Plan B Side Effects

Nausea, fatigue, and headaches are among the most commonly reported Plan B side effects. These tend to be minor and are generally easily to treat. However, there are some potentially serious side effects of Plan B that should be reported to a healthcare provider right away, including vomiting within one hour of taking a tablet, signs of an ectopic pregnancy, and allergic reactions.

An Introduction to Plan B Side Effects

Just like any medicine, Plan B One-Step™ (levonorgestrel) can cause side effects. However, not everyone who uses the contraceptive will experience side effects. In fact, most women tolerate it quite well. If Plan B side effects do occur, in most cases, they are minor and either require no treatment or are easily treated by you or your healthcare provider.
(This article covers many, but not all, of the possible side effects with Plan B. Your healthcare provider can discuss a more complete list of Plan B side effects with you.)

Common Side Effects of Plan B

In clinical studies for most medications, one group of people receives the actual medication, while another group is given a placebo (a "sugar pill" that does not contain any active ingredients). The side effects in both groups are carefully documented and compared. As a result, it is possible to see what side effects occur, how often they appear, and how they compare to the group not taking the medicine. However, it is not possible to use a placebo in clinical trials for contraceptives, as this would lead to many unintentional pregnancies. Therefore, some of the possible "side effects" of Plan B may not really be true side effects, but there is no way of knowing, because the studies did not use a placebo.
In studies, the most common Plan B side effects included:
  • Nausea -- in up to up to 23.1 percent of women
  • Abdominal pain (stomach pain) -- up to 17.6 percent
  • Fatigue -- up to 16.9 percent
  • Headaches -- up to 16.8 percent
  • A heavier menstrual period -- up to 13.8 percent
  • A lighter menstrual period -- up to 12.5 percent
  • Dizziness -- up to 11.2 percent
  • Breast tenderness -- up to 10.7 percent
  • Vomiting -- up to 5.6 percent
  • Diarrhea -- up to 5 percent.
Most women will get their period right on schedule after taking Plan B, although sometimes the drug can delay a period by a few days. If your period is more than a week late, you should take a pregnancy test to make sure you are not pregnant (after all, Plan B is not 100 percent effective).
Plan B One-Step (the newer version, taken as a single tablet) has similar side effects. In studies, the most commonly reported Plan B One-Step side effects included:
  • Heavy menstrual bleeding -- in up to 30.9 percent of women
  • Nausea -- up to 13.7 percent
  • Lower abdominal pain (stomach pain) -- up to 13.3 percent
  • Fatigue -- up to 13.3 percent
  • Headache -- up to 10.3 percent
  • Dizziness -- up to 9.6 percent
  • Breast tenderness -- up to 8.2 percent
  • A delayed menstrual period -- up to 4.6 percent.
Last reviewed by: Kristi Monson, PharmD
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