Emergency contraception, commonly known as Plan B, prevents pregnancy after unprotected sexual intercourse or contraceptive failure. This medication contains a high single dose of the synthetic hormone levonorgestrel, typically 1.5 milligrams (mg). It is intended as a backup method, not a regular form of birth control. Taking two 1.5 mg pills for a total of 3.0 mg introduces a significantly larger hormonal load than is medically necessary, raising questions about safety and effectiveness.
The Standard Mechanism of Levonorgestrel
The primary action of levonorgestrel emergency contraception is to prevent or delay ovulation. This high dose of the progestin hormone suppresses the luteinizing hormone (LH) surge, which triggers ovulation. By inhibiting this surge, the drug ensures no egg is available for fertilization. The standard 1.5 mg dose is most effective when taken as soon as possible, ideally within 72 hours of unprotected sex, though it may offer protection up to 120 hours. Effectiveness significantly decreases once ovulation has already occurred. Levonorgestrel does not prevent implantation or terminate an existing pregnancy.
Immediate Physical Effects of Doubling the Dose
Taking two doses (3.0 mg total) is not considered toxic or life-threatening for a person without an underlying medical condition. The main consequence of this elevated hormonal intake is the exaggeration of common, short-term side effects like nausea, headache, fatigue, and dizziness.
A person is more likely to experience severe nausea and vomiting with the 3.0 mg dose. Vomiting is a particular concern because if it occurs within two hours of taking the pill, the medication may not have been fully absorbed, necessitating a replacement dose. Other amplified physical effects include more pronounced breast tenderness and greater fatigue or general malaise.
The body is suddenly saturated with a higher concentration of the synthetic progestin, leading to a more intense, temporary systemic reaction. These amplified side effects typically resolve within 24 to 48 hours. The double dose is sometimes intentionally prescribed by a healthcare provider for individuals taking certain medications that speed up levonorgestrel metabolism or for those with a higher body mass index (BMI).
Efficacy and Menstrual Cycle Disruption
For the general user, taking two doses of levonorgestrel does not significantly increase effectiveness beyond the high success rate of the single, timely dose. The standard 1.5 mg dose is generally sufficient to achieve the necessary hormonal disruption to delay ovulation. Research indicates that for most people, increasing the dose does not boost efficacy.
The most common negative outcome associated with the high hormonal load is severe disruption to the subsequent menstrual cycle. The excess hormone can cause unscheduled bleeding or spotting between the time the pill is taken and the next expected period. This intermenstrual bleeding can be heavier or last longer than the spotting typically experienced with a single dose.
The next expected menstrual period is frequently affected, often arriving earlier or later than usual, sometimes by up to a week. The flow itself may be heavier or lighter than normal. This substantial hormonal interference can make the cycle immediately following the double dose highly irregular.
When Professional Medical Advice is Necessary
While the side effects of a double dose are usually temporary, certain symptoms warrant immediate contact with a healthcare provider. If severe vomiting occurs within two hours of taking the second pill, seek medical advice to determine if a replacement dose is needed. Persistent or severe side effects lasting more than 48 hours also require professional guidance.
A person should contact a doctor if their period is delayed by more than one week past the expected date, as this may indicate the need for a pregnancy test. Severe lower abdominal pain, particularly three to five weeks after taking the medication, requires immediate medical attention. This intense pain could signal an ectopic pregnancy, where a fertilized egg implants outside the uterus.