What is the Plan B (levonorgestrel) pill?

What is Plan B?

Plan B is an emergency contraceptive pill containing levonorgestrel (1.5 mg) that prevents pregnancy after unprotected intercourse or contraceptive failure by primarily delaying or inhibiting ovulation. 1, 2

Mechanism of Action

• Plan B works by stopping or delaying the release of an egg from the ovary when taken before ovulation occurs 2
• The medication may also affect sperm migration in the female reproductive tract 3
• Plan B does NOT work if you are already pregnant and will not affect an existing pregnancy 2
• Research demonstrates that Plan B has little or no effect on post-ovulation events (fertilization or implantation), with all observed pregnancies occurring when the medication was taken after ovulation had already occurred 4

When and How to Use It

• Take Plan B as soon as possible within 72 hours (3 days) after unprotected intercourse, though it can be effective up to 120 hours (5 days) 1, 5, 2
• The sooner you take it, the better it works—effectiveness decreases significantly with time 5, 2
• Plan B is available as a single 1.5 mg tablet taken all at once 1, 2
• If using the older two-dose formulation (0.75 mg each), both doses can be taken simultaneously without reducing effectiveness 1, 5

Effectiveness

• Plan B reduces the risk of pregnancy by approximately 75-85%, preventing about 7 out of 8 expected pregnancies 2, 6, 7
• Treatment initiated within 72 hours provides the highest effectiveness 5
• Pregnancy rates remain low when administered within 4 days but increase at 4-5 days after intercourse 1, 5
• Plan B may be less effective in women with higher body weight or obesity, though it should still be offered 1, 5

What Plan B Is NOT

• Plan B is NOT a regular birth control method—it is less effective than routine contraception and should only be used as emergency backup 2
• It does NOT protect against HIV or other sexually transmitted diseases 2
• It is NOT an abortion pill and will not terminate an existing pregnancy 2

After Taking Plan B

• You can start any regular contraceptive method immediately after taking Plan B 1, 5
• Use barrier contraception or abstain from sex for 7 days after taking Plan B if starting hormonal contraception 1
• If vomiting occurs within 2 hours of taking the medication, contact a healthcare provider about repeating the dose 2
• Expect your next period at the usual time or within one week; if your period is more than one week late, take a pregnancy test 2

Common Side Effects

• Changes in menstrual bleeding pattern (heavier, lighter, early, or late period) 2
• Nausea (though Plan B causes less nausea than combined estrogen-progestin emergency contraception) 5
• Lower abdominal pain, tiredness, headache, dizziness, and breast tenderness 2
• Severe abdominal pain may indicate ectopic pregnancy and requires immediate medical attention 2

Availability and Access

• Plan B is available over-the-counter without a prescription for individuals 17 years and older in the United States 7, 8
• Advance provision of Plan B may be beneficial so it is available when needed and can be taken as soon as possible 1, 5
• Studies show advance provision increases use of emergency contraception without adversely affecting regular contraceptive behavior 5, 3

Important Drug Interactions

• Medications including efavirenz (HIV medication), rifampin (tuberculosis treatment), or seizure medications may reduce Plan B's effectiveness 2
• Your doctor may prescribe an alternative form of emergency contraception (such as ulipristal acetate or copper IUD) if you take these medications 2

Critical Pitfall to Avoid

Many women do not know emergency contraception is available and fail to ask for it 6. Healthcare providers should proactively discuss emergency contraception during routine gynecologic visits, as women counseled about emergency contraception are 11 times more likely to use it when needed 7.