It is amazing how seeing information in print, or hearing from an authority, can change your perspective. Learning the facts helps you help your friend, and also shows that you care enough to take some trouble. Therapy and medication are the solution. I would advise anyone seeking treatment to be open to both. Therapy can help us resolve the problems that led to the depression and help us learn how to prevent future episodes.
Research shows that medication and therapy together are more effective than either by itself.
Some people do recover on either medication or psychotherapy alone, but I'd really recommend being open to both. After recovery, sometimes a maintenance dose of medication or a periodic check-in with a therapist is helpful. Manic depression, or bipolar disorder, seems to be a different sort of animal. It strikes one percent of the population. It is more genetically linked than other forms of depression and it responds uniquely to a single medication - lithium.