Phentermine Pregnancy and Breastfeeding Warnings

Brand names: Adipex-P, Atti-Plex P, Fastin, Ionamin, Lomaira, Obenix, Obephen, Oby-Cap, Oby-Trim, Panshape M, Phentercot, Phentride, Pro-Fast HS, Pro-Fast SA, Pro-Fast SR, Suprenza, T-Diet, Teramine, Teramine ER, Zantryl

Medically reviewed by Drugs.com. Last updated on Jul 17, 2025.

Phentermine Pregnancy Warnings

Use is not recommended during pregnancy; some experts state that use of this drug is contraindicated.

AU TGA pregnancy category: B2
US FDA pregnancy categories:
-Oral, 8 mg tablets: Not assigned.
-Oral, 37.5 mg tablets: X

Risk summary: Maternal weight loss may result in fetal harm.

Comments:
-Weight loss offers no potential benefit to a pregnant woman; a minimum weight gain, and no weight loss, is currently recommended for all pregnant women, including those who are already overweight or obese, due to obligatory weight gain that occurs in maternal tissues during pregnancy.
-If a female patient becomes pregnant during therapy, she should be apprised of the potential harm to a fetus.

Animal studies conducted during late gestation administered at doses 7 times the maximum human dose (MHD) have failed to reveal evidence of fetal and maternal harm. There are no information on teratogenicity. There are no controlled data in human pregnancy.

AU TGA pregnancy category B2: Drugs which have been taken by only a limited number of pregnant women and women of childbearing age, without an increase in the frequency of malformation or other direct or indirect harmful effects on the human fetus having been observed. Studies in animals are inadequate or may be lacking, but available data show no evidence of an increased occurrence of fetal damage.

US FDA pregnancy category X: Studies in animals or humans have demonstrated fetal abnormalities and/or there is positive evidence of human fetal risk based on adverse reaction data from investigational or marketing experience, and the risks involved in use of the drug in pregnant women clearly outweigh potential benefits.

US FDA pregnancy category Not Assigned: The US FDA has amended the pregnancy labeling rule for prescription drug products to require labeling that includes a summary of risk, a discussion of the data supporting that summary, and relevant information to help health care providers make prescribing decisions and counsel women about the use of drugs during pregnancy. Pregnancy categories A, B, C, D, and X are being phased out.

See references

Phentermine Breastfeeding Warnings

Use should be avoided during breastfeeding

Excreted into human milk: Unknown
Excreted into animal milk: Data not available

Comments: Because of the potential for serious adverse reactions in nursing infants, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.

See references

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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