Phentermine and Pregnancy
Since phentermine is chemically related to amphetamines, which have been shown to cause miscarriages and birth defects, it may not be safe for pregnant women. In fact, since weight loss is generally not recommended during pregnancy, the FDA has classified phentermine as a pregnancy Category X drug. If you are taking this medicine and pregnancy occurs, be sure to let your healthcare provider know.
Phentermine is a prescription weight-loss aid. Since phentermine has not been studied in any pregnant animals or women, it is not known if it is safe for use during pregnancy.
The U.S. Food and Drug Administration (FDA) uses a category system to classify the possible risks to a fetus when a specific medicine is taken during pregnancy. Pregnancy Category X is given to medicines that show problems to the fetus in animal studies or in human use of the medication. With this category, the potential risks clearly outweigh the potential benefits.
Phentermine has not been adequately studied in pregnant women or pregnant animals. Therefore, the effects of the medicine on a developing baby are not completely known. A similar medication increased the risk for lung problems and miscarriage when given to pregnant rats.
There have been reports of miscarriage or stillbirth occurring in women who took phentermine in early and late pregnancy. There have also been reports of heart valve problems in a newborn born to a woman who took phentermine early in pregnancy. It is difficult to say for certain whether the medication or something else caused these problems.
Perhaps more importantly, a pregnant woman is unlikely to benefit from the use of phentermine. This is because pregnant women are generally advised to not lose weight while pregnant, even if they are already overweight when becoming pregnant. Because phentermine would not be absolutely necessary for a pregnant woman, it is recommended that the medication be avoided during pregnancy.