A doctor of osteopathic medicine (DO) is a licensed physician who may practice medicine, do surgery, and write prescriptions. All areas of medicine are not available in all states. Most DOs do not have the authority to order psychiatric tests or prescribe medications without additional training or licensing. However many perform simple procedures such as giving shots and taking blood samples. The title "doctor" is granted by state boards of osteopathic medicine based on educational requirements, clinical experience, and examination scores. In most states, a medical student must complete three years of undergraduate work before applying for admission to a residency program in osteopathic medicine. During this time, the student may participate in large-group teaching sessions with other doctors-in-training, learn surgical techniques from experienced surgeons, and observe them performing operations. Upon completion of the third year, the student takes a comprehensive exam called the "board certification exam." Only then is it determined whether the student will be allowed to use the title "doctor" after his or her name. Doctors of osteopathic medicine treat patients of all ages, including children, and specialize in several areas of health care. They work closely with physicians who refer patients to them and also see their own share of acute illnesses.