A Doctor of Medicine, abbreviated MD, was a degree and a title awarded to a student at a medical college. An individual who earned an MD could be a physician, a surgeon, or both. Originally from pre-Federation Earth, this degree was assimilated into the Federation educational system in the 22nd century.
In 2365, according to a directory on Starbase 515, several doctors had earned this title and were posted to this base. They were Brian Faul, Sam Freedle, Les Landau, Scott Luhrsen, Robert McCullough, Robert Metoyer, and Adele Simmons.
Medical careers in Starfleet varied depending upon specialties. In order to be a chief medical officer, a physician was required to be highly skilled in both surgery as well as in general medicine. (citation needed • edit)
It was an academic degree, as well, in the 29th century. Some of the bearers of this degree worked at the Temporal Integrity Commission. On the dedication plaque of the USS Relativity, Professor R. Picardo was listed with this degree. (VOY: "Relativity", dedication plaque)