3 Reproductive Health Medications Affected by Women's Weight

Overweight or obese women may experience unique difficulties with their reproductive health medications.

Data from the US Centers for Disease Control and Prevention indicate that more than one-third of Americans are currently obese, and a report published in the American Journal of Preventive Medicine projects that 50% of the US population will be obese by 2030.

Amid this growth in obesity rates, the American Society of Health-System Pharmacists recently published a guide to help pharmacists determine optimal medication dosing in obese patients.

“It is essential that clinicians have a thorough understanding of the complexities involved in making dosing decisions for obese patients,” stated guide co-editor Brandon R. Shank, PharmD, BCOP. “It is our hope that this guide depicts the existing literature in a way that allows practitioners to apply literature to real-life patient scenarios.”

Of note, the following 3 reproductive health medications may not work as indicated in women who are obese or overweight.

1. Fertility Drugs

Overweight and obese women tend to have poorer outcomes when taking fertility drugs.

One study published in the Journal of Clinical Endocrinology and Metabolism found that gonadotrophin-releasing hormone (GnRH) antagonists leave the bodies of overweight or obese women too quickly, which increases the risk that “the brain will signal the body to discharge the eggs from the ovaries too early," stated study author Nanette Santoro, MD, of the University of Colorado at Denver.

"We were surprised to find obese women were more likely to experience this, and it may be one reason why overweight and obese women have a higher rate of unsuccessful [in vitro fertilization] cycles than normal-weight women do,” she hypothesized. "Our findings indicate obese women may need a different or increased dosing regimen to improve fertility treatment outcomes.”

Additionally, fertility drugs may not work in overweight or obese women because of polycystic ovarian syndrome, which can cause a failure to ovulate.

Pharmacists can play a role in counseling these patients to make lifestyle changes to lose weight, as evidence suggests that as little as 5% of bodyweight loss can help improve fertility outcomes.

2. Birth Control Pills

The effectiveness of oral contraceptive pills has been linked to a woman’s weight.

Studies have shown that obesity causes pharmacokinetic alterations in contraceptive steroid hormones. Particularly, research published in Expert Review of Clinical Pharmacology showed that it might take twice as long for oral contraceptives to reach optimal levels in obese women.

Beyond effectiveness, oral contraception increases the risk of venous thromboembolism (VTE), and obese women already have an elevated VTE risk.

In addition to providing weight-loss counseling, pharmacists can offer patients information on non-oral contraceptives such as copper- or levonorgestrel-releasing intrauterine devices.

3. Emergency Contraception

Emergency contraception can be taken within a few days of unprotected sex to help women avoid becoming pregnant. Efficacy of the morning-after pill is as high as 95% when taken within 24 hours, and up to 89% within 72 hours.

However, a study published in the journal Contraception found that the risk of pregnancy was more than 3 times greater for obese women than women with a normal body mass index.

Beyond weight-loss counseling, pharmacists can recommend the copper T intrauterine device, which the Kaiser Family Foundation says is a reliable alternative emergency contraception for any woman when inserted within 5 days of unprotected intercourse.