Its the under that interests me.
"The global market for over-the-counter (OTC) drugs is expected to surpass $70 billion by 2015, reports Visiongain. According to estimates from the Consumer Healthcare Products Association, retail sales of OTC medicines in the US in 2010 were worth $17 billion, unchanged from the preceding year, and showing an increase over more than $3 billion over a ten-year period."
That was taken from http://www.reportlinker.com/ci02262/Over-The-Counter-Drug.html
in a word.... A LOT
Well, that statistic says US specifically... I'm glad I left the link so you can go there and be able to cite it on your paper. Good job not waiting till the last minute. My boolean search string was "statistics sales US over-the-counter drugs"