Doctor of Osteopathic Medicine (DO or D.O.) is a professional doctoral degree for physicians and surgeons offered by medical schools in the United States. A DO graduate may become licensed as an osteopathic physician, having equivalent rights, privileges, and responsibilities as a physician who has earned the Doctor of Medicine (MD) degree.^[1] DO physicians are licensed to practice the full scope of medicine and surgery in 65 countries,^[2] and in all 50 US states. They constitute 11% of all US physicians. As of 2018, there were more than 145,000 osteopathic medical physicians and osteopathic medical students in the United States.^[3]

DO degrees are offered in the United States at 35 medical schools, at 55 locations compared to MD degrees offered at 141 schools.^[4][5] Since 2007, total DO student enrollment has been increasing yearly. In 2015, more than 20% of all medical school enrollment in the US comprised DO students.^[6][7] The curricula at osteopathic medical schools are similar to those at MD-granting medical schools, which focus the first two years on the biomedical and clinical sciences, then two years on core clinical training in the clinical specialties.^[8]

Upon completing medical school, a DO graduate may enter an internship or residency training program, which may be followed by fellowship training.^[8] Some DO graduates attend the same graduate medical education programs as their MD counterparts,^[9] and then take MD specialty board exams,^[10] while other DO graduates enter osteopathic programs,^[11][12] and take DO specialty board examinations.^[13]

One notable difference between DO and MD training is that DO training adds 300–500 hours studying techniques for hands-on manipulation of the human musculoskeletal system,^[1][14] a system shared (in general but not all particulars) with chiropractic medicine.

The practice of osteopathy began in the United States in 1874. The term "osteopathy" was coined by physician and surgeon^[15][16] Andrew Taylor Still, who named his new discipline of medicine "osteopathy", reasoning that "the bone, osteon, was the starting point from which [he] was to ascertain the cause of pathological conditions".^[17] Still founded the American School of Osteopathy (now A.T. Still University of the Health Sciences) in Kirksville, Missouri, for the teaching of osteopathy on May 10, 1892. While the state of Missouri granted the right to award the MD degree,^[18] he remained dissatisfied with the limitations of conventional medicine and instead chose to retain the distinction of the DO degree.^[19] In 1898 the American Institute of Osteopathy started the Journal of Osteopathy and by that time four states recognized the profession.^[20]

The osteopathic medical profession has evolved into two branches: non-physician manual medicine osteopaths, who were educated and trained outside the United States; and US-trained osteopathic physicians, who conduct a full scope of medical practice. The regulation of non-physician manual medicine osteopaths varies greatly between jurisdictions. In the United States, osteopathic physicians holding the DO degree have attained the same rights, privileges, and responsibilities as physicians with a Doctor of Medicine (MD) degree.^[1] Osteopathic physicians and non-physician osteopaths are so distinct that in practice they function as separate professions.

As originally conceived by Andrew Still, the letters "DO" stood for "Diplomate in Osteopathy" and the title conferred by the degree was "Doctor of Osteopathy".^[21] Subsequently, the degree also came to be entitled "Doctor of Osteopathic Medicine".^[22] Since the late 20th century, the AOA has preferred that this title be used exclusively.^[23] Its members resolved at a 1960 conference:

A minority of DOs continue to use the old terms, and the American Academy of Osteopathy retains the old usage in its name.^[25]

In 2018, there were 114,425 osteopathic medical doctors in the United States and 145,343 total DOs and osteopathic medical students. The proportion of females in the profession has steadily increased since the 1980s.^[26] In 1985, about 10 percent of DO physicians were female, compared with 41 percent in 2018.^[3] Between 2008 and 2012, 49 percent of new DO graduates were females.^[26]

During the 2011-12 academic year, the osteopathic medical student body consisted of: 69 percent white/non-Hispanic, 19 percent Asian or Pacific Islander, 3.5 percent Hispanic, 3 percent African-American, and 0.5 percent Native American or Alaskan.^[26] The remainder were listed as "other or not entered".

The five-year change in osteopathic medical student enrollment by ethnicity has increased by 19 percent for white/non-Hispanic students, 36 percent for Asian-American students, 24 percent for Black/African American students and 60 percent for Hispanic/Latino students.^[28]

Osteopathic medical school curricula are virtually identical to those at schools granting the MD degree (Doctor of Medicine). Once admitted to an osteopathic medical school, students study for four years in order to graduate. The schooling is divided into the pre-clinical and clinical years. The pre-clinical years, the first and second years, focus on the biomedical and clinical sciences. The clinical years, the third and fourth years, consist of core clinical training and sub-internships in the clinical specialties.

