After anxiety, depression is the most common psychiatric disorder. An estimated 10 percent of the people who see their doctors for what they think is a physical problem are actually experiencing depression. Depression typically begins in the 20s, 30s, or 40s. People born in the latter part of the 20th century seem to have higher rates of depression than those of previous generations, in part because of higher rates of substance abuse. An episode of depression typically lasts for 6 to 9 months, but in 15 to 20 percent of the people, it lasts for 2 years or more.
Episodes generally tend to recur several times over a lifetime.
Causes The causes of depression aren't fully understood. Depression may also arise or worsen without any apparent or significant life stress. Women are twice as likely as men to experience depression, though the reasons aren't entirely clear. Psychologic studies show that women tend to respond to adversity by withdrawing into themselves and blaming themselves. In contrast, men tend to deny adversity and throw themselves into activities.