It often also has serious cognitive effects on people.
Weak short-time memory, loss of ability to focus on anything that before depression struck would be interesting and/or rewarding for the person concerned.
The brain is bombarded with self-defeating thoughts, bad memories and leaves no energy for analytic problem solving or much of anything really.
These deficits can lead to a loss of quality of life, ability to function at work and in ones social life.
Ketamine has shown some potential in being an alternative in how to treat depression naturally but much research remains.