Does Body Weight Affect Emergency Contraception?
Quick Answer
Research suggests levonorgestrel may be less effective in people with higher body weight (BMI over 25-30), though it still provides some protection. Ulipristal acetate appears to maintain effectiveness across a wider weight range. A copper IUD is the most effective option regardless of weight.
What Research Shows
Studies have found:
- Levonorgestrel (Postinor) may be less effective in people with BMI over 25-30
- Ulipristal acetate (Mifestad) maintains effectiveness across a wider weight range
- Copper IUD is the most effective option regardless of weight
However, some effectiveness is still better than no protection.
Levonorgestrel (Postinor) and Weight
Research suggests:
- Effectiveness may decrease at higher body weights
- Some studies suggest reduced effectiveness starting at 165 lbs (75 kg)
- The medication may be metabolized differently at higher weights
Important: Postinor still provides some protection at any weight. Taking it is better than not taking it.
Ulipristal Acetate (Mifestad) and Weight
Mifestad appears to perform better across weight ranges:
- Maintains effectiveness at higher body weights
- Studies show consistent results across BMI categories
- May be the preferred pill option if weight is a concern
Recommendation: If you're concerned about weight and effectiveness, Mifestad is the better pill choice.
Best Options by Weight
Based on current research:
| Weight/BMI Range | Recommended Option | Notes |
|---|---|---|
| Under 165 lbs / BMI <25 | Postinor or Mifestad | Both are highly effective |
| 165-195 lbs / BMI 25-30 | Mifestad preferred | Better data on effectiveness |
| Over 195 lbs / BMI >30 | Mifestad or Copper IUD | IUD is most reliable option |
Copper IUD: The Weight-Neutral Option
The copper IUD is over 99% effective regardless of body weight because:
- It works locally in the uterus
- Effectiveness doesn't depend on medication absorption or metabolism
- Can be inserted up to 5 days after unprotected sex
- Provides ongoing contraception for up to 10-12 years
Contact us for a referral to a provider who can insert a copper IUD.
The Bottom Line
Regardless of your weight:
- Some protection is better than none
- Don't skip EC because of weight concerns
- Mifestad is the better pill choice if weight is a concern
- Copper IUD is the most effective option at any weight
Get the right EC option for you.
View OptionsFrequently Asked Questions
No. Doubling the dose is not recommended and hasn't been shown to improve effectiveness. Instead, choose Mifestad or consider a copper IUD if weight is a concern.
No. EC still provides some protection at any weight. Reduced effectiveness doesn't mean zero effectiveness. Always take EC if needed - some protection is better than none.
Medications are absorbed and metabolized differently based on body composition. Levonorgestrel (Postinor) concentrations may be lower at higher body weights. The copper IUD works locally, so weight doesn't affect it.
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