Phentermine And Pregnancy: Safety Profile And Possible Side Effects

✔ Research-backed

It is typical for women to gain weight during pregnancy. However, some pregnant women may become aware of these changes in their bodies and attempt to lose weight with prescription drugs, such as phentermine. But is it safe to take phentermine during pregnancy? Does it affect the fetus?

This post tells you if phentermine is safe to use during pregnancy and its potential effects.

In This Article

What Is Phentermine?

Phentermine (Supreza) is a short-term medication prescribed to help lose weight in overweight women. It is recommended with an exercise regimen and diet modification to those experiencing obesity or who have a body mass index (BMI) greater or equal to 30kg/m2 (1). It is available under the brand names Adipex, Fastin, Ionamin, Zantryl.

This drug belongs to the class “anorectics,” which helps in weight reduction by suppressing the appetite, although actions on the central nervous system and metabolism may also be involved.

Is It Safe To Take Phentermine During Pregnancy?

Phentermine adversely affects you and your baby during pregnancy.

Image: Shutterstock

No. The US Food and Drug Administration classified phentermine (Supreza) as “Pregnancy Category X” drug (1), which means that studies in animals or humans have proved to have adverse effects on the developing fetus, and the risks of taking this medicine outweigh the potential benefits.

Phentermine is not recommended because weight loss has no potential benefit during pregnancy, and this medication might also harm the fetus or cause certain pregnancy complications.

Does Taking Phentermine During Pregnancy Cause Any Birth Defects?

Very few human studies were conducted on phentermine’s pharmacokinetics to determine if its teratogenicity is responsible for any birth defects or adverse effects, such as fetal growth restriction, during fetal development in pregnant women.

A study on pregnant women in the Czech Republic, which focused on the effects of appetite suppressants like sibutramine and phentermine, found that there were no differences in pregnancy outcomes between the women who took the drugs and those who did not (2).

Another controlled cohort study, where 98 pregnant women who took medication were compared to 233 women who did not, found that (3)

  • There were no significant differences between the groups in spontaneous pregnancy loss or premature delivery.
  • The exposed group showed a significant increase in neonatal outcomes such as birth weight and head circumference of the newborn.
  • The rate of gestational diabetes was high in women who took phentermine.

    Phentermine may increase the risk of gestational diabetes.

    Image: Shutterstock

A drug review on Qsymia (pregnancy category X drug) – a weight management drug that is a combination of phentermine and topiramate – says that topiramate is said to interfere with embryonic development and cause cleft palate in babies, indicating its possible associations with the risk of congenital malformations (4).

Side Effects Of Phentermine

Phentermine may cause drowsiness.

Image: Shutterstock

Along with the birth defects, phentermine may also have the following side effects on maternal health (5).

  • Mood swings
  • Altered thought processes
  • Suicidal ideas and behaviors
  • Dizziness
  • Drowsiness
  • Impaired cognition
  • Dry mouth
  • Unusual thirst
  • Diarrhea
  • Constipation
  • Painful menstrual periods
  • Heartburn
  • Hair loss
  • Suppresses appetite

A mother shares her experience of discovering her pregnancy while taking phentermine and the symptoms she encountered during that time. She explains, “The symptoms I was having, I wasn’t able to figure out if it was the medicine (phentermine) or if it was due to pregnancy or getting my period. I was also drinking a lot of water because those pills make you thirsty. I would have headaches, and I was dizzy, but I didn’t know if it was because I was not eating all the calories that I was used to eating because, like I said, the medicine reduces hunger (i).” She finally stopped taking the medicine after she knew she was pregnant.

protip_icon Be watchful
Sympathomimetic appetite suppressants such as phentermine may lead to mitral valve disease, stroke, or pulmonary hypertension (9).

Does Phentermine Cause Withdrawal Symptoms?

A clinical intervention trial, including patients on long-term phentermine use, stated that “phentermine treatment does not induce drug cravings. Also, amphetamine-like withdrawal does not occur upon abrupt treatment cessation at higher doses (6).”

Evidence-based medicine analysis shows that taking more than the advised phentermine dosage may result in unfavorable side effects. For example, there were reports that people taking more than the prescribed dosage experienced extreme fatigue, mental depression, and changes in sleep patterns (1).

Taking more than the prescribed dosage may cause mental depression.

Image: Shutterstock

So, if you are on phentermine and found out that you are pregnant, then consult your doctor and take advice on how to stop using this drug.

How Soon Can You Take Phentermine After Having A Baby?

There aren’t enough studies to determine if phentermine passes into breast milk when breastfeeding, so you need to consult your doctor or maternal-fetal medicine specialist to determine when it is safe to take phentermine after having a baby.

protip_icon Point to consider
The label of the medicine states that nursing mothers should not consume this medicine (7).

