Q: If I have a title with a colon, is the first word after the colon capitalized or lowercased?
A: If you are speaking about title and subtitle on the manuscript itself, every major word in the title and subtitle, as well as the first word of title and subtitle, would begin with a capital letter.
Endless and Essential: The Tug-of-War Over Off-Label Use
If you are speaking about the title and subtitle of a journal article as it appears in the reference list, only the first word of the title and any proper nouns would begin with a capital letter.
19. Incollingo J. Endless and essential: the tug-of-war over off-label use. Cataract & Refractive Surgery Today. 2016;16(5):19-27.
More about capitalization of titles can be found in chapter 10.—Cheryl Iverson, MA