Side Effects of Plan B One-Step (levonorgestrel)

Plan B One-Step (levonorgestrel) is emergency contraception (commonly called the “morning after pill”) used as backup contraception to prevent pregnancy when taken within 72 hours after unprotected sex or when birth control fails.

Levonorgestrel is a progestin. Progestins are hormones used in many birth control pills. Although levonorgestrel and similar emergency contraception pills contain a higher dose of levonorgestrel than birth control pills, they work in a similar way to prevent pregnancy, mainly by stopping the release of an egg from the ovary.

Additionally, levonorgestrel also may prevent fertilization of an egg (the uniting of the sperm with the egg) or prevent the attachment (implantation) of a fertilized egg to the uterus (womb).

Emergency contraception pills do not work in women who are already pregnant and should not be taken during pregnancy. Most emergency contraception pills can be purchased over-the-counter or over-the-counter (OTC). Some age restrictions may apply.

Common side effects of Plan B One-Step include

• menstrual changes,
• nausea,
• lower stomach (abdominal) pain,
• tiredness,
• headache,
• dizziness,
• vomiting, and
• breast pain.

Drug interactions of Plan B One-Step include drugs or herbal products that increase the activity certain liver enzymes that breakdown drugs, which may reduce blood levels of levonorgestrel and the effectiveness of Plan B One-Step.

Emergency contraception pills such as Plan B One-Step will not work if you are already pregnant and should not be used during pregnancy. Plan B One-Step is thought to enter human milk after oral administration and should be used cautiously in breastfeeding mothers.

Side effects include:

• Menstrual changes
• Nausea
• Lower stomach (abdominal) pain
• Tiredness
• Headache
• Dizziness
• Vomiting
• Breast pain

Clinical Trial Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice.

A double-blind, controlled clinical trial in 1,955 evaluable women compared the efficacy and safety of Plan B (one 0.75 mg tablet of levonorgestrel taken within 72 hours of unprotected intercourse, and one tablet taken 12 hours later) to the Yuzpe regimen (two tablets each containing 0.25 mg levonorgestrel and 0.05 mg ethinyl estradiol, taken within 72 hours of intercourse, and two tablets taken 12 hours later).

The most common adverse events (>10%) in the clinical trial for women receiving Plan B included

• menstrual changes (26%),
• nausea (23%),
• abdominal pain (18%),
• fatigue (17%),
• headache (17%),
• dizziness (11%), and
• breast tenderness (11%).

Table 1 lists those adverse events that were reported in ≥5% of Plan B users.

Table 1: Adverse Events in ≥5% of Women, by % Frequency

Postmarketing Experience

The following adverse reactions have been identified during post-approval use of Plan B. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

Gastrointestinal Disorders

Abdominal Pain, Nausea, Vomiting

General Disorders and Administration Site Conditions

Fatigue

Nervous System Disorders

Dizziness, Headache

Reproductive System and Breast Disorders

Dysmenorrhea, Irregular Menstruation, Oligomenorrhea, Pelvic Pain

Drugs or herbal products that induce enzymes, including CYP3A4, that metabolize progestins may decrease the plasma concentrations of progestins, and may decrease the effectiveness of progestin-only pills. Some drugs or herbal products that may decrease the effectiveness of progestin-only pills include:

• barbiturates (including primidone)
• bosentan
• carbamazepine
• felbamate
• griseofulvin
• oxcarbazepine
• phenytoin
• rifampin
• St. John’s wort
• topiramate

Significant changes (increase or decrease) in the plasma levels of the progestin have been noted in some cases of co-administration with HIV protease inhibitors or with non-nucleoside reverse transcriptase inhibitors.

Concomitant administration of efavirenz has been found to reduce plasma levels of levonorgestrel (AUC) by around 50%, which may reduce the effectiveness of Plan B.

Consult the labeling of all concurrently used drugs to obtain further information about interactions with progestin-only pills or the potential for enzyme alterations.

Drug Abuse And Dependence

Levonorgestrel is not a controlled substance. There is no information about dependence associated with the use of Plan B.