How much less effective are birth control pills if you have diarrhea?

Still effective: Generally speaking, diarrhea will not decrease absorption (or efficacy) of birth control pills. Hopefully, the diarrhea is a temporary or episodic condition, and please see your doctor if diarrhea becomes a prolonged or chronic problem. Did the diarrhea start after bcp (then it may be a side effect, and STILL would NOT decrease efficacy).

No impact: Diarrhea should not impact the efficacy of you birth control.