Chronic circadian rhythm disorders, the most common of which is delayed sleep phase disorder, may be managed by specifically-timed bright light therapy, usually in the morning, darkness therapy in the hours before bedtime, and timed oral administration of the hormone melatonin. Chronotherapy has also been prescribed for circadian rhythm disorders, though results are generally short-lived. Stimulants may also be prescribed. When these therapies are unsuccessful, counseling may be indicated to help a person adapt to and live with the condition. People with these disorders who have chosen a lifestyle in conformity with their sleeping schedules have no need of treatment, though they may need the diagnosis in order to avoid having to meet for appointments or meetings during their sleep time.