Phentermine during pregnancy

When being pregnant, woman should always be cautious about any medications. Pregnant woman should not take nutritional supplements, vitamins and diet pills (in particular Phentermine) without consulting a doctor.

Phentermine weight loss drug is contraindicated in pregnancy. In pregnancy, woman should gain weight, not lose it.

  • Losing weight during pregnancy may bring obese women more harm, than good. Also, losing weight in pregnancy can negatively affect fetal development.

Phentermine is a prescription drug, which is used to treat obesity. 

The FDA has developed a classification system for drugs, according to their potential teratogenicity. However, categorizing drug to one group or another is not always supported by epidemiological studies. In most cases, pregnant women are excluded from all clinical trials.

Nevertheless, the FDA determined Phentermine to category X. This means that pregnant women do not participate in Phentermine clinical trials. There are several reports on possible development of pulmonary disease in babies and stillbirth, when Phentermine was taken during pregnancy in animals.

Phentermine is chemically similar to amphetamines. Studies have shown that drugs of amphetamine group increase the risk of miscarriage and birth defects in fetal development.

There is no accurate data on Phentermine safety in pregnancy. Therefore, Phentermine is contraindicated in women during pregnancy. Women, who want to conceive, are also contraindicated to take Phentermine for losing weight.


Post clinical observations have shown that weight loss during pregnancy increases risk to fetus. So, before prescribing Phentermine, the doctor should ask woman about a possible pregnancy. Woman should start anti-obesity therapy, only if the pregnancy test is negative.

Moreover, women of childbearing age are recommended to use means to prevent pregnancy, when going through pharmacotherapy with Phentermine. If a woman doesn’t plan to get pregnant soon, she can use Implanon. It is a new method of birth control.

Implanon is a hormone-releasing birth control implant, which helps prevent pregnancy for up to 3 years.

  • The implant is a flexible plastic rod of a matchstick size. Implanon has progestin hormone etonogestrel and doesn’t contain estrogen.

It is known that estrogen-containing birth control pills promote weight gain. When taking Phentermine, Implanon is the best means of birth control, because this prescription drug for preventing pregnancy does not contain estrogen hormone.

If a woman still detects pregnancy, a few weeks after starting anti-obesity therapy, she should immediately stop taking Phentermine pills and inform her doctor.

Women, who took Phentermine in early pregnancy, should overdo tests, which will help to determine possible physical birth defects in the fetus.

Phentermine is also contraindicated in breastfeeding. 

There is no accurate data on Phentermine penetration into breast milk. However, there are reports that other amphetamine-containing drugs penetrate into breast milk. Given that Phentermine suppresses appetite, it may negatively affect development of a baby.

  • Phentermine affects the central nervous system, and can increase blood pressure, which causes sleeplessness, dizziness, nervousness. Therefore, these side effects are likely to manifest in the baby, when Phentermine penetrates into a baby’s body with mother’s milk.

Considering possible severe side effects, it is recommended to determine the value of weight loss drug to the mother, before taking Phentermine. If weight loss is advantageous for the mother, she should stop breastfeeding and begin anti-obesity therapy with Phentermine.