Major depression is an affective disorder that is referred to in the DSM V, and is the most common psychological disorder.
Affective symptoms that a patient suffering from major depression may experience include distress and sadness. Behavioural symptoms include disturbed sleep patterns, self-destructive behaviour and the avoidance of social company. Cognitive symptoms include feelings of worthlessness or excessive guilt, difficulties concentrating and having a negative attitude towards ones self, the world and the future. However, the feelings of guilt and worthlessness seem to mainly be experiences in Western cultures. Patients also receive far less pleasure from social interaction and show far less initiative than they would otherwise. Somatic symptoms of major depression are fatigue, significant weight loss or gain, loss of appetite, headaches and other pain.
Major depression has a relatively high prevalence compared to other affective disorders. The Nation Comorbidity Study (1994) found that prevalence for lifetime major depression in the USA was 17.1%. Kessler et al (2005) found that, in the USA, there was a prevalence of 13.2% for males and 20.2% for females. Andrade and Caraveo (2003) found that lifetime prevalence of depression varies across cultures, with a prevalence rate of 3% in Japan compared to a prevalence rate of 17% in the USA.
Furthermore, Poongothai et al (2009) conducted a study in the South Indian city of Chennai, based on 25,455 participants who filled out a self-report questionnaire. They found an overall prevalence rate of 15.9%, but also discovered a higher prevalence rate (19.3%) in the low-income group compared to the higher income group (5.9%). They also found that the prevalence of major depression was higher among divorced participants (26.5%) and the widowed (20%), compared to the married participants (15.4%).
Coppen (1967) created the serotonin hypothesis, which suggests that low levels of serotonin, a biological factor, cause depression. Anti-depressants in the form of selective serotonin reuptake inhibitors (SSRI) block the process where serotonin is absorbed, which increased the amount of serotonin in the synaptic gap. According to the serotonin hypothesis, this would lead to an improvement in mood. However, Henninger et al (1996) later performed experiments where they reduced the levels of serotonin in healthy individuals to see if they would develop depressive symptoms. The results did not support the serotonin hypothesis, as they found that the levels of serotonin didn’t influence depression. Furthermore, Kirsch et al. (2002) found that there was publication bias in research on effectiveness of SSRI in depression. They took the results of all studies into SSRI treatment, and found that the placebo effect could be account for 80% of the positive SSRI studies. Of the studies funded by pharmaceutical companies, 57% failed to show a statistically significant difference between anti-depressants and...