Emergency contraceptive pills (ECPs), often called 'morning-after pills,' are a safe and effective way to prevent pregnancy after unprotected intercourse or contraceptive failure [1.7.5]. They primarily work by delaying or inhibiting ovulation [1.3.2]. However, they are not a one-size-fits-all solution. Understanding the specific circumstances and medical conditions that preclude their use is vital for personal health and ensuring the medication works as intended. According to the World Health Organization, there are no absolute medical contraindications for emergency contraception, except for a confirmed pregnancy, but several factors can influence the decision [1.3.3, 1.9.2].
Absolute Reasons Not to Take Emergency Pills
There are a few clear-cut situations where taking an ECP is not appropriate. These are considered absolute contraindications, meaning the pill should not be used under these circumstances.
Confirmed or Suspected Pregnancy
Emergency contraceptive pills are not effective if you are already pregnant [1.2.2, 1.3.4]. ECPs work to prevent pregnancy; they do not interrupt an established one and are not abortion pills [1.7.3, 1.8.4]. If you know or suspect you are pregnant, you should not take an ECP [1.2.5]. While studies on levonorgestrel show it does not harm a developing fetus if taken inadvertently, the effects of ulipristal acetate on an existing pregnancy are unknown [1.2.3, 1.2.6].
Known Allergy
You should not take an emergency pill if you have a known allergy or hypersensitivity to any of its active ingredients (levonorgestrel or ulipristal acetate) or any of the inactive components in the tablet [1.2.2, 1.2.3, 1.5.2]. An allergic reaction can be serious, and alternative EC methods should be considered.
Unexplained Vaginal Bleeding
If you are experiencing abnormal or unexplained vaginal bleeding, it is important to consult a healthcare provider before using an emergency pill [1.2.2, 1.2.5]. This type of bleeding could be a symptom of an underlying medical condition that needs to be diagnosed and addressed.
Important Considerations & Relative Contraindications
Beyond absolute contraindications, several factors require careful consideration, as they can impact the pill's effectiveness or safety.
Time Since Unprotected Intercourse
ECPs have a limited window of effectiveness.
- Levonorgestrel pills (e.g., Plan B One-Step, My Way) are most effective when taken as soon as possible, ideally within 72 hours (3 days) of unprotected sex [1.7.3, 1.7.4]. Their effectiveness decreases with time [1.7.3].
- Ulipristal acetate (ella) can be taken up to 120 hours (5 days) after unprotected sex and maintains its effectiveness throughout this window [1.2.1, 1.7.4]. Taking the pill after this window has closed is not recommended as it is unlikely to be effective [1.2.1].
Drug Interactions
Certain medications and herbal supplements can reduce the effectiveness of ECPs by inducing liver enzymes that metabolize the hormones faster. These include:
- The herbal remedy St. John's Wort [1.2.3, 1.6.3]
- Certain antibiotics like rifampicin and rifabutin [1.6.2, 1.6.6]
- Some medications used to treat epilepsy (e.g., phenobarbital, phenytoin, carbamazepine), HIV, or tuberculosis [1.6.4, 1.6.6] If you are taking any of these medications, ulipristal acetate (ella) is not advised, and a double dose of levonorgestrel may be recommended by a healthcare provider [1.3.1]. The copper IUD is an effective alternative that is not affected by these medications [1.5.6].
Medical Conditions
While most individuals can safely use ECPs, those with certain pre-existing conditions should consult a doctor.
- Severe Liver Disease: Individuals with severe liver disease or active acute porphyria should not use levonorgestrel or ulipristal acetate [1.3.1, 1.4.2, 1.5.3].
- Severe Asthma: Ulipristal acetate is not recommended for women with severe asthma that is poorly controlled with oral glucocorticoids [1.5.2].
- Breastfeeding: If you take ulipristal acetate while breastfeeding, it is advised to pump and discard breast milk for a week after taking the pill [1.3.3]. Levonorgestrel is considered safe for use during breastfeeding as only a small amount passes into the milk with no identified adverse effects on the infant [1.3.3, 1.4.2].
Body Weight and BMI
Research suggests that the effectiveness of oral ECPs may be reduced for individuals who are overweight or obese [1.2.3].
- Levonorgestrel may be less effective in people weighing over 165 pounds or with a BMI over 25 [1.7.1, 1.7.2].
- Ulipristal acetate (ella) is considered more effective than levonorgestrel for people with a higher BMI but may lose some effectiveness in those weighing over 195 pounds [1.7.1, 1.8.1]. The copper IUD is the most effective form of emergency contraception and its effectiveness is not impacted by weight [1.7.2].
| Feature | Levonorgestrel (e.g., Plan B) | Ulipristal Acetate (ella) |
|---|---|---|
| Effective Window | Up to 72 hours (3 days) [1.2.3] | Up to 120 hours (5 days) [1.2.3] |
| Prescription needed? | No, available over-the-counter [1.2.1] | Yes, prescription required [1.2.1] |
| Weight Considerations | May be less effective if BMI > 25 or weight > 165 lbs [1.7.2, 1.8.1] | More effective than levonorgestrel at higher BMIs, but may be less effective if weight > 195 lbs [1.7.1, 1.8.1] |
| Interaction with Hormonal Birth Control | Can start or resume hormonal birth control immediately [1.8.1] | May reduce effectiveness of hormonal contraception; a barrier method is needed for 14 days after use [1.3.1, 1.5.4] |
| Use While Breastfeeding | Considered safe [1.3.3] | Not recommended; pump and discard milk for one week [1.3.3, 1.5.3] |
Conclusion
Emergency pills are a critical tool for preventing unintended pregnancy, but they are not always the right choice. Knowing when not to take emergency pills—due to confirmed pregnancy, allergies, the time elapsed since intercourse, interactions with other drugs, or certain medical conditions—is essential for safe and effective use. If oral ECPs are not a suitable option, the copper IUD stands as the most effective alternative, unaffected by weight or most medications [1.7.2, 1.7.5]. Always consult with a healthcare professional or pharmacist if you have doubts about your eligibility or which method is best for your specific situation.
For more information, you can visit the World Health Organization's page on Emergency Contraception.
