Understanding the relationship between antibiotics and birth control is crucial if you wish to prevent an unplanned pregnancy. Stories abound online and in real life about pregnancies resulting from the use of antibiotics or other medications while using the birth control pill. However, there isn't enough scientific research to provide hard evidence for or against this interaction. Many physicians recommend a second method of birth control just in case.

Do Antibiotics Impact Birth Control Pills?

Women have been hearing stories for years about how taking penicillin or other antibiotics can interfere with the effectiveness of birth control pills. However, according to the Mayo Clinic, no large, long-range studies have proven antibiotics to cause major interference with the pill. Only one antibiotic, rifampin, has been shown to definitively cause loss of effectiveness.

Of course, a small percentage of women may experience decreased effectiveness with the use of other antibiotics, so doctors usually advise all women to use a condom or other backup method of birth control while on antibiotics. There is no way of knowing if you are in that percentage until it is too late. New versions of the birth control pill in low-dose form may be more prone to this problem.

Many physicians believe that antibiotics interfere with the metabolization of birth control pills. Birth control pills usually carry a 95 to 99 percent effectiveness rate. The studies that have been done show a very small difference in effectiveness when the woman is also taking antibiotics. Usually the difference is less than one percent. A partner taking antibiotics will not interfere with a woman's use of birth control pills.

Drugs to Avoid

Although there are varying degrees to which antibiotics may affect hormonal birth control, there are certain drugs which doctors say can cause decreased effectiveness. You may be asking yourself, does Sulfamethoxazole Trimethoprim affect birth control? Can you take Nitrofurantoin and birth control? Medications (antibiotic and otherwise) that are commonly listed as interfering with birth control include the following:

Rifampin -- often prescribed for tuberculosis

Penicillin

Amoxicillin

Sulfonamide

Sulfamethoxazole and trimethoprim

Ampicillin

Cotrimoxazole

Tetracycline

Griseofulvin -- antifungal medication

Minocycline

Phenobarbitol -- anti-seizure medication

Metronidazole

Nitrofurantoin

Certain anti-HIV protease inhibitors

St. John's Wort

If your medication or antibiotic is not on this list, that does not mean it will not have a nominal effect. Check with your healthcare provider if you have any questions regarding your birth control effectiveness while on medication.

Use a Second Form of Contraception

If you are taking any of the listed antibiotics along with birth control pills, physicians recommend that you use a second method of birth control to be on the safe side. The second method should be used while taking the antibiotics and continued for a week afterwards. Other hormonal methods, like the patch or the ring, can also be affected by antibiotics, so you shouldn't use one of those as your backup.

Stopping your pills while on antibiotics will only cause your body to unnecessarily reprogram itself. Instead, find a barrier method to use until your prescription runs out. Discuss your individual concerns about antibiotics and birth control effectiveness with your doctor.

Antidepressants and Birth Control

If you have been prescribed antidepressants, such as Prozac, and are on birth control, it is generally considered safe to take them at the same time. The antidepressants will not cause your birth control to lose its effectiveness. But it's still recommended that you discuss all medications you've been prescribed or are taking with your doctor in order to avoid any potential drug interactions.

You should keep in mind that the various antidepressants each have their own list of potential side effects as do the various hormonal birth control. There is a possibility that if combined, there could be side effects from the medications which can actually vary from person to person. However, there should still be no change to the efficacy of either medication. If you do experience any side effects from the medications, your doctor will reevaluate and determine what works best for your specific needs.

Alert Your Physician to Any Medication Use

Most women and physicians prefer to err on the side of caution when it comes to antibiotics and birth control. Despite the fact there is little evidence supporting a massive increase in pregnancies with antibiotic use, it is better to be safe than sorry.

Always tell your physician if you are taking any medications while on the birth control pill. A pharmacist can also answer drug interaction questions. Or, you can call Planned Parenthood at 1-800-230-PLAN to find a center near you, if you do not have a healthcare provider and have questions regarding pregnancy, the pill, and antibiotics.