My girlfriend took antibiotics while taking lo loestrin fe. is it true that antibiotics affect the effectiveness of the pill? and for how long?

Reading Instructions: Yes it is very much a fact that antibiotics and certain other medications can make birth control ineffective or less effective. These are clearly pointed out in the written information every female in the U.S. Gets when they pick up their prescription. The length of interruption can vary depending on the medication. Women on birth control must use other barrier forms to prevent pregnancy then.

Yes: Not all antibiotics will do this but many will interfere with the effectiveness of birth control pills. In general when on both oral contraceptives and antibiotics it is best to use another method for that cycle.