I had one mild case of diarrhea after taking my last active pill of my birth control pack. I'm on the combined pill Gildess fe 1.5/30 and have not missed any pills. I have been on it for over a year. Will one episode of diarrhea about 14 hours after taking the pill reduce the effectiveness? I think my upset stomach was due to what I had for dinner a few hours before taking my pill the night before.