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Discover the Most Effective and Safe Birth Control Options for Overweight Women

November 22, 2023

This article explores birth control safety for overweight women and guides on the best/most effective methods.

If you are overweight (weigh over 70kg) or have a BMI of over 26, you may wonder which birth control method is safest and most effective.

The benefits of using birth control are clear, whatever weight you are.

But for women of childbearing age, being overweight has additional risks during pregnancy, such as higher risks of spontaneous abortion, pre-eclampsia, gestational diabetes, shoulder dystocia and cesarean section.

Therefore, preventing unintended pregnancy is at least as important for obese women as for normal-weight women and those with chronic health conditions.

overweight lady looking at different birth control options

You’ve probably heard that birth control methods do not always work the same way in all women and that it is possible that your weight may affect their effectiveness.

Points to note:

Several authorities worldwide pool together research that drives their recommendations on birth control.

Primarily, we refer to guidelines from the UK Faculty of Sexual and Reproductive Health (FSRH) in this article but may draw from other scientific journals.


Finally, the data available on the specific effects of many methods on weight is limited (though improving); please note that many of the guidelines are based on studies for women with a BMI under 40, as there are no/few available studies, including women with a BMI over 40.

So, let’s look at the state of effectiveness and birth control safety for overweight women.

How Excess Weight Can Affect Drugs in the Body

First, how or why is your weight even an issue regarding birth control?

This speaks particularly to hormone-containing contraception methods, i.e., Progesterone and Oestrogen. 

Experts believe excess body weight may affect the effectiveness of hormonal birth control by changing how these drugs are absorbed, distributed, metabolised or cleared from the body.

If you’re overweight, your body’s physiology can differ slightly from someone with a normal weight range in a few ways.

For instance, your heart pumps out more blood each time it beats or the way your liver works. 

These differences may affect how drugs are absorbed, distributed, metabolised and eliminated.

Absorbing a drug

To proceed, let’s look at how the changes may affect the absorption of a drug after you take it.

After taking a drug by mouth, if you are overweight, you may absorb it better through your gut because of greater blood flow from the heart. However, if you get a drug via the skin or muscles, the absorption could be slower because of large fat deposits.

How drugs are carried in the blood

Next, having more fat cells can affect the proteins that hold or bind a drug from your blood.

This will determine how much of the drug can work effectively within the body.

Fat cells may also metabolise hormones in birth control, affecting their effectiveness.

Excessive weight and effect on drug clearance

Finally, could being overweight affect how the drug is cleared from your system – either delaying or speeding it up so you have more or less drug available?

So, these are possible reasons the effectiveness of a drug may be affected by your weight.

But now, let’s look at the effect of excess weight on certain hormonal birth control options.

Birth Control Options/Effectiveness

1. Intrauterine Device (IUD)

We begin with the IUD, which has a typical failure rate of 0.2 per 100 woman years. This means that out of 10,000 women using this method, 20 will fall pregnant in the first 12 months.

Since the contraceptive effect of IUDs happens mainly via local actions on the uterus, there is no reason to think that IUDs would be less effective in obese women than in women of normal weight.

There are some accounts of inserting the coil being more technically tricky in obese women and a concern that it may be expelled more easily afterwards.

Still, we need more studies that explore this issue reliably. 

Thus, because it is highly effective across the BMI spectrum, intrauterine contraception is an excellent choice for overweight or obese women wishing to delay or avoid pregnancy.

2. Contraceptive Implant

Next are the implants, another highly effective option with a typical failure rate of 0.05 per 100 woman years; in other words, out of 10,000 women using this method, 5 will fall pregnant within the first year. 

Implants contain the Progesterone hormone in either of 2 forms – Etonogestrel, ENG or Levonorgestrel, LNG. 

According to our data for the ENG implant, the hormone levels decline over time in overweight women compared to normal weight.

Still, generally, the decline does not go beyond a level that would prevent the suppression of ovulation.

That means that while the hormone levels are lower in overweight girls, it is still effective for birth control, and currently, the FSRH does not recommend changing the implant earlier than the recommended 3 years because a woman is obese or overweight. 

For the LNG implant, studies show no difference, and it is thought that body weight does not reduce the efficacy of this method for overweight ladies.

Caution: According to FSRH, data for those with BMI>40 is unavailable.

3. Depot (Progesterone) Shot

The Depo shot is a highly effective, reversible contraception that lasts approximately 3 months.

It is available as an injection into the muscle or just under the skin.

Its typical failure rate is 6 per 100 women years – hence, 600 women out of 10,000 will fall pregnant within the first year of use. 

Studies suggest that being overweight does not reduce the effectiveness of the Depo shot.

To use the depot shot in the muscle, longer needles may be necessary for overweight women to advance beyond the fat under the skin. 

An alternative progesterone injection (Norethisterone) is given every 8 weeks. A study showed no difference in the amount of the drug in the blood when taken by overweight and normal-weight women. 

4. Contraceptive Pill/Patch/Ring

The combined methods have both oestrogen and progesterone and a typical failure rate of 9 per 100 woman years – meaning 900 women out of 10,000 will fall pregnant in the first 12 months of use.

Let’s look at the different options specifically:

Combined Oral Contraceptive (COC)/Pill

Some studies found that overweight or obese women (BMI >25 kg/m2) were almost twice as likely to become pregnant while relying on COCs than their normal-weight peers.

Others found no difference. While the data conflict, the conclusion seems to be that pregnancy rates among overweight and obese women using COC seem to be similar to or slightly higher than rates among normal-weight women.

