- Inconsistency. Taking your pill at the exact same time every day greatly reduces the risk of failure. And while obesity used to be considered a factor that could impact the effectiveness of the pill, a recent study said consistency, not weight has the greatest impact. If you forget to take more than one pill in a month, be sure to use backup birth control and call your doctor or pharmacist for specific advice.
- St. John's Wort. The natural supplement can increase the breakdown of your pill's estrogen, making it less effective.
- The antibiotic rifampin. According to the Mayo Clinic, the risks of antibiotics interfering with the pill are greatly overstated. Yet, the antibiotic rifampin (Rimactane) does have an impact, so check with your doctor if you are prescribed antibiotics.
- Other medications. Some yeast-infection medicines, HIV treatments, or anti-seizure medication could counteract the pill. If you ever fill a new prescription, always ask if you need to use a backup form of birth control.
- Temperature. Be sure to store your pack in a cool place. If it's left in the sun or in extreme heat (or cold) it could become less effective.
- Vomiting or diarrhea. If you're ill within 30 minutes of taking your pill — thanks to alcohol or something else — treat it as if you missed it.
If you want to (or can't help but) forget the pill, there's always nonhormonal birth control.