Source: http://chroniclingamerica.loc.gov/lccn/sn82014086/1918-01-11/ed-1/seq-4/

The prohibition amendment is moving through the state ratification process, yet "nightcaps" as a solution for colds and flu are still being recommended by "medical men." The abnormal times when so many people (troops) are outside during the night is assumed to be the basis of the popularity.

Source: "Night-caps," Norwich Bulletin, Norwich, Connecticut, January 11, 1918. Page 4, Column 4.