Can Tirzepatide Make Birth Control Pills Less Effective?
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Popular drugs used to treat type 2 diabetes and obesity can have unintended side effects.
One, tirzepatide — sold under the brand name Mounjaro — carries a warning specifically about birth control pills, stating that the medication could make them less effective.
The U.S. Food and Drug Administration (FDA) warning recommends people using oral contraceptives either switch to another form of birth control or use a barrier method for four weeks after starting the medication, as well as four weeks after each dose increase.
But there is still a lot we don’t know about how some drugs used for weight loss may reduce the effects of birth control pills, and why tirzepatide is the only one of these drugs that carries a warning specifically tied to birth control.
“There are a lot of unknowns and the data we have can answer some questions but not all,” says says Beverly Tchang, MD, an endocrinologist at Weill Cornell Medicine’s Iris Cantor Women’s Health Center in New York.
Can Weight Loss Drugs Affect How Birth Control Pills Are Absorbed?
Of the popular weight loss drugs tirzepatide, Ozempic, and Wegovy, Wegovy is the only one actually approved by the FDA specifically for weight loss. The other two are approved for managing type 2 diabetes, but are commonly prescribed off label for weight loss.
The drugs fall into categories of medications — dual agonist (tirzepitide or Mounjaro) and semaglutide (Wegovy and Ozempic) — that work in similar but not identical ways. The medications all stimulate certain hormones associated with appetite and feeling full. The body naturally produces these hormones for a short time after a person eats, but by introducing them artificially with these medications, food moves more slowly through the body and keeps people feeling full, longer.
Theoretically, this could affect how oral medications are absorbed. With birth control pills, the concern is not enough of the hormones that stop ovulation, and therefore prevent pregnancy, will be absorbed, making the contraceptives less effective. But so far, no studies have proven whether this is the case.
According to Sarah McBane, PharmD, associate dean of pharmacy education at the University of California in Irvine, who specializes in women’s health, the contraceptive warning specifically for tirzepatide may be because the medication is a dual agonist, meaning it acts on two gut hormones: glucagon-like peptide (GLP) and glucose-dependent insulinotropic polypeptide (GIP). Semaglutide medications only act on one, GLP.
Whether the impact these drugs have on these hormones affects how oral medications are absorbed is still not clear. However, they do all carry warnings about oral medications in general as a precaution.
“The prescribing information for all of these medications states that there is the potential to affect the absorption and efficacy of oral medications,” says Dr. McBane, adding that at least one study has shown that semaglutide does not significantly impact blood levels of the hormones in birth control pills.
The older study, published in 2015 in the Journal of Clinical Pharmacology, included 43 women taking both semaglutide and combined oral contraceptives. The researchers measured their hormones eight days before they started taking semaglutide and 13 weeks after they began the drug. At the end of the 13 weeks, when people were taking 1 milligram of semaglutide per week, the researchers did not measure any drops in ethinylestradiol or levonorgestrel, the two hormones used in the birth control pills.
Birth control pill interaction warnings are not listed on Wegovy or Ozempic’s labels. However, “they did not measure these levels during dose escalation, which is how the manufacturer of Mounjaro assessed medication interaction,” says Dr. Tchang
Eli Lilly, the maker of Mounjaro, completed a human clinical trial last year that specifically looked at the drug’s impact on birth control pills at different stages of escalation — when a person’s dose increases — but the results of the trial have not yet been released. Right now, the data they have on how the drug may impact oral contraceptives is slim, but is listed on the drug’s label to be safe.
Each company measured their drugs’ impact on birth control pills in different ways, meaning they can only make recommendations based on the data they have, which is different. Tchang notes that people have to be on these medications for about four weeks before the medicines have their full effects, a concept called steady state.
Eli Lilly measured the potential effect on birth control pills before this steady state, while Novo Nordisk, which makes both Wegovy and Ozempic, measured the same effects after. Both companies could only make recommendations on the data they have, which did not measure the same thing.
“We’re working with incomplete information,” Tchang says. “That’s potentially why we have two different answers to the same question.”
Tchang notes that the medications do function in slightly different ways, which could also be a factor in why one carries a warning for birth control pill efficacy and the others do not.
Still, most of her patients believe for them, the benefits of weight loss medication outweigh any potential risks. “Every doctor and patient needs to have an in-depth conversation about all of the nuances of risk or potential risks,” Tchang adds.
Should You Stop Taking Weight Loss Medications if You Are on Birth Control?
In short, no, you should not stop taking tirzepatide if you are concerned about getting pregnant, says McBane.
“Someone who is taking or thinking about taking tirzepatide should consider switching to a contraceptive other than the pill,” she says, adding that there are many options for birth control, so the fact that tirzepatide may make oral methods less effective shouldn’t deter people from taking the medication. “The specific method will really depend on that individual’s preferences and reason for using the contraceptive.”
Although birth control patches, rings, injections, implants, and intrauterine devices (IUDs) do not carry any risk of being dampened by tirzepatide or semaglutide. “It is always a good idea to use a backup form of birth control, but especially since we do not have data on how these medications can affect pregnancy,” Tchang says.
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