Antibiotics and Birth Control

From LoveToKnow Pregnancy

Understanding the link 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. But, because no method of birth control is guaranteed 100 percent, can we trust the stories we hear? Sorting it out can be confusing.

Antibiotics and Birth Control

Antibiotics and Birth Control: Fact or Fiction?

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, a leading healthcare facility, no large, long-range studies have proven antibiotics to cause major interference with the pill. Only one antibiotic, rifampin, has 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 decreased effectiveness.

Antibiotics are thought to interfere with the metabolization of birth control pills. Birth control pills are usually given a 95 to 99 percent effectiveness rate. The studies that have been done show a very small difference in effectiveness. Usually the difference is less than 1 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. Medications (antibiotic and otherwise) that are commonly listed as interfering include:

  • Rifampin
  • Penicillin
  • Amoxicillin
  • Sulfonamide
  • Ampicillin
  • Cotrimoxazole
  • Tetracycline
  • Griseofulvin
  • Minocycline
  • Phenobarbitol
  • Metronidazole
  • Nitrofurantoin

Taking a medication or antibiotic that is not on this list 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.

If you are taking any of the listed antibiotics and 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 continue for a week afterwards.

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.

Concluding Arguments

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.


 


Comments

Lauren, ask your pharmacist or doctor for another opinion, but personally, I think you should use a backup until you get your next period. I'm very conservative on this though and others will tell you differently.

If you don't get your period, take a pregnancy test. If it's negative but your period is late, wait a few more days and test again.

-- Contributed by: HollySwanson

I have been on tri-legest for the past 4 years and this week was put on the z-pack for an ear infection. I forgot to use a back up method, and my boyfriend came in me. I start my sugar pill week in four days. Should I take a pregnancy test, and when? And should a back up method be used all of next month as well since my last z-pack pill is on the first day of my period?

-- Contributed by: Lauren

Just a note on something that needs to be cleared up: while on the pill, you have NO "normal ovulation time" - whether around day 14 or not. The 28-day cycle only applies to women who (1) are not on the pill and (2) have a very regular cycle. One of the primary modes of pregnancy prevention while on birth control is that you don't ovulate at all, and in the event this mechanism fails, you're just as likely to have breakthrough ovulation on day 3 as you are day 13 and day 28. Ovulation while you're on the pill would be the result of taking it incorrectly, taking a medicine that interfered, or being part of that 1-ish% the pill just fails for...and it can happen at any point during the cycle. It is NOT being controlled by your natural cycle rhythm. There is NO reason that "if" you were going to ovulate while you're on the pill, it would be more likely to come mid-cycle. You have no set "fertile time" while on the pill or any time that you're more likely to get pregnant than any other, barring other factors like medication, forgetting to take pills, etc. Even if you're on antibiotics during the first of your pack and you ovulate, it's most likely going to happen within a few days of beginning those antibiotics - your body won't wait until day 14 and say, "Oh! I'm supposed to pop out this egg now!" It just doesn't work that way. Being around day 14 while on the pill has no special effect or meaning for anything.

Also it's also commonly recommended that after taking an antibiotic, protection is generally only needed for two weeks of ACTIVE PILLS maximum. That means that no matter where you are in your pack, whether at the beginning or the end, you need 7 to 14 ACTIVE pills between when you stopped your medication and when you have unprotected sex if you're trying to avoid pregnancy. Your sugar (period week) pills don't count toward this - you need to take enough active pills from your next pack to meet the 7-14 active pill threshold to be on the safe side.

-- Contributed by: Lena
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