pregnancy and phentermine

I Took Phentermine and Didn’t Know I Was Pregnant. Does Taking Phentermine Affect Pregnancy?

, reviewed by
 – Updated May 8, 2023
, reviewed by
 – Updated May 8, 2023
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Table of Contents

Is taking Phentermine while pregnant allowed?

Doctors advise against trying to lose weight during pregnancy.

The future child benefits from its mother gaining weight instead of losing it.

This is a fact despite the potential complications associated with obesity.

The additional risks associated with Phentermine and pregnancy are the negative effects over the unborn child’s health.

However, the effects of Phentermine on pregnant women and on the developing fetus have not been sufficiently studied yet.

We can cite only one study, which was conducted by the FDA. The study paper describes the case of a woman who took Phentermine during the first two trimesters of pregnancy. As a result, she gave birth to a baby with bilateral porencephalic cysts. The researchers speculate that this may have been due to an intrauterine stroke.

The FDA classifies Phentermine as a category C drug for pregnant women. It is assigned to a category of drugs that have not been studied in humans or animals but could theoretically harm the fetus.

Accidentally took Phentermine while pregnant

If you accidentally took Phentermine while pregnant, avoid doing it again and report it to your doctor.

You may find out that you got pregnant while taking Phentermine. You will have to decide whether to continue the treatment during the first trimester of pregnancy or stop it. Discuss this with your doctor because there is no accurate information about the drug’s negative effects.

There is a 2012 study published in Neuroendocrinology Letters. It compares birth outcomes in women who took appetite suppressants during pregnancy, such as Phentermine, with those who did not. The study reported that no notable differences were found.

Another study, conducted by Teratology in March 2002, noted a higher risk of gestational diabetes in people who took a combination of Phentermine and Fenfluramine during the first trimester of pregnancy compared to those who did not.

Can you take Phentermine while trying to get pregnant

Since there is no comprehensive data on whether Phentermine is safe to take during pregnancy, it is not recommended for both pregnant women and those trying to get pregnant.

How long should I be off Phentermine before getting pregnant

The average half-life of Phentermine is approximately 20 hours. This period decreases to 7-8 hours if a person has consumed food with a Ph-factor lower than 7.

Two days is enough for Phentermine to be completely eliminated from the body.

In other words, even if you took the last dose two days before conception, the pregnancy should not be affected in any way.

Can Phentermine cause a positive pregnancy test

This is highly unlikely. Pregnancy tests are designed specifically to determine the presence of HCG (Human Chorionic Gonadotropin). This hormone is usually not present in diet pills, and this includes Phentermine.

Can Phentermine cause miscarriage

There is no evidence to support the possibility of miscarriage when using Phentermine. In one study done on the effects of Fen-Phen (Phentermine/Fenfluramine) in the first trimester of pregnancy, researchers concluded that the risk of miscarriage was not increased.

Does Phentermine make you more fertile

The answer is yes. However, it has nothing to do with the drug itself. Simply getting rid of excess weight, both in men and women, almost automatically leads to an increase in fertility. Improved hormonal balance is one example of this.

The opposite effect is possible too. This study has shown that the chance of spontaneous conception decreases as body weight increases.


There are no sufficient studies on the effect of Phentermine on pregnancy. However, doctors do not recommend taking any weight-loss drugs during pregnancy. Phentermine is no exception.

Therefore, if you accidentally took Phentermine during pregnancy, do not do it again and tell your doctor about it.

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