Do Birth Control Pills Work When...?


"Do birth control pills work when I...?"

This is a common question for women who are taking oral contraceptives, or “the pill.”

The pill has been the most popular non-permanent birth control in the US since 1982. The reason? If used correctly and consistently, the pill is more than 99% effective at preventing unwanted pregnancies.

However, the pill isn’t quite as effective if you don’t take it the correct way. There are also personal and lifestyle factors that can lower its effectiveness.

Here are five times when the pill might not reach that 99% effectiveness level.

You miss a pill—or take it too late

There are two types of birth control pills: combined pills that contain the hormones estrogen and progestin, and “mini-pills” that only have progestin.

If you’re on the combined pill, taking a pill late—by a few hours or even by a day— isn’t quite such a big deal. As long as you take your missed one right away, your risk of pregnancy is still low. Also, you don’t need to use a backup method of birth control, such as condoms.

However, if you miss two or more pills, your risk of pregnancy increases, you should use a backup method of birth control for at least seven days, and go straight to a new pack of pills instead of taking the “sugar pills” at the end of the pack The riskiest time to miss pills is at the beginning of a pill pack, so make sure you are ready with your new pack before your first pack finishes. Call your doctor if you miss two or more pills, as instructions on what to do may differ depending on where you are in your pill pack.

On the other hand, timing is everything if you’re on the mini-pill.

If you miss taking the mini-pill, take a pill as soon as possible. Take your next pill at the usual time, and go back to resuming your daily schedule of pills. Use a backup method of birth control for 48 hours after you’ve missed your dose.Mini-pill graphic

You are taking certain antibiotics

You might have heard people say that antibiotics decrease the effectiveness of the pill. It’s a common perception, but it’s only partly true. Most common antibiotics do not change the effectiveness of the pill.

The only antibiotic that has been shown to interfere with the pill is Rifampin , a drug most commonly used to treat tuberculosis. It is also sometimes prescribed to treat infections caused by other types of bacteria, or as a way to prevent infection in people who have come into close contact with someone who has certain serious bacterial infections.

Griseofulvin can also cause the pill to be less effective. This isn’t an antibiotic, but it’s a short-term medication used to treat fungal infections of the fingernails, toenails and scalp, and skin infections like athlete’s foot, ringworm, and jock itch.

You’re getting treatment for a chronic condition

If you are being treated for chronic conditions like HIV or sleep disorders , your treatment could reduce the effectiveness of the pill. This is especially important to keep in mind if you are on anti-seizure medications.

Anti-seizure medications aren’t just used for people with epilepsy—they’re also used to treat other conditions like migraines or bipolar disorder. And while some of the common ones, like lamotrigine (Lamictal) and levetiracetam (Keppra), have no effect on the pill, others can make the pill less effective.

Certain anti-seizure medications are called liver enzyme-inducing drugs because your liver is the organ that breaks down hormones in the drugs. These drugs can decrease sex hormone levels in women taking the pill, lowering the effectiveness of the pill and increasing your risk of getting pregnant.

If you take any of these medications , the pill might not be as effective:

  • Carbamazepine (Tegretol, Carbatrol)
  • Oxcarbazepine (Trileptal)
  • Phenytoin (Dilantin)
  • Phenobarbital (Luminal)
  • Primidone (Mysoline)
  • Topiramate (Topamax)

And a quick reminder: Some birth control pills can lower the effectiveness of anti-seizure medications . If you want to start the pill, be sure to talk to your physician about how the medicines might interact.

You’re going the natural route

Herbal supplements are natural, so they’re completely safe... right?

Not exactly. Some are, some are not . But even the ones that are safe can have undesirable effects, especially if you’re trying to avoid getting pregnant.

Women often use herbal supplements to improve fertility, meaning that they might have the opposite effect that you’re looking for. Be especially careful if you use St. John’s wort or Alfalfa . Both of these herbs have been shown to lower the effectiveness of the pill.

You’re trying to use them to prevent Sexually Transmitted Infections (STIs)

Birth control pills are just that: birth control. They can be extremely effective at helping you avoid an unwanted pregnancy, but they cannot prevent against STIs. Always use a barrier method like a condom to protect yourself from infections, such as HIV, HPV, chlamydia, and gonorrhea.

If you find that it’s tough to keep up with taking pills correctly, consider asking your doctor about a intrauterine device (IUD) or an implant – these methods work even better than pills to prevent pregnancy.

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