Birth Control


Your odds of getting pregnant while on birth control depends on the type of birth control that you are using, as well as how you are using that birth control.  Assuming that you are taking your birth control exactly as it has been prescribed to you, you will only have a one in 1000 chance of getting pregnant, or a 0.1 percent chance. If, however, you forget to take one or more pills during a month, of if you take a pill too late in the day, then your chances of getting pregnant rise to 5 percent, or 1 in 20, according to Palo Alto Medical Foundation.

In fact, of the 62 percent of women in America who use contraception today, the birth control pill is the most popular form. More than 10.5 million women in America use the pill, state the Centers for Disease Control and Prevention. Less than one in every 100 women who take the pill each day will become pregnant; however, 9 in 100 women who sometimes forget to take their pill each day, or take it at the wrong time, will become pregnant.

Remember, the birth control pill is only 99.9 percent effective in preventing pregnancy and that is only IF you take it exactly as your doctor recommends.

Besides not taking the pill regularly and on time, there are a few more reasons why you can get pregnant while on birth control.


Alcohol can weaken the effectiveness of birth control pills. This is because your liver metabolizes alcohol, and any substance that affects the liver can affect how your body absorbs the pill.

Antibiotics and Medications

There are some types of medications that produce liver enzymes, and this can create lower hormone levels. Because of this, and the fact that most birth control pills already contain low dosages of estrogen, these drugs may be more likely to decrease the overall effectiveness of the birth control pill. This is a partial list of such medication as listed by the University of North Carolina Campus Health Services:

  • Antibiotics, such as Rifampin, Rifadin, Rimactane, Ampicillin, and Tetracylines
  • Antifungals, such as griseofulvin (Gris-Peg)
  • Seizure medications and mood stabilizers, such as Oxcarbazepine (Trileptal), carbamazepine (Tegretol), felbamate (Felbatol), topiramate (Topamax), phenytoin (Dilantin), lamotrigine (Lamictal), and primidone (Mysoline)
  • Barbiturates, such as secobarbital (Seconal), phenobarbital (in Donnatal), and butalbital (Fiorinal, Esgic Plus)
  • Certain Antivirals used for HIV infection, such as nelfinavir (Viracept) and lopinavir (Kaletra)
  • Herbal supplements, such as St. John’s Wort

If you know that you have to take one of the above medications for a short time, then you must also use a backup birth control method for the duration of the medication plus four weeks after completing the medication. If you know that you will need to take the medication on a long-term basis, you should definitely talk with your doctor to discuss an alternative form of contraception.

Using Backup Birth Control Methods

To eliminate any chances of falling pregnant while on birth control, you should consider using multiple birth control methods at the same time. Although the most common form of birth control is the pill, it does not prevent against STDs. Therefore, it is a good idea to use another barrier method of birth control that does protect against STDs.

Other times to use a backup method of birth control:

  • During the first seven days of starting the pill, especially if you use the Sunday or Quick start birth control pills.
  • If you vomit within the first two hours after taking an active pill, then you must treat it as a missed pill.
  • You should also treat it as a missed pill if you experience severe diarrhea (> 3 loose stools in 24 hours).

Other Methods of Birth Control

The least reliable method of birth control is the ‘natural method’. These include the Withdrawal Method and the Rhythm Method. With the Withdrawal Method, the chance is around four percent in getting pregnant. With the Rhythm Method, you will only have a 1-9 percent chance of falling pregnant, depending on the individuals and how exactly the method is observed.

A barrier method of birth control is usually a better bet. These include using a sponge to provide you with a 9 percent conception chance.  These chances diminish to six percent when using only spermicide or a diaphragm.  Using a female condom gives you a five percent chance, while using a male condom gives you a three percent chance of falling pregnant. If you combine one of the other methods with just spermicide, you can increase effectiveness to around 99%.

The best statistics, however, are those provided by hormonal methods of birth control. Norplant is 99.91% effective, for example.  The Depo-Provera shot offers a 99.7% effective rate, while birth control pills are around 99.9% effective.

Contrary to popular belief, surgical methods of sterilization, like vasectomies or having your tubes tied, are not 100% effective. In fact, having your tubes tide leaves you with only a 99.96% success rate, while a vasectomy is almost 99.5% effective.