Lots more below:

The drugs that do and do not decrease the effectiveness of hormonal contraceptives are listed below:

Drugs that decrease pill effectiveness by increasing liver hormone breakdown:

Carbamazepine (Tegretol), Nevirapine, Oxcarbazepine (Trileptal), Phenobarbital, Phenytoin (Dilantin),

                Primidone (Mysoline), Rimidone (Mysoline), Rifabutin, Rifampicin, St. John’s Wort,

Topiramate (Topamax), Lamotrigine (Lamictal)*

*Lamictal is, itself affected by pills and pills affect Lamictal (more to follow- P52-Policar)

Drugs that do not cause induction of liver enzymes:

                Sodium Valproate (Depakote, Depakene), Clonazepire, Ampicillin, Clarithromycin, Metronidazole,

                Ciproflaxacin, Ofloxacin, Doxycycline, Fluconazole, Ethosuximide (Zarontin),

Levetiracetam (Keppra), Vigabatrin (Sabril), Zonigamite (Zonegram), Pregabalin (Lyrica),

                Clonazepam (Klonopin), Tigabine (Gabitril)

Possibly ethosuximide, griseofulvin, troglitazone, Vigabatrin and Provigil (modafinal) [Speroff, Darney; A Clinical Guide for Contraception.  Fourth edition 2005, page 101] [Guillebaud, Contraception: Your Questions Answered; Fourth edition, Pages 123-130] [Physicians Desk Reference 2007: p.990]

Broad-spectrum antibiotics:

“Broad-spectrum antibiotics such as amoxicillin and tetracycline, which alter the intestinal flora thought to be instrumental in promoting absorption of the sex steroids, do not reduce the efficacy of OC’s.  Women using the antibiotics do have statistically significant but not clinically lower serum levels of estrogen and progestins.  However, virtually every woman taking these antibiotics has remained well within the therapeutic range for the sex steroids.  ^168-170[Murphy 1991] [Neely 1991] [Friedman 1980].  As a result, back-up methods should not be necessary unless the patient has problems taking her pills, e.g., if her underlying medical condition interferes with pill taking or absorption.  Long-term use of broad-spectrum antibiotics (such as erythromycin or tetracycline for acne) is compatible with OC use; back-up methods are not routinely needed for pregnancy prevention. ¹⁷¹[Helms 1997]. 

Given all the conflicting messages, here is an attempt at summarizing, but not cutting through, the confusion regarding the antibiotics most women and their health care providers are most concerned about:

If you are taking a broad spectrum antibiotic such as tetracycline, doxycycline, ampicillin or erythromycin, some clinicians recommend that you use a back-up contraceptive, others do not. Some women taking these broad spectrum antibiotics use a back-up contraceptive, others do not. The decision is up to you.

Here are the words of advice from the Planned Parenthood Federation of America: "There is no pharmacologic evidence that the acute or chronic use of systemic antibiotics (e.g. tetracycline, ampicillin) decreases the efficiency of low-dose COCs in women who take them correctly."

To learn more about the advantages and disadvantages of all birth control pills, go to our website: www.managingcontraception.com and click on Choices.  You can also order this wonderful new educational book from our website or by calling 404-875-5001.  Do you have your copy yet?