depressive symptoms.
- Clinical Interview: A detailed conversation covering mood, thoughts, sleep, appetite, energy, concentration, and any thoughts of self-harm, along with personal and family psychiatric history, current stressors, and how symptoms are affecting daily functioning.
- Standardised Screening Tools: Validated questionnaires such as the PHQ-9 (Patient Health Questionnaire) help quantify symptom severity, track response to treatment over time, and screen for suicidal ideation in a structured way.
- Physical Examination and Blood Tests: Used to identify or exclude physical conditions that can present with depressive symptoms — including thyroid dysfunction, anaemia, vitamin B12 or vitamin D deficiency, and certain metabolic conditions — since treating an underlying physical cause can significantly improve mood.
- Assessment for Co-existing Conditions: Depression frequently occurs alongside anxiety disorders, substance use, or (particularly in younger patients presenting with depressive episodes) may represent the depressive phase of bipolar disorder — an important distinction, as it changes the treatment approach.
Living with Depression: Self-Management Alongside Treatment
- Keep to a consistent daily routine, particularly around sleep and wake times, even when motivation is low
- Stay physically active — regular exercise has evidence comparable to some other treatments for mild to moderate depression, and complements formal treatment for more severe cases
- Maintain social connection, even in small ways — isolation tends to reinforce low mood
- Limit alcohol and avoid recreational drug use, both of which can worsen depressive symptoms and interact with medication
- Take medication as prescribed and attend follow-up reviews, even after symptoms start to improve — stopping treatment early is a common cause of relapse
- Build a simple safety plan with your care team if you experience thoughts of self-harm — knowing who to call and what steps to take in advance can be protective during a difficult moment
- Involve trusted family members or friends where appropriate — depression that affects someone close to you is easier to support when others understand what is happening
