This sheet talks about exposure to phentermine in a pregnancy and while breastfeeding. This information 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®. It is also an ingredient in Qsymia®.
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.
Is phentermine the same as Fen-Phen?
No. Fen-Phen was a medication made of fenfluramine and phentermine prescribed to help people lose weight. Fenfluramine was taken off of the market in September 1997 because of the concern that it caused heart problems. Phentermine is still available.
Can losing weight impact my pregnancy?
It is not recommended that you lose weight during pregnancy. Some studies suggest that dieting during early pregnancy may increase the chance of having a baby with a neural tube defect (when the baby’s spine does not form properly). Spina bifida is an example of a neural tube defect. However, being significantly overweight increases the chance of some medical complications in pregnancy. These include gestational diabetes (diabetes that develops and lasts only during pregnancy) and high blood pressure. Your healthcare provider can discuss recommendations about weight gain or loss during pregnancy.
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 for a woman to get pregnant.
Does taking phentermine increase the chance for miscarriage?
Miscarriage is common and can occur in any pregnancy for many different reasons. Studies have not been done to see if phentermine increases the chance for miscarriage.
Does taking phentermine increase the chance of birth defects?
Every pregnancy starts out with a 3-5% chance of having a birth defect. This is called the background risk. . There is little information on phentermine exposures during early pregnancy. The available data does not suggest an increased chance for 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 cause behavior or learning issues for the child.
Breastfeeding while taking phentermine:
Studies have not been done on phentermine while breastfeeding. The product label for phentermine recommends people who are breastfeeding not use this medication. Be sure to talk to your healthcare provider about all of your breastfeeding questions.
If a male takes phentermine, could it affect fertility (ability to get partner pregnant) or increase the chance of birth defects?
Studies have not been done to see if phentermine could affect male fertility 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/.
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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.