Sleeping pills, conceptual artwork. Sleeping pills are prescribed for the treatment of insomnia (the inability to fall asleep or to sleep for long enough). Insomnia has many possible causes, including environmental factors such as noise and light, physical factors such as excess caffeine and lack of exercise and psychological factors such as anxiety, depression and various psychiatric illnesses. Many sleeping drugs promote sleep by reducing the activity of nerve cells within the brain. Long-term use can lead to tolerance and dependence.