Is It Safe to Take Phentermine During Pregnancy?

by Marixie Ann Obsioma, MT, undergrad MD on January 9, 2019
Last updated on May 23, 2021

If you started off your pregnancy carrying extra weight for your height, you are definitely not alone!

photo of a pregnant woman

More than half of pregnant women are either overweight or obese (1).

The increasing number of maternal obesity cases has become a major problem in the field of obstetrics and gynecology.

Maternal obesity can cause negative outcomes for both moms and babies (2).

Maternal risks would include gestational diabetes and pre-eclampsia. Babies are at risk for stillbirth and congenital problems (2).

While pregnancy is certainly not the time to go on a weight loss diet, a lot of plus-size pregnant women still want to use drugs like Phentermine.

As will be discussed in details below, Phentermine will have effects on moms and babies.

Luckily, you can still keep a healthy pregnancy weight naturally.

What is Phentermine?

Phentermine is a well-known prescription drug that can help suppress appetite.

It is classified as a sympathomimetic amine (3).

When used as an adjunct to low-calorie diet and exercise, it can be effective for the purpose of weight loss.

This drug, however, is only advisable for short-term use (3).

How should one take Phentermine?

Follow all directions printed on the label. Never take this drug in larger amounts or for longer than prescribed.

Phentermine is best taken on an empty stomach, except for disintegrating tablets, which can be taken before or after a meal (4).

To avoid sleep problems, take this drug early in the morning (4).

As mentioned earlier, this must be taken only for a short period of time.

Taking more of this drug will not make it more effective and may cause detrimental side effects (4).

Keep at room temperature free from heat and moisture.

Do not stop using Phentermine abruptly to avoid withdrawal symptoms (4). Know to stop using this drug safely by consulting a medical doctor.

Can You Use Phentermine During Pregnancy?

Generally, it is not advisable to use Phentermine during pregnancy as it can cause danger to fetal health (5).

First and foremost, weight loss is not ideal during pregnancy. Your baby needs proper nutrition to grow healthy.

Also, the US Food and Drug Administration (FDA) has classified Phentermine under category X drugs. This group of drugs may harm the fetus. The risks also outweigh the drug’s benefits for pregnant women (6).

Phentermine can cause fetal birth defects like cleft lip and cleft palate, which may occur early in the pregnancy (7).

Possible Effects of Phentermine on Pregnant Women

Little is known about Phentermine use and its possible effect on pregnant women.

One study revealed a higher risk of gestational diabetes among pregnant women who took Phentermine during the first trimester (8).

However, this increased risk can likewise be related to being overweight, to begin with. This factor was not ruled out in the study.

Gestational diabetes can be dangerous (9). It can cause several complications like:

  • Delivery complications because of a huge baby
  • High blood pressure
  • Adult-onset diabetes after pregnancy
  • Pre-eclampsia

Pre-eclampsia normally happens after the 20th week. There is an increase in blood pressure, which can be life-threatening to both the mom and baby. This may also cause kidney failure (3).

Once diagnosed with pre-eclampsia, the baby must be delivered immediately.

Studies on Risks to Babies

As mentioned above. Phentermine is known to cause fetal birth defects, but some studies that exist do not seem to confirm this information.

A small study was conducted in the Czech Republic comparing pregnant women who took Phentermine and those who did not. There’s no difference in pregnancy outcomes (10).

Another study looked at the use of Phentermine and Fenfluramine in the first trimester of pregnancy. The result showed no increased risks of pregnancy loss and birth defects (11).

While the above-mentioned studies do not connect Phentermine with serious side effects, Phentermine is still related to weight loss.

Weight loss during pregnancy can put your baby at risk of the following complications:

  • Small for gestational age. This increases a baby’s risk of trouble maintaining body temperature, difficulty breathing, and low blood sugar (9).
  • Death in the first year of life. According to one study, babies born to women without a healthy weight during pregnancy had three times the risk of dying in their first year of life (12).
  • Disabilities. Pregnant women who excessively limit their calorie intake will prompt the body to use fat stores for energy. The process of breaking down fats will produce ketones. This puts babies at risk of mental deficiencies (9).
  • Neural tube defects. One study suggests that the use of weight loss products while pregnant can raise the risk of babies of defects affecting the brain and spine (13).

Now you know that weight loss drugs like Phentermine are not the best answer to keep a healthy weight during pregnancy.

Don’t fret as you can take several measures to maintain your body in good shape during pregnancy.

Best Ways to Lose Weight While Pregnant

1. Minimize Calorie Intake

The most ideal way to reduce weight safely during pregnancy is to minimize calorie intake without overdoing it.

Moms must consult a dietitian to make ideal meal plans. You have to be sure that you are not cutting the supply of nutritious foods while trying to limit your calorie intake.

Doctors recommend that pregnant women should not go below 1,700 calories per day (14).

This is the minimum calorie count needed to ensure that you and your baby will get an adequate amount of nutrients and energy regularly.

2. Take Prenatal Vitamins

Prenatal vitamins can help ensure that your body is getting all of the nutrients needed for you and your baby.

Folate is very important. It can help reduce the risk of birth defects (14).

3. Exercise Daily

Most women think that exercises can harm their babies. But, this is not true, especially when done in moderation and in the right trimester.

Exercising can help maintain a mom’s body weight, minimizing birth defects and reducing pains and aches that she may experience during pregnancy (14).

Doctors recommended 30 minutes of activity per day (14). If you feel like this is too much to start, you can break it into shorter sessions throughout the day.

Some of the recommended weight loss exercises for pregnant women include yoga, walking, jogging, and swimming (14).

4. Eat Ginger

Ginger, a favorite in Southeast Asia is commonly used in food and medicine. Its plant is rich in natural chemicals that are good for health and wellness.

Ginger is available in different forms – candies, teas, ales, or water.

It offers several health benefits because of its anti-inflammatory, antioxidant, and anti-nausea effects. Ginger can also promote weight loss if combined with diet and exercise.

One study showed that ginger had an anti-obesity action in rats on high-fat diets (16). Another research found that men who took a hot ginger drink after a meal felt more full longer (17).

5. Get Extra Sleep

Catching up on rest and sleep and reducing stress can work wonders for your cravings.

Poor sleep has long been connected to weight gain and a higher body mass index (BMI) (18).

One review found that lack of sleep can increase the likelihood of obesity by 55% in adults and 89% in kids (19).

Another study included 60,000 non-obese nurses for more than a decade. Results showed that those who slept fewer hours daily were 15% more likely to be obese (20).

6. Stay Hydrated

Water can suppress one’s appetite.

It makes your stomach feel full, thus sending signals to the brain to stop eating.

One study followed 50 overweight women for 8 weeks. They were asked to drink 500mL of water 30 minutes before every meal, in addition to their usual water intake.

They experienced a decrease in body weight, BMI, and body fat. There’s also less appetite (21).

Drink at least 2-3 liters of water daily. You have to stay hydrated during pregnancy (15).


The fact is losing or gaining weight could be part of a healthy pregnancy. Some may lose weight during the first trimester and add pounds in the succeeding months.

As discussed earlier, you can stand to lose extra pounds without harming yourself and your baby.

The key is to stay aware of your body needs and do things naturally!


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