Selected Anticonvulsants; Barbiturates/Contraceptives 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.
Serious. These medicines may interact and cause very harmful effects. Contact your healthcare professional (e.g. doctor or pharmacist) for more information.
How the interaction occurs:
When these two medicines are taken together, your body may process the estrogen in birth control pills more quickly.
What might happen:
The effects of your birth control pills may decrease and cause breakthrough bleeding, spotting, or pregnancy. If you are taking a product containing phentermine and topiramate for weight loss, you may experience breakthrough bleeding, but it is not expected to decrease the effectiveness of your birth control.
What you should do about this interaction:
If you are taking medicine for seizures, talk to your healthcare professional (e.g. doctor or pharmacist) as soon as possible about using a different form of birth control. Contact your doctor if you experience breakthrough bleeding, spotting, or pregnancy, or if you have any seizures.If you are taking a product containing phentermine and topiramate for weight loss, let your doctor know if your bleeding patterns change. It is important to keep taking your birth control AND use a barrier method of contraception while using your phentermine and topiramate.Emergency contraceptives may be less effective also. You may need a larger dose than normal. Discuss the dose and the need to confirm that you do not become pregnant with a pregnancy test with your healthcare professional.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.
- 1.Copeman H. Oral contraceptives. Med J Aust 1963 Dec 7;2:969.
- 2.McArthur J. Oral contraceptives and epilepsy. Br Med J 1967 Jul 15;3:162.
- 3.Kutt H, McDowell F. Management of epilepsy with diphenylhydantoin sodium. Dosage regulation for problem patients. JAMA 1968 Mar 11;203(11):969-72.
- 4.Espir M, Walker ME, Lawson JP. Epilepsy and oral contraception. Br Med J 1969 Feb 1;1(639):294-5.
- 5.Kenyon IE. Unplanned pregnancy in an epileptic. Br Med J 1972 Mar 11; 1(801):686-7.
- 6.Janz D, Schmidt D. Letter: Anti-epileptic drugs and failure of oral contraceptives. Lancet 1974 Jun 1;1(7866):1113.
- 7.Laengner H, Detering K. Letter: Anti-epileptic drugs and failure of oral contraceptives. Lancet 1974 Sep 7;2(7880):600.
- 8.Roberton YR, Johnson ES. Interactions between oral contraceptives and other drugs: a review. Curr Med Res Opin 1976;3(9):647-61.
- 9.Coulam CB, Annegers JF. Do anticonvulsants reduce the efficacy of oral contraceptives?. Epilepsia 1979 Oct;20(5):519-25.
- 10.De Leacy EA, McLeay CD, Eadie MJ, Tyrer JH. Effects of subjects' sex, and intake of tobacco, alcohol and oral contraceptives on plasma phenytoin levels. Br J Clin Pharmacol 1979 Jul;8(1):33-6.
- 11.Back DJ, Bates M, Bowden A, Breckenridge AM, Hall MJ, Jones H, MacIver M, Orme M, Perucca E, Richens A, Rowe PH, Smith E. The interaction of phenobarbital and other anticonvulsants with oral contraceptive steroid therapy. Contraception 1980 Nov;22(5):495-503.
- 12.Notelovitz M, Tjapkes J, Ware M. Interaction between estrogen and dilantin in a menopausal woman. N Engl J Med 1981 Mar 26;304(13):788-9.
- 13.Dada OA, Martins OO. Drug effects on the intestinal absorption of estrogens. J Steroid Biochem 1983 Jul;19(1C):821-5.
- 14.Odlind V, Olsson SE. Enhanced metabolism of levonorgestrel during phenytoin treatment in a woman with Norplant implants. Contraception 1986 Mar;33(3):257-61.
- 15.Haukkamaa M. Contraception by Norplant subdermal capsules is not reliable in epileptic patients on anticonvulsant treatment. Contraception 1986 Jun;33(6):559-65.
- 16.Mattson RH, Cramer JA, Darney PD, Naftolin F. Use of oral contraceptives by women with epilepsy. JAMA 1986 Jul 11;256(2):238-40.
- 17.Crawford P, Chadwick DJ, Martin C, Tjia J, Back DJ, Orme M. The interaction of phenytoin and carbamazepine with combined oral contraceptive steroids. Br J Clin Pharmacol 1990 Dec;30(6):892-6.
- 18.Nor-Q-D (norethindrone) US prescribing information. WatsonPharma March, 2005.
- 19.Doose DR, Wang SS, Padmanabhan M, Schwabe S, Jacobs D, Bialer M. Effect of topiramate or carbamazepine on the pharmacokinetics of an oral contraceptive containing norethindrone and ethinyl estradiol in healthy obese and nonobese female subjects. Epilepsia 2003 Apr;44(4):540-9.
- 20.Topamax (topiramate) US prescribing information. Janssen Pharmaceuticals, Inc. May, 2019.
- 21.Therapeutic Goods Administration. Medicines Safety Update - Unintended pregnancy due to interaction between etonogestrel implant (Implanon) and carbamazepine. Australian Prescriber December, 2010;33(6):182-5.
- 22.Fycompa (perampanel) UK summary of product characteristics. Eisai Ltd May, 2017.
- 23.Qsymia (phentermine and topiramate extended-release) US prescribing information. Vivus, Inc. March, 2018.
- 24.Centers for Disease Control and Prevention. U.S. Medical Eligibility Criteria for Contraceptive Use, 2016. MMWR Recomm Rep. Available at: https://www.cdc.gov/mmwr/volumes/65/rr/pdfs/rr6503.pdf July 29, 2016; 65(3):.
- 25.Department of Reproductive Health World Health Organization. Medical eligibility criteria for contraceptive use. Fourth Edition 2010.
- 26.Medicines and Healthcare products Regulatory Agency. Levonorgestrel-containing emergency hormonal contraception: advice on interactions with hepatic enzyme inducers and contraceptive efficacy. available at: https://www.gov.uk/drug-safety-update/levonorgestrel-containing-emergency -hormonal-contraception-advice-on-interactions-with-hepatic-enzyme-induce rs-and-contraceptive-efficacy September 15, 2016..
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.