Birth control discharge

so i recently started a birth control as part of a clinical trial study. since i started it, ive had this weird brownish discharge every so often. other than being a lil embarrassing there really isnt much else i was just worried because its not my cycle. i took a test and im not pregnant so i ruled out implantation bleeding.  again this is my first month on birth control so i havent even gotten my first cycle on it. does anyone have any experience or reassurance for me? thanks!