Here’s a FAQ from the FDA about quinine. The first question and answer states:
What action is FDA taking concerning quinine-containing drugs?
FDA has ordered all firms to cease manufacturing unapproved products containing quinine, including quinine sulfate and any other salt of quinine on or after February 13, 2007, and to cease shipping such products interstate on or after June 13, 2007. After these dates only FDA approved quinine products may be manufactured and shipped interstate. This action is described in the Federal Register of December 15, 2006, [71 FR 75557].
http://www.fda.gov/cder/drug/unapproved_drugs/quinineQA.pdf
Here’s a letter to a doctor from the FDA about quinine water which seems to imply that it is not under the restriction because the amount of quinine is minimal. However, I know people that have drunk quinine water (tonic water) in the evening to avoid nocturnal cramps.
http://aap.org/sections/seniormembers/docs/Quinine.pdf