1 Major depression is a mental illness with seven to nine symptoms, compared to minor depression which has five to six symptoms of depression. Major depression can often manifest over time from minor depression. [source]

2 (Some) people more at risk of major depression include those who have gotten older without a romantic relationship, those who have moved locations, and being a university student. (Survey taken in Australia) [source]

3 Treatment includes Antidepressants, Cognitive Behavioral Therapy, and Interpersonal Therapy. Depression does not discriminate but targets more toward ethnic groups, women, and the elderly. [source]

4 Warning signs or symptoms include insomnia, hopelessness, irritability, loss of interest of once enjoyable activities, suicide ideation, and sometimes psychosis.

5 The science behind major depression is usually due to a chemical imbalance in the brain, e.g a lack of serotonin. The best course of action for a friend to take is to be supportive, check up on their loved ones, and encourage help. [source]