Can cefdinir interact birth control? can it cause vaginal spotting? thank you

Little or no risk: The idea that antibiotics make birth control pills (or other hormonal contraception) ineffective isn't quite an urban myth, but almost. This is extremely rare if it occurs at all. No antibiotic causes vaginal bleeding, and any new or unexplained vaginal bleeding -- even minor "spotting" -- needs professional evaluation. Contact your doctor. Good luck.