This sheet is about exposure to phentermine in pregnancy and while breastfeeding. This information is based on available published literature. It should not take the place of medical care and advice from your healthcare provider.
What is phentermine?
Phentermine is a medication that has been used as an appetite suppressant to treat obesity. Some brand names for phentermine are Adipex®, Fastin®, Ionamin®, Lomaira™®, or Zantryl®. The combination of phentermine and topiramate is sold under the brand name Qsymia®. MotherToBaby has a fact sheet on topiramate here: https://mothertobaby.org/fact-sheets/topiramate/.
Sometimes when people find out they are pregnant, they think about changing how they take their medication, or stopping their medication altogether. However, it is important to talk with your healthcare providers before making any changes to how you take this medication. Your healthcare providers can talk with you about the benefits of treating your condition and the risks of untreated illness during pregnancy.
The product labels for phentermine and the combination of phentermine and topiramate recommend people who are pregnant not use these medications. The benefit of using phentermine in a pregnancy may outweigh possible risks. Your healthcare providers can talk with you about using phentermine and what treatment is best for you.
Obesity can make it harder to get pregnant, and increase the chance of miscarriage, birth defects, or other pregnancy complications. MotherToBaby has a fact sheet on obesity here: https://mothertobaby.org/fact-sheets/obesity-pregnancy/.
I am taking phentermine, but I would like to stop taking it before getting pregnant. How long does the drug stay in my body?
The time it takes the body to metabolize (to process) medication is not the same for everyone. In healthy non-pregnant adults, it takes up to 8 days, on average, for most of the phentermine to be gone from the body.
I take phentermine. Can it make it harder for me to get pregnant?
Studies have not been done to see if taking phentermine could make it harder to get pregnant.
Does taking phentermine increase the chance of miscarriage?
Miscarriage is common and can occur in any pregnancy for many different reasons. Studies have not been done to see if phentermine can increase the chance of miscarriage.
Does taking phentermine increase the chance of birth defects?
Birth defects can happen in any pregnancy for different reasons. Out of all babies born each year, about 3 out of 100 (3%) will have a birth defect. We look at published data to try to understand if an exposure, like phentermine, might increase the chance of birth defects in a pregnancy. There is little information on phentermine exposures during early pregnancy. The available data does not suggest an increased chance of birth defects.
Does taking phentermine in pregnancy increase the chance of other pregnancy-related problems?
Studies have not been done to see if phentermine increases the chance for pregnancy-related problems such as preterm delivery (birth before week 37) or low birth weight (weighing less than 5 pounds, 8 ounces [2500 grams] at birth).
Does taking phentermine in pregnancy affect future behavior or learning for the child?
Studies have not been done to see if phentermine can increase the chance of behavior or learning issues for the child.
Breastfeeding while taking phentermine:
Studies have not been done on the use of phentermine while breastfeeding. The product labels for phentermine and the combination of phentermine and topiramate recommend people who are breastfeeding not use these medications. The benefit of using phentermine may outweigh possible risks. Your healthcare providers can talk with you about using phentermine and what treatment is best for you. Be sure to talk to your healthcare provider about all your breastfeeding questions.
If a male takes phentermine, could it affect fertility or increase the chance of birth defects?
Studies have not been done to see if phentermine could affect male fertility (ability to get partner pregnant) or increase the chance of birth defects. In general, exposures that fathers or sperm donors have are unlikely to increase the risks to a pregnancy. For more information, please see the MotherToBaby fact sheet Paternal Exposures at https://mothertobaby.org/fact-sheets/paternal-exposures-pregnancy/.
Please click here to view references.
OTIS/MotherToBaby encourages inclusive and person-centered language. While our name still contains a reference to mothers, we are updating our resources with more inclusive terms. Use of the term mother or maternal refers to a person who is pregnant. Use of the term father or paternal refers to a person who contributes sperm.
