Phentermine And Pregnancy: Safety Profile And Possible Side Effects

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Women put on weight during pregnancy, and that is normal. However, some women may become conscious of their new curves and try to reduce weight using medications like phentermine. Is it safe to use this drug during pregnancy? Read on as MomJunction tells you about using phentermine during pregnancy.

What Is Phentermine?

Phentermine (Supreza) is a short-term medication prescribed to help lose weight in overweight women. It is recommended in adjunction with an exercise regimen, and diet modification, to those with 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?

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 during pregnancy because the weight loss has no potential benefit during pregnancy, and this medication might also harm the fetus.

Does Taking Phentermine During Pregnancy Cause Any Birth Defects?

Very few human studies were conducted to determine whether phentermine is responsible for any birth defects when used during pregnancy.

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.
  • Birth weight and head circumference of the newborn were significantly increased in the exposed group.
  • The rate of gestational diabetes was high in women who took phentermine.

A drug review on Qsymia (pregnancy category X drug) – a weight management drug which is a combination of phentermine and topiramate – says that topiramate is said to cause cleft palate in babies (4).

Side Effects Of Phentermine

Along with the birth defects, phentermine may also have the following side effects (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

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).”

However, there were reports that people who took more than the prescribed dosage experienced extreme fatigue and mental depression, and changes in sleep patterns (1).

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 the breast milk, so you need to consult your doctor to determine when it is safe to take phentermine after having a baby.

Gaining weight during pregnancy is normal. So do not panic if you’ve gained a few extra pounds. Follow a nutritious diet and exercise regularly to have a healthy and happy pregnancy. If you still want to take any medication for losing weight during pregnancy, talk to your doctor to avoid any adverse outcomes.

How did you manage your weight during pregnancy? Let us know in the comments section below.

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.


MomJunction's health articles are written after analyzing various scientific reports and assertions from expert authors and institutions. Our references (citations) 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)

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