Frequently Asked Questions

1. Can I take phentermine if I am trying to get pregnant?

There is not much information on how it may impact women planning to conceive (7). In any case, taking the medication without consulting the doctor is not advisable.

2. What happens if you stop taking phentermine suddenly?

Studies have shown no reported adverse effects of stopping phentermine, including no withdrawal symptoms (8). Nevertheless, if you have been taking this medication before pregnancy, consult a doctor before discontinuing once you have confirmed your pregnancy.

3. Are there alternative weight management options for pregnant women besides phentermine?

Gaining weight during pregnancy is normal; incorporating a few food habits and lifestyle changes can help manage weight. These changes include consuming more fruits, vegetables, whole grains, lean proteins, and low-fat dairy products. Avoid desserts, soft drinks, fried foods, and fatty meats. Include 150 minutes of workout or physical activity weekly. You can work this regimen with your doctor or a nutritionist to ensure you meet your caloric needs throughout pregnancy (10).

4. Can Phentermine increase the risk of miscarriage?

Miscarriage can occur in any pregnancy for various reasons. Not enough studies prove that Phentermine can cause miscarriages (11).

Maternal weight gain during pregnancy is normal, but many women are concerned about it and take weight-loss medication, such as phentermine, to manage it. However, taking phentermine while pregnant is not safe as it may adversely affect the fetus. Although clinical trials show that phentermine does not create withdrawal symptoms, you may experience fatigue and depression if the medication is taken in a high dosage. Women may also experience other side effects such as mood swings, dizziness, and dry mouth. So, the best thing to do is take care of your diet and exercise regularly to stay healthy and happy. If you want to take any medications during pregnancy, talk to your doctor to ensure proper medical safety.

Infographic: Possible Side Effects Of Phentermine During Pregnancy

Phentermine is a drug known to cause appetite suppression and is usually prescribed for weight loss. However, it is not recommended as safe for pregnant women due to concerns over its potential risk of adverse effects during pregnancy. In the infographic below, let us have a look at the possible side effects of phentermine in pregnant women.

common adverse effects of phentermine in pregnancy (infographic)

Illustration: Momjunction Design Team

This post is for informational purposes only and is not a replacement for a doctor’s consultation. Do not use any medication without talking to your doctor.

Key Pointers

  • Phentermine (Supreza) is a weight loss drug used in overweight women.
  • The FDA has categorized it as a “Pregnancy Category X” due to potential harm to the fetus.
  • Mood swings, impaired cognition, diarrhea, hair loss, drowsiness, and dry mouth are some of the medication’s side effects.
  • Some studies have shown a link between phentermine use and gestational diabetes and congenital disabilities.
  • Taking more than the prescribed dose can result in extreme fatigue, changes in sleep patterns, and depression.
phentermine while pregnant_illustration

Image: Dalle E/MomJunction Design Team

Personal Experience: Source


MomJunction's articles are written after analyzing the research works of expert authors and institutions. Our references consist of resources established by authorities in their respective fields. You can learn more about the authenticity of the information we present in our editorial policy.

1. Prescribing Information- Suprenza; The US Food and Drug Administration
2. Manakova E, Kralova T, Hubičková Heringová L; Appetite Suppressants During Pregnancy; NCBI (2012)
3. Jones KL, Johnson KA, Dick LM, Felix RJ, Kao KK, Chambers CD; Pregnancy outcomes after first trimester exposure to phentermine/fenfluramine; NCBI (2002)
4. John D. Gazewood; Kathleen Barry; Phentermine/Topiramate (Qsymia) for Chronic Weight Management; The American Association Of Family Physicians
5. Phentermine and Topiramate; Medline Plus; US National Library of Medicine
6. Hendricks EJ; Addiction potential of phentermine prescribed during long-term treatment of obesity; NCBI (2014)
7. Phentermine; Mother to baby
8. Ed J Hendricks and Frank L Greenway; A study of abrupt phentermine cessation in patients in a weight management program; NCBI
9. Nathan D’Adesky and Suman Ghosh; Phentermine Use During First and Second Trimesters Associated with Fetal Stroke; NCBI (2019)
10. Weight gain during pregnancy; CDC
11. Phentermine; Mother to Baby

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Dr. Shashwat Jani is a consultant obstetrician & gynecologist in Smt. N.H.L. Municipal Medical College, Ahmedabad. He has 14 years of experience with a special interest in high-risk pregnancy, infertility, and endoscopy. He has written 12 chapters in reference books of Ob/Gyn and published 18 articles in Index journals. Dr. Jani has been invited as faculty in more than full bio