Since 1999 America has accounted for 71% of the sales of new chemical entities, up from 62%. Japan and Germany, the next two largest pharmaceutical markets, account for just 4% each.
That is from Doug Bandow at Cato, here is the link. Of course this figure stems from both high volume and high price in the U.S.; it is a massive form of implicit foreign aid. By the way, for those of you interested in Cato University seminars on economics — "for citizens" — read more here.