Q: I’ve gained weight. I’ve heard that the contraceptive pill might not work as well as when I was thinner. Is there any truth to this?
A: Yes. And the heavier you are, the more likely it is that your oral contraceptive will be unreliable.
A recent study in the Journal of Obstetrics and Gynecology reported that the pill is less effective in suppressing ovulation in women whose Body Mass Index (BMI) is greater than 27.3.
The risk of pregnancy while on oral contraceptives was nearly 60 percent higher in women with a BMI of more than 27.3, as compared with their thinner cohorts, and nearly 70 percent higher in women with a BMI of more than 32. (For a woman of 5’4”, this translates into 159 pounds and 186 pounds, respectively.)
In other words, if 100 women with a BMI of more than 27.3 used the pill for a year, there would be 2 to 4 more pregnancies than if 100 thinner women did.
You can use your height and weight to calculate your BMI. Charts are available on the Internet at: or .
The reason for this ineffectiveness is quite simple: The hormones in oral contraceptives are fat-soluble and can become diluted when stored in excess fat. These hormones are then unavailable in levels high enough to signal the brain to suppress ovulation.
This dilution effect is most marked for very low-dose pills, those containing less than 25 micrograms of estrogen. (Most combined estrogen/progestin pills that are termed low-dose contain 30 to 35 micrograms of estrogen).
The contraceptive patch also is less effective in overweight women. In studies, it was only 92 percent effective in women weighing more than 198 pounds (compared to almost total effectiveness for thinner women).
So if you have gained a lot of weight — and do not plan to lose it anytime soon — you and your doctor should discuss using a different method of contraception, such as a barrier method or an intrauterine system.
There is also the possibility of taking a higher-dose pill (of which there are a few varieties available), but this must be done only on the advice of a doctor. This is because overweight people are already at higher risk for heart disease, clots and diabetes, and it may well be advisable not to take high-dose pills. What definitely should not be done is for women to take matters into their own hands and take, say, two pills instead of one.
If you know you will never want more children, tubal ligation (commonly known as “getting your tubes tied”) is an effective option (as is vasectomy for your male partner).
Dr. Reichman’s Bottom Line: Oral contraceptives perform less than perfectly if you are overweight, so consider losing weight or using other contraceptive options.
Dr. Judith Reichman, the “Today” show's medical contributor on women's health, has practiced obstetrics and gynecology for more than 20 years. You will find many answers to your questions in her latest book, "Slow Your Clock Down: The Complete Guide to a Healthy, Younger You," which is now available in paperback. It is published by William Morrow, a division of .
PLEASE NOTE: The information in this column should not be construed as providing specific medical advice, but rather to offer readers information to better understand their lives and health. It is not intended to provide an alternative to professional treatment or to replace the services of a physician.