What medications counteract the Pill?

Which drugs might impact the efficacy of the birth control pill? Comments are offered by Andrew Kaunitz, MD, professor and assistant chair in the obstetrics and gynecology department at the University of Florida Health Science Center/Jacksonville, and Susan Wysocki, RNC, NP, president and chief executive officer of the National Association of Nurse Practitioners in Women’s Health.

Question: Would you please tell me what medications counteract with the birth control pill? A patient told me that she got pregnant after Nyquil cold medicine interacted with the pill. Is that possible?

Kaunitz: When looking at concomitant use of medications in women using oral contraceptives (OCs), know that anticonvulsants represent the class of medications taken by U.S. reproductive age women that are most likely to impair OC efficacy. Since seizures increase during pregnancy and many anticonvulsants are teratogens, ensuring highly reliable contraception represents a health care priority in women taking anticonvulsants.1

Clinicians should be aware that an increasing number of women who do not have seizure disorders are taking anticonvulsants for such conditions as bipolar disorder, migraine headaches, and chronic pain syndromes.

Some anticonvulsants induce hepatic enzymes, resulting in lower estrogen and progestin levels in women using OCs. Anticonvulsants known to induce hepatic enzymes include barbiturates, primidone, carbamazepine, felbamate, oxcarbazepine, phenytoin, and topiramate.2 Anticonvulsants that do not induce hepatic enzymes include benzodiazepines, ethosuximide, gabapentin, lamotrigine, levetiracetam, tiagabine, valproic acid, vigabatrin, and zonisamide.2

Although it makes sense to be concerned that enzyme-inducing anticonvulsants indeed reduce OC efficacy, the good-quality data available focus on steroid blood levels, not pregnancy rates. Some experts recommend use of 50 mcg estrogen pills for women using anticonvulsants.3 Certainly, it makes sense to avoid use of OCs formulated with fewer than 30-35 mcg estrogen in women taking anticonvulsants known to induce liver enzymes.

Progestin-only (mini) pills are associated with lower serum progestin levels than in women using combination OCs; therefore, minipills are not appropriate contraceptive choices for women using anticonvulsants that induce liver enzymes.4

Regarding interactions of medications other than antiepileptics with OCs, the primary problem is the antibiotic rifampin, a potent enzyme-inducer. Antibiotics including tetracycline, quinolones, metronidazole, and ampicillin, when used as monotherapy, have not been found to decrease steroid levels in women taking OCs.5 It may be prudent, however, to recommend condom backup for women taking two antibiotics simultaneously.

Wysocki: Refer to the Geneva-based World Health Organization (WHO) site with the latest medical eligibility criteria for contraceptive use. (Go to the WHO web site, www.who.int. Click on "WHO sites," "Reproductive Health and Research," and "Third edition of the Medical Eligibility Criteria for Contraceptive Use.")

Nyquil (or its chemical equivalent) is not listed in the drug interactions section.


1. Holmes LB, Harvey EA, Coull BA, et al. The teratogenicity of anticonvulsant drugs. N Engl J Med 2001; 344:1,132-1,138.

2. Crawford P. Interactions between antiepileptic drugs and hormonal contraception. CNS Drugs 2002;16:263-272.

3. Mattson RH, Rebar RW. Contraceptive methods for women with neurologic disorders. Am J Obstet Gynecol 1993; 168(6 Pt 2):2,027-2,032.

4. Kaunitz, AM. Revisiting progestin-only OCs. Contemporary OB/GYN 1997; 91-104.

5. American College of Obstetricians and Gynecologists. The Use of Hormonal Contraception in Women with Coexisting Medical Conditions. ACOG Practice Bulletin 2000; 18:7.