Pills and Antibiotics

If possible, you should avoid taking other medicines, or herbal remedies, with the contraceptive pill. If a health professional prescribes medicine for you, you should always tell them if you're taking the pill. This is because some medication can affect the way that the pill works. Antibiotics might decrease the effectiveness of birth control pills (contraceptives). There have been reports of pregnancy in women who have taken antibiotics while using birth control pills.

Theoretically, additional medications might alter the metabolism and blood levels of the birth control hormones, thereby altering their effectiveness. Antibiotics can affect how estrogen (the active ingredient in the contraceptive pill) is absorbed into your body. This can make the pill less effective, and you'll need to use an additional form of contraceptive, such as a condom. You should use the additional form of contraceptive while you're taking antibiotics, and for one week after you stop.

Some antibiotics can interact with birth control pills, making the birth control pills less effective and pregnancy more likely. Spotting or so called “mid-cycle bleeding” could be the first sign that an antibiotic is interfering with the effectiveness of your birth control pills.

Antibiotics that have been shown to interact with birth control pills include rifampin (brand name Rifadin), and to a lesser extent, penicillin (Veetids), amoxicillin (Amoxil), ampicillin (Omnipen), sulfamethoxazole/trimethoprim (Septra or Bactrim), tetracycline (Sumycin), minocycline (Minocin), metronidazole (Flagyl), and nitrofurantoin (Macrobid or Macrodantin).

Nevertheless, it is noteworthy that antibiotics, such as rifampin, ampicillin, tetracylines, and griseofulvin have been reported to cause breakthrough bleeding and menstrual irregularities in women taking birth control pills. Similar effects have also been reported in women taking the seizure medications phenytoin and barbiturates.

To help women avoid pregnancy while taking an antibiotic - and for at least one week afterward - doctors generally recommend they use a condom or spermicide as a back-up method of birth control. If you are taking both antibiotics and birth control pills, be sure to check with your doctor about how long you should continue to use a back-up method. Also, discuss any other questions you may have about this information.

TIPS for women who should take antibiotics while using birth control pills

For avoiding pregnancy while taking pills and antibiotics – use condom or spermicide as a back-up method of birth control (at least during and one week afterward!)

There are two main types of pill. The first is the monophasic, or phasic pill, which you take for 21 days, and then take no pills for the next seven days.

The second is the 'Everyday' pill, where there are 21 active pills and seven inactive pills which don't contain any hormones (placebos). These look different to the active pills. You take one pill a day for 28 days - three weeks on the active pill, and one week on the inactive pill, with no break between packets.

If you're taking monophasic, or phasic pills, and you get to the end of your packet, while you're taking antibiotics, don't have the usual seven day break. Start your new pill packet straight away.

Similarly, if you're taking the Everyday pill, while taking antibiotics, and you get to the end of your active pills, don't take the seven day course of inactive pills. Start a new course of active pills.

If you're taking antibiotics during the first seven days of your new pill packet, and you've had sex within the last 5-7 days, you should seek medical advice because you may also need emergency contraception. This is because the antibiotics may have disrupted the normal protection provided by your pills, and there is a chance that you might have become pregnant.

If you're required to take antibiotics for more than two weeks, you may need to follow different instructions. Your GP should be able to provide advice.