Oral Contraceptives/Penicillins Interactions

This information is generalized and not intended as specific medical advice. Consult your healthcare professional before taking or discontinuing any drug or commencing any course of treatment.

Medical warning:

Moderate. These medicines may cause some risk when taken together. Contact your healthcare professional (e.g. doctor or pharmacist) for more information.

How the interaction occurs:

When these two medicines are taken together, the penicillin medicine may alter the way your body processes the birth control pill.

What might happen:

The effect of your birth control pills may decrease and cause breakthrough bleeding, spotting, or even unintended pregnancy.

What you should do about this interaction:

General consensus is that a backup method of birth control is not needed while taking this antibiotic. If you have questions or concerns, discuss them with your healthcare professional (e.g. doctor or pharmacist).Your healthcare professionals may already be aware of this interaction and may be monitoring you for it. Do not start, stop, or change the dosage of any medicine before checking with them first.

View Reference
  • 1.Friedman CI, Huneke AL, Kim MH, Powell J. The effect of ampicillin on oral contraceptive effectiveness. Obstet Gynecol 1980 Jan;55(1):33-7.
  • 2.Back DJ, Breckenridge AM, Crawford FE, MacIver M, Orme ML, Rowe PH. Interindividual variation and drug interactions with hormonal steroid contraceptives. Drugs 1981 Jan;21(1):46-61.
  • 3.DeSano EA Jr, Hurley SC. Possible interactions of antihistamines and antibiotics with oral contraceptive effectiveness. Fertil Steril 1982 Jun; 37(6):853-4.
  • 4.Bainton R. Interaction between antibiotic therapy and contraceptive medication. Oral Surg Oral Med Oral Pathol 1986 May;61(5):453-5.
  • 5.Silber TJ. Apparent oral contraceptive failure associated with antibiotic administration. J Adolesc Health Care 1983 Dec;4(4):287-9.
  • 6.True RJ. Interactions between antibiotics and oral contraceptives. JAMA 1982 Mar 12;247(10):1408.
  • 7.Rubin DF. Antibiotics and oral contraceptives. Arch Dermatol 1981 Apr; 117(4):189.
  • 8.Trybuchowski H. Effect of ampicillin on the urinary output of steroidal hormones in pregnant and non-pregnant women. Clin Chim Acta 1973 Apr 19; 45(1):9-18.
  • 9.Willman K, Pulkkinen MO. Reduced maternal plasma and urinary estriol during ampicillin treatment. Am J Obstet Gynecol 1971 Mar 15;109(6):893-6.
  • 10.Sybulski S, Maughan GB. Effect of ampicillin administration on estradiol, estriol, and cortisol levels in meternal plasma and on estriol levels in urine. Am J Obstet Gynecol 1976 Feb 15;124(4):379-81.
  • 11.Boehm FH, DiPietro DL, Goss DA. The effect of ampicillin administration on urinary estriol and serum estradiol in the normal pregnant patient. Am J Obstet Gynecol 1974 May 1;119(1):98-103.
  • 12.Tikkanen MJ, Adlercreutz H, Pulkkinen MO. Effects of antibiotics on oestrogen metabolism. Br Med J 1973 May 12;2(5862):369.
  • 13.Back DJ, Breckenridge AM, MacIver M, Orme M, Rowe PH, Staiger C, Thomas E, Tjia J. The effects of ampicillin oral contraceptive steroids in women. Br J Clin Pharmacol 1982 Jul;14(1):43-8.
  • 14.Joshi JV, Joshi UM, Sankholi GM, Krishna U, Mandlekar A, Chowdhury V, Hazari K, Gupta K, Sheth UK, Saxena BN. A study of interaction of low-dose combination oral contraceptive with Ampicillin and Metronidazole. Contraception 1980 Dec;22(6):643-52.
  • 15.Adlercreutz H, Pulkkinen MO, Hamalainen EK, Korpela JT. Studies on the role of intestinal bacteria in metabolism of synthetic and natural steroid hormones. J Steroid Biochem 1984 Jan;20(1):217-29.
  • 16.Faculty of Sexual and Reproductive Healthcare Clinical Effectiveness Unit. Clinical guidance drug interactions with hormonal contraception. January, 2011.
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CONDITIONS OF USE: The information in this database is intended to supplement, not substitute for, the expertise and judgment of healthcare professionals. The information is not intended to cover all possible uses, directions, precautions, drug interactions or adverse effects, nor should it be construed to indicate that use of a particular drug is safe, appropriate or effective for you or anyone else. A healthcare professional should be consulted before taking any drug, changing any diet or commencing or discontinuing any course of treatment.