Around 45 million Americans — 18 percent of the adult population — said last year they did not fill a prescription due to cost, according to an analysis of data from the Commonwealth Fund by Gabriel Levitt, president of PharmacyChecker.com, whose company helps Americans buy medications online by vetting overseas pharmacies and comparing prices for different drugs. Data compiled by the company comparing prices offered in Canada to those in New York, shows drugs are frequently three times or more as costly in the U.S. as over the border.