Plan B, also known as the morning after pill, is an emergency contraceptive that can prevent pregnancy after unprotected sex or birth control failure. The recommended dose is one Plan B pill within 72 hours of unprotected intercourse. However, some women wonder if taking two pills is better, especially if they have a higher body weight.
How does Plan B work?
Plan B contains a high dose of levonorgestrel, a synthetic progestin hormone that prevents ovulation, fertilization, and implantation. When taken as directed, it is up to 89% effective at preventing pregnancy. Here’s a quick overview of how it works:
- Prevents or delays ovulation – It stops the ovary from releasing an egg.
- Alters tubal transport of sperm and egg – It slows down the egg and sperm so they are less likely to meet.
- Prevents fertilization – If ovulation does occur, it prevents fertilization.
- May prevent implantation – It may prevent a fertilized egg from implanting in the uterus.
The sooner it is taken, the more effective it is. Taking it within 24 hours of unprotected sex is best. Effectiveness declines the longer you wait.
Does body weight impact Plan B effectiveness?
Some research indicates that Plan B may be less effective in women with higher body weight or obesity. This is likely because the standard dose doesn’t provide enough of the active ingredient to effectively prevent ovulation and fertilization. A few key points:
- Plan B works primarily by preventing or delaying ovulation. To do this, it needs to reach certain blood levels of levonorgestrel.
- Heavier women have lower blood levels of levonorgestrel after taking Plan B. This may prevent it from working properly.
- Studies found the drug wasn’t as effective in women over 165 pounds. It failed more often in women over 175 pounds.
- Obese women were found to have 4 times higher risk of pregnancy after Plan B failure compared to women of normal weight.
The bottom line is that Plan B may not reliably prevent pregnancy in heavier women above 165 pounds or with obesity. This is because less of the drug is absorbed compared to women with lower body weights.
Is taking a double dose better?
Some women wonder if taking two Plan B pills at once (double dose) is a better option if they are overweight. Here are the pros and cons of this approach:
Potential benefits
- Increases blood levels of levonorgestrel – Doubling the dose provides more of the active drug.
- Improves effectiveness – May prevent ovulation and fertilization more reliably.
- Already shown safe – Taking two pills at once has not shown serious side effects.
Potential risks and considerations
- Not proven more effective – While it makes sense, there’s limited data on outcomes.
- Increased side effects – Nausea, dizziness, headache may be worse.
- Still may not work – Effectiveness is not guaranteed at any weight.
- Not approved dosing – Taking two pills is considered “off-label” use.
- Higher cost – You will need to buy two boxes of Plan B.
There isn’t strong evidence that doubling the dose works better due to a lack of scientific studies. However, it can be considered based on the rationale that more levonorgestrel should increase blood levels. Speak to your pharmacist or doctor for advice specific to your situation.
What does the research say?
Here is a summary of key scientific studies looking at Plan B and body weight:
Study 1
- Published 2010 in Contraception journal
- Looked at Plan B effectiveness in women weighing 165-176 lbs
- Found 2-fold higher risk of pregnancy compared to women under 165 lbs
- Suggested less drug is absorbed in heavier women
Study 2
- Published 2011 in Obstetrics & Gynecology journal
- Examined pregnancy rates after Plan B failure in obese women
- Obese women had 4 times higher risk of pregnancy than normal weight women
- Indicated Plan B less effective in women with obesity
Study 3
- Published 2013 in Contraception journal
- Looked at blood levels of Plan B in obese women
- Found significantly lower drug levels compared to normal weight women
- Concluded less drug absorbed into the bloodstream
Study 4
- Published 2016 in Contraception journal
- Gave obese women either 1 or 2 Plan B pills
- Double dose achieved higher blood levels of drug
- No difference in side effects between groups
In summary, multiple studies show that Plan B appears less effective in overweight and obese women. Taking two pills achieves higher drug levels in the blood without increasing side effects. However, there’s limited evidence on whether a double dose actually improves effectiveness.
What are the alternatives?
If you are concerned about Plan B working properly due to your weight, there are a few alternatives to consider:
Ella (ulipristal)
- Another emergency contraceptive pill
- Contains ulipristal instead of levonorgestrel
- Can be taken up to 5 days (120 hours) after sex
- May work better for overweight women
- Requires a prescription
Copper IUD
- Non-hormonal emergency contraception
- Can be inserted up to 5 days after unprotected sex
- Over 99% effective in any size woman
- Provides ongoing birth control
- Requires placement by healthcare provider
Double dose of traditional birth control pills
- Taking 4+ birth control pills can prevent pregnancy
- Contains higher levels of hormones
- Must be certain progesterone-only formulations
- Vomiting is a possible side effect
The copper IUD is arguably the most effective option for overweight women. Ella is also specifically developed for heavier women. Talk to your doctor about the best emergency contraception choice based on your BMI.
Tips for Plan B success
To give Plan B the best chance of working properly, here are some tips if you have a higher body weight:
- Take it ASAP – Don’t wait until day 3, take it immediately after unprotected sex.
- Consider 2 pills – Discuss doubling dose with your pharmacist or provider.
- Get a prescription for Ella – It may work better for women over 165 lbs.
- Use backup protection – Use condoms for 7 days after taking it.
- Watch for periods – Take a pregnancy test if your period is late.
- See your doctor – Follow up to discuss your options.
While Plan B may be less reliable for overweight women, there are steps you can take to maximize its effectiveness. Consider a double dose or alternative emergency contraception as well.
Key Takeaways
- Plan B may be less effective for women over 165 pounds or with obesity.
- Heavier women absorb less of the active drug levonorgestrel.
- Taking a double dose can increase blood levels of the drug.
- There’s limited evidence on whether 2 pills improves efficacy.
- Alternatives are the Ella pill, copper IUD, or extra birth control pills.
- Take Plan B ASAP, use backup protection, and follow up with your doctor.
The Bottom Line
Research indicates Plan B may not work as well to prevent pregnancy in overweight and obese women compared to those with lower body weight. This seems to be because less of the active ingredient levonorgestrel gets absorbed into the body. While taking a double dose is reasonable, the data is limited on whether this improves effectiveness. Alternatives like Ella, a copper IUD, or extra birth control pills can be discussed with your healthcare provider. If you do take Plan B and have a higher weight, follow up closely and use backup protection to be safe.
