Major Depressive Disorder (MDD) is a common psychiatric condition characterized by a marked and persistent depressed mood, which may lead to various changes in an individual’s thought patterns, behaviors, and bodily functions. It may present with symptoms such as loss of interest, decreased energy, appetite disturbances, sleep problems, feelings of guilt, and a reduced capacity for emotional responsiveness. This disorder may negatively affect not only the individual’s mood but also their social relationships, as well as their functioning in educational and occupational settings.
Although major depressive disorder may begin at any age, it most commonly emerges during adolescence or early adulthood. Its course may be recurrent in some individuals, while in others it may take on a chronic form. According to the World Health Organization, MDD is among the leading causes of disability worldwide.
Major Depressive Disorder DSM-5 Diagnostic Criteria
The diagnosis of major depressive disorder is established based on the criteria defined in the DSM-5 (Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition). To make a diagnosis, at least five of the following symptoms must be present for a minimum of two weeks, occurring nearly every day and for most of the day:
- Depressed mood (feelings of sadness, emptiness, or hopelessness)
- Markedly diminished interest or pleasure
- Weight loss or gain without dieting, or changes in appetite
- Insomnia or hypersomnia
- Psychomotor agitation or retardation
- Loss of energy or fatigue
- Feelings of worthlessness or excessive guilt
- Difficulty thinking, concentrating, or making decisions
- Recurrent thoughts of death, suicidal ideation, plans, or attempts
These symptoms must cause impairment in social, occupational, or daily functioning and must not be attributable to a medical condition or substance use.
Symptoms of Major Depressive Disorder
The symptoms of MDD may manifest in emotional, cognitive, and physical domains. Individuals may feel persistently sad, empty, or restless. They may lose interest in activities they previously enjoyed and withdraw from social relationships. Physical symptoms such as decreased appetite or overeating, insomnia or excessive sleep, loss of energy, and fatigue may be observed.
At the cognitive level, distractibility, forgetfulness, and difficulty making decisions may occur. In some individuals, feelings of guilt, worthlessness, and inadequacy may intensify, which may pave the way for suicidal thoughts or attempts. Not all individuals experience the same symptoms; therefore, individual differences should be considered in diagnosis.
Causes of Major Depressive Disorder
The development of major depressive disorder may involve the interaction of biological, genetic, psychological, and environmental factors. A single cause may not be identifiable.
- Genetic vulnerability is an important risk factor. Individuals with a first-degree relative who has a history of depression have an increased likelihood of developing MDD. Twin studies indicate that genetic transmission may account for approximately 30–40% of the risk.
- Neurobiological factors include imbalances in serotonergic, dopaminergic, and noradrenergic systems. In particular, reduced serotonin levels are considered a fundamental biochemical basis of depressive symptoms. Additionally, hyperactivity of the hypothalamic–pituitary–adrenal (HPA) axis is associated with depression.
- Psychosocial factors include childhood trauma, parental loss, abuse, unemployment, divorce, and prolonged stress. Adverse experiences at an early age may reduce the capacity to cope with stress.
- Cognitive theories suggest that negative internal dialogues and distorted thinking patterns may contribute to the development of MDD. Beck’s cognitive triad (negative thoughts about the self, the world, and the future) is often cited as an example.
Risk Factors for Major Depressive Disorder
Various risk factors that facilitate the development of major depressive disorder have been identified. These are important in preventive mental health approaches:
- Genetic predisposition
- Female sex (higher prevalence among women)
- History of early-life loss or trauma
- Chronic illnesses (e.g., diabetes, cancer, cardiovascular diseases)
- Substance use (alcohol, stimulants)
- Social isolation, loneliness, lack of support
- Low socioeconomic status and unemployment
- Hormonal changes (e.g., postpartum period, menopause)
The combination of these factors may increase risk; however, no single factor alone definitively determines the disorder.
Diagnosis of Major Depressive Disorder
Diagnosis is established through a detailed clinical interview and a psychiatric evaluation that includes the history of symptoms. Current and past symptoms are assessed in accordance with DSM-5 criteria.
Thyroid disorders, anemia, neurological conditions, and substance-related effects should be ruled out. Therefore, laboratory tests or, when necessary, neuroimaging methods may be employed.
In the differential diagnosis, dysthymic disorder, bipolar depression, and seasonal mood disorders should be considered.
Treatment of Major Depressive Disorder
Major depressive disorder can be largely managed with appropriate treatment approaches. The treatment plan is individualized based on the individual’s life circumstances and the severity and duration of symptoms.
1. Pharmacotherapy
Antidepressants constitute the primary treatment approach. SSRIs, SNRIs, and tricyclic antidepressants are commonly used. Although the effects of medications are typically felt within 2–4 weeks, a longer duration may be required for a full response. Medication selection and dose adjustments are conducted through regular psychiatric follow-up.
2. Psychotherapy
Cognitive Behavioral Therapy (CBT) is the most extensively studied and evidence-based method in MDD. The goals include identifying negative thoughts, restructuring them, and developing functional behaviors.
In addition, interpersonal therapy, psychodynamic therapy, and problem-solving therapy may also be beneficial. In mild to moderate cases, psychotherapy alone may be sufficient.
3. Supportive Approaches
Regular exercise, healthy nutrition, sleep regulation, and social support may reduce symptoms. Mindfulness and relaxation techniques are effective in lowering stress levels.
Family education and support groups facilitate treatment adherence. In severe cases, biological interventions such as electroconvulsive therapy (ECT) or transcranial magnetic stimulation (TMS) may be considered.
The Difference Between Major Depression and Depression
The term “depression” is commonly used in everyday language to describe sadness, low morale, or lack of motivation. This state may be short-lived and related to life events. Major Depressive Disorder, on the other hand, is a clinically defined psychiatric diagnosis based on specific criteria.
In MDD, intense depressed mood lasting at least two weeks, inability to experience pleasure, significant functional impairment, and changes in biological functions are observed. Therefore, not every depressive feeling constitutes Major Depressive Disorder; MDD is one of the most severe and persistent forms of depression.
Effects on Daily Life
Major depressive disorder leads to functional impairment in many areas of an individual’s life. Decreased academic achievement, reduced performance at work, family problems, and social withdrawal are common outcomes.
Low energy and reduced motivation may result in neglect of personal care. Depression frequently co-occurs with anxiety disorders, substance use disorders, and physical illnesses.
Moreover, MDD is a disorder that must be carefully monitored due to the risk of suicide. Research indicates that the majority of individuals who die by suicide have a history of depressive disorders. Therefore, early diagnosis and appropriate treatment are of vital importance.