The large numbers of women included in some studies and the biological plausibility for altered PK suggest that COC may be less efficacious in obese women.

Patch 

The patch contains a similar combination of hormones to the combined pill.

Compared with oral pills in normal-weight women, the patch delivers a higher concentration of the hormones into the blood than the pill.

However, this is reduced slightly for overweight women due to a larger area and weight effects.

A number of studies show increased pregnancy rates in women over the weight of 90 kg using the patch, leading the authors to conclude that women in this weight category may be at increased risk of contraceptive failure with the patch.

Ring

The contraceptive vaginal ring provides a non-oral, nondaily contraceptive method for women interested in short-term birth control. 

It’s associated with lower systemic hormone exposure than the pill or patch.

We only have a few studies comparing normal weight to overweight women on the ring. Still, the few available suggest little difference in the ring’s effectiveness. 

5. Mini Pill (Progesterone Only Pill)

The mini pill, also known as progesterone only, has a typical failure rate of 9 per 100 women years; 900 women out of 10,000 will fall pregnant in the first 12 months of use.

The effectiveness of the minipill is not affected by body weight or BMI.

Thus, a double dose of the minipill is unnecessary if you are overweight or obese.

6. Emergency Pill/Morning After Pill (MAP)

The LNG MAP (Plan B, Take action, Post pill, Ipil, Postinor, Levonelle, etc.) effectively reduces pregnancy risk up to 72 hours after unprotected intercourse.

Alternatively, Ella (Ullipristate) pill is effective up to 5 days after unprotected intercourse.

Both work by delaying ovulation; if taken within 72 hours, the former prevents 50% of unplanned pregnancies. In contrast, the latter prevents 66% of them.

Weight does affect their effectiveness and, to a greater extent, with LNG than Ella MAP.

 Studies show that overweight ladies 4 times more likely to fall pregnant using the LNG pill.

At the same time, pregnancy is twice as likely on the Ella MAP.

Pictogram on blood clot estimated risks - birth control safety for overweight women

Hormonal Birth Control Safety for Overweight Women

Okay, now we’ve looked at these 6 methods; let’s change tack and look at birth control safety for overweight women.

There is always a possibility of unplanned pregnancy with any birth control method. (No method is 100% effective).

For some birth control methods, overweight women may be at greater risk of unplanned pregnancy and complications. 

Hormonal contraception is safe for overweight or obese women without other contraindicating health conditions.

Our guidelines advise that there are no safety concerns with using any progestin-only contraceptive methods in obese women.

This includes pills, injectables, implants and intrauterine contraception.

Even the combined birth control methods are relatively safe* if you are overweight.

The biggest safety concern with using combined birth control when overweight is developing a blood clot within one of your arteries or veins.

Overweight women are twice more likely than normal-weight women to develop blood clots.

Overweight women on combined birth control are more likely to develop clots than overweight women who are not. (This refers to any combined method – pill, patch or ring.)

But let’s back up and place this in context. 

The risk of developing a blood clot in women of childbearing age is relatively small.

There is a much higher risk of developing a blood clot when pregnant or within the immediate postpartum period.

Thus, an obese woman on the combined method, without any other medical condition, is actually safer from blood clots than an obese, pregnant woman.

*Progesterone-only methods are preferable for overweight women to avoid the risks of blood clots.

Which is the Best Method if you are Overweight?

So, if you are overweight and wondering what method is best to use given the safety and effectiveness issues mentioned here – don’t be worried.

The choice of method is very individual, and the presence of many options is a plus rather than a cause for uncertainty.

Concerning safety, as long as you have no other risk factors, you can use any of these methods, though, as we note above, they have different safety profiles.

Overweight ladies should first choose those with the lowest risk.

Regarding effectiveness, you can also use any of these methods depending on your health background, preference and availability.

Also, recall that using any of these methods is better than using none when preventing unplanned pregnancy.

With that said the research does indicate the patch to be less reliable among the regular short-term options, so you should go for longer-acting methods like the IUD, implant or Depo shot.

You can use the combined or mini pill or ring if that is your preferred option, but bear in mind reports of slightly less effectiveness with the combined pill and its higher risk of blood clots.

If you go with the patch, consider using a condom to boost your chances of protection.

What is the most Effective Emergency Birth Control Method for Overweight Women?

Suppose you are over 70kg or have a BMI of 26 then according to the UK’s Leading authority on reproductive health, the FSRH, the most effective method is the Copper IUD inserted within 5 days of UPSI if it is appropriate for you.

If that is not appropriate or acceptable, then the Ella (Ulipristal) single-dose pill is an option you can use. 

Finally, the last option is the LNG MAP we commonly know as Levonelle, Take Action, plan B Post Pill, and so on.

Commonly, it is thought that the standard dose of these pills is not effective in women over 70kg or a BMI >26. Thus, the recommendation is to double the dose of the LNG pills if you are overweight and are taking them. 

But is this double dose guaranteed to work?

Recent studies suggest even the double-dose LNG pill may not effectively prevent pregnancy in overweight women, but we still need more work to confirm this.

Meanwhile, if you are overweight and choose the LNG pill, the double dose is safe and a better option than nothing.

We hope this answers your questions about birth control safety for overweight women.

 If you need further clarification, please reach us here.

More Reading

Editing by AskAwayHealth Team

Disclaimer

All AskAwayHealth articles are written by practising Medical Practitioners to help promote quality healthcare. 

The advice in our material does not replace a qualified healthcare practitioner’s management of your specific condition.
Please get in touch with a health practitioner
 to discuss your condition, or reach us directly here.

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