RT Journal Article SR Electronic T1 Oral contraceptives and risk of gallbladder disease JF Canadian Medical Association Journal JO CMAJ FD Canadian Medical Association SP 1517 OP 1517 DO 10.1503/cmaj.111-2066 VO 183 IS 13 A1 Mayhar Etminan YR 2011 UL http://www.cmaj.ca/content/183/13/1517.3.abstract