Concerns are spreading among women that using obesity drugs such as Mounjaro alongside oral contraceptives can reduce the pill's effectiveness and lead to unintended pregnancies. [Getty Images]
Concerns are spreading among women that using obesity drugs such as Mounjaro alongside oral contraceptives can reduce the pill's effectiveness and lead to unintended pregnancies. [Getty Images]

On the pill but five weeks pregnant — Mounjaro use under suspicion

Obesity drugs slow contraceptive absorption, may restore ovulation

Fetal safety risks flagged if obesity drugs taken during pregnancy

Suspected cases are emerging in South Korea of women becoming pregnant while taking oral contraceptives alongside the obesity drug Mounjaro. As similar cases multiply, the term "Mounjaro baby" has entered common usage among women. Medically, obesity drugs can reduce the absorption rate of oral contraceptives, weakening their effectiveness — meaning women who rely on the pill alone while using these drugs risk unintended pregnancy.

A 36-year-old woman identified only as A had every reason to believe pregnancy was out of the question. She weighed 103 kilograms at 165 centimeters, had a long history of taking oral contraceptives to manage polycystic ovary syndrome, and rarely saw her husband. She had effectively ruled out the possibility of conceiving. "I'd heard a lot about 'Mounjaro babies,' but I never thought it would happen to me," she said.

About three months after she began taking Mounjaro for health reasons, she learned she was five weeks pregnant. Her doctor told her the drug may have made conception possible. "I was too complacent about being on the pill and never even considered the possibility of getting pregnant," she said in an interview. "This baby came without any preparation, but it happened even under difficult circumstances — I want to raise this child well."

Warnings have been mounting that GLP-1-based obesity drugs such as Mounjaro and Wegovy can affect women's fertility. Last year, the UK's Medicines and Healthcare products Regulatory Agency (MHRA) urged women using GLP-1-based medications to exercise caution regarding pregnancy and contraception. At the time, the MHRA had received more than 40 reports of unintended pregnancies among users of such drugs.

Overseas, accounts of unexpected pregnancies during GLP-1-based obesity drug use have been piling up. Terms such as "Mounjaro baby," "Wegovy baby" and "Saxenda baby" emerged as these cases grew in number. As the use of obesity drugs including Wegovy and Mounjaro has rapidly expanded in South Korea, similar experiences have begun circulating on social media.

Jo Byeong-gu, administrative director of the Korean Society of Obstetrics and Gynecology, said pharmacokinetic research showed that co-administering tirzepatide with oral contraceptives reduced the pill's maximum blood concentration by up to 66 percent. "It is recommended that women use additional contraceptive methods such as condoms, or non-oral contraception, for four weeks after starting Mounjaro or increasing the dose," he said.

A pharmacist said younger women today are less resistant to oral contraceptives than previous generations and tend to take charge of their own contraceptive decisions, driving an increase in pill use. "Many women also take oral contraceptives not just for birth control but to treat conditions such as polycystic ovary syndrome or acne," the pharmacist added.

Gynecology clinics are also seeing patients suspected of having experienced contraceptive failure linked to obesity drug use. Another gynecologist said that since around last year, the first question asked of patients who come in after a contraceptive failure is whether they have been using an obesity drug. "If they say yes, the obesity drug is treated as one likely cause," the doctor said.

Pharmacist B, who works at a pharmaceutical company, addressed the heightened pregnancy risk following obesity drug use. "The product information for obesity drugs including Mounjaro explicitly states that fetal safety during pregnancy has not been established," B said. "Simply put, there is a possibility that problems could arise, and the pharmaceutical company is saying it will not take responsibility in such situations. The phrase 'safety has not been established' should not be taken lightly as merely meaning 'we don't know yet.'"


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hong@heraldcorp.com