Osteopathic medical school accreditation standards require training in internal medicine, obstetrics/gynecology, pediatrics, family medicine, surgery, psychiatry, emergency medicine, radiology, preventive medicine, and public health.^[29] According to Harrison's Principles of Internal Medicine, "the training, practice, credentialing, licensure, and reimbursement of osteopathic physicians is virtually indistinguishable from those of physicians with MD qualifications, with 4 years of osteopathic medical school followed by specialty and subspecialty training and board certification".^[8]

DO schools provide an additional 300–500 hours in the study of hands-on manual medicine and the body's musculoskeletal system, which is referred to as osteopathic manipulative medicine (OMM).^[1] Historically, osteopaths subscribed to the view that such body manipulation can bring about systemic healing – a belief which is a form of pseudomedicine. In the early 21st century, American osteopathic physicians have largely shifted their thinking from such pre-scientific ideas.^[14]

Osteopathic physicians who use OMM predominantly use it to treat musculoskeletal conditions, for which there is conflicting evidence about effectiveness.^[30][31] Particular criticism has been targeted at craniosacral therapy, a component of OMM taught at many DO schools, which has limited scientific support.^[32][33]

Before entering osteopathic medical school, an applicant must complete a four-year undergraduate degree and take a national standardized exam called the Medical College Admissions Test (MCAT). Some combined undergraduate/medical programs exist. Some authors note the differences in the average MCAT scores and grade point average of students who matriculate at DO schools compared to those who matriculate at MD schools within the United States. In 2015, the average MCAT and GPA for students entering US-based MD programs were 31.4 and 3.70, respectively,^[34] and 27.33 and 3.55 for DO matriculants,^[35] although the gap has been getting smaller every year.^[35] DO medical schools are more likely to accept non-traditional students,^[36][37] who are older and entering medicine as a second career, or coming from non-science majors.

DO medical students are required to take the Comprehensive Osteopathic Medical Licensure Examination (COMLEX-USA), which is sponsored by the National Board of Osteopathic Medical Examiners (NBOME). The COMLEX-USA is series of four osteopathic medical licensing examinations. The first three exams of the COMLEX-USA are taken during medical school and are prerequisites for osteopathic residency programs, which are available in almost every specialty of medicine and surgery. Level 2 consists of a multiple-choice portion and a patient evaluation exam (2PE). COMLEX-Level 2PE, is available only in Chicago, IL and Philadelphia, PA. It is graded as a Pass/Fail exam. Finally, COMLEX Level 3 is taken during the first year of residency.

In addition to the COMLEX-USA, DO medical students may choose to sit for the MD licensure examinations, which are called the United States Medical Licensing Examination (USMLE).^[38] This is typically done if the student desires to enter an MD residency. However, this is not always required, as some MD residency programs do not require the USMLE from DO applicants.^{[39][40][41][42]} USMLE pass rates for DO and MD students in 2012 are as follows: Step 1: 91% and 94%, Step 2 CK: 96% and 97%, and Step 2 CS: 87% and 97%, respectively (this number may be misleading as only 46 DO students compared to 17,118 MD students were evaluated for Step 2 CS) Step 3: 100% and 95% (this number may be misleading, as only 16 DO students compared to 19,056 MD students, were evaluated for Step 3).^[43]

To obtain a license to practice medicine in the United States, osteopathic medical students must pass the Comprehensive Osteopathic Medical Licensing Examination (COMLEX),^[44] the licensure exam administered by the National Board of Osteopathic Medical Examiners throughout their medical training. Students are given the option of also taking the United States Medical Licensing Examination (USMLE) to apply for some Accreditation Council for Graduate Medical Education (ACGME) residency programs. Those that have received or are in the process of earning an MD or DO degree are both eligible to sit for the USMLE. Because of their additional training, only DO candidates are eligible to sit for the COMLEX.^[45]

Upon completion of internship and residency requirements for their chosen medical specialty, and depending on whether the program attended as ACGME or AOA accredited, holders of the DO may elect to be board certified by either a specialty board (through the American Medical Association's American Board of Medical Specialties) or an osteopathic specialty board (through the American Osteopathic Association Bureau of Osteopathic Specialists certifying boards). In February 2014, the American Osteopathic Association and the Accreditation Council for Graduate Medical Education agreed to unify allopathic and osteopathic Graduate medical education starting in 2020.^[46]

Depending on the state, medical licensure may be issued from a combined board (DO and MD) or a separate board of medical examiners.^[47] All of the 70 state medical boards are members of the Federation of State Medical Boards.^[48]

Currently, there are no osteopathic programs located outside of the United States that would qualify an individual to practice as an osteopathic physician in the United States.^[49] Foreign osteopathic degrees are not recognized by any state in the US as being equivalent to American DO degrees.

The following is an international licensure summary for US-trained doctors of osteopathic medicine, as listed by the American Osteopathic Association:^[50][51]