phentermine and pregnancy

Phentermine and pregnancy: Can they go hand in hand?

September 23. 2022

Pregnancy weight gain is a normal part of a healthy, growing body. However, when those pregnancy cravings kick in, and the added pounds get a little out of hand, many women start looking for ways to suppress their appetite and prevent further weight gain. One of the first solutions they run into is typically phentermine – an FDA-approved appetite suppressant used to treat obesity in patients with a high BMI score and overly increased hunger. While phentermine does have a high success rate when used correctly and under an experienced physician’s supervision, the question arises: can phentermine and pregnancy go hand in hand?

In today’s article, our weight loss clinic in Chicago breaks down the topic to ensure you gain a better understanding of the use of phentermine during pregnancy.

What is phentermine?

Phentermine belongs to a group of drugs known as anorectics; its primary role is to suppress appetite while boosting the fat loss process and the overall metabolism function. This drug was approved for medical use back in 1959, and numerous research conducted since then have shown that phentermine should not be combined with other weight loss drugs to minimize its side effects. Short-term use of phentermine is now a part of many medically-supervised weight loss programs and can only be taken with a prescription. It works by stimulating certain parts of your brain to reduce hunger and increase energy. As with any other drug, phentermine may come with a few common side effects, including:

  • dry mouth
  • headache
  • dizziness
  • abdominal stomach pain

Although this drug holds a high weight loss success rate when used correctly, not everyone is eligible to start taking phentermine; the drug is mainly used to treat obese patients with overly increased hunger and a BMI equal to or higher than 27. It is paired with an adequate diet and physical activity to treat obesity in people at a higher risk of developing diabetes, high blood pressure, or high cholesterol. With that in mind, it’s essential to consult an experienced physician who will complete a thorough medical examination before deciding whether phentermine is the right fit for you.

Phentermine and pregnancy: Should you take it?

Now that we’ve covered the essentials let’s dive in to see whether pregnant women are eligible to start taking phentermine.

When it comes to fertility, the use of phentermine won’t significantly reduce the likelihood of conceiving. In case you took phentermine as prescribed before you found out that you’re expecting, there’s no need to worry since all its traces are likely flushed out from your system in a few days after your last dose and, therefore, shouldn’t affect the development of the fetus. However, if you’re planning to have a baby and trying to conceive, we advise you not to start taking this drug or discontinue its use if you’ve been taking it already. The main reason behind this is that the link between phentermine and pregnancy is not yet developed, determined, or proven. Still, according to the FDA, phentermine belongs to a pregnancy category X, meaning they’ve been studied in either pregnant women or pregnant animal subjects and resulted in fetal abnormalities. With that in mind, it is improbable for any doctor to prescribe phentermine or appetite suppressants in general to a pregnant woman.

Phentermine before pregnancy: Are there risks?

Sometimes, women may continue to use phentermine as prescribed during their first trimester, typically because they still don’t know that they’re expecting. In such cases, it’s best to inform your doctor about the use of phentermine as soon as you confirm your pregnancy and discontinue the use to allow your body and the fetus to grow properly. A small study from 2012 has shown that there was no significant difference in pregnancy outcomes between people who took appetite suppressants during pregnancy and those who didn’t. With that in mind, there’s no need to stress or worry because the unintentional use of phentermine in the first trimester of pregnancy shouldn’t harm your ability to carry a healthy baby to term. If you have any uncertainties regarding the use of phentermine before pregnancy, don’t hesitate to schedule a call with medical professionals who will answer your questions.

Phentermine and breastfeeding

It’s not uncommon for women to start thinking about taking phentermine after pregnancy. Although phentermine itself has not been studied to determine its effect on breastfeeding, studies with similar drugs have shown that such substances typically find their way into breast milk. Side effects that may occur in such instances include a baby’s difficulty sleeping and a decreased interest in regular feeding. With that in mind, it’s not advisable for mothers to start taking phentermine after pregnancy until they stop breastfeeding.

It’s essential to remember that while you’re breastfeeding, your body goes through numerous processes to get itself back into its regular state. One of the outcomes of such processes is often natural weight loss – even though you may consume more food to sustain breastfeeding, your body is actually burning calories to produce enough milk, eventually causing you to lose weight. Therefore, it’s best to focus your diet on highly nutritious foods and make some time for any type of physical activity to boost natural weight loss if your pregnancy allows you so.

Why does the appetite often increase during pregnancy?

As mentioned earlier, a pregnant body is meant to grow; your body demands more nourishment to support a developing baby. The increase in hunger may happen during any point of your pregnancy, but it typically occurs during the second trimester, once the morning sickness and nausea end. Your body genuinely needs more calories, typically an additional 300-350kcal per day in your second trimester and up to an additional 500kcal in the third one. There’s usually no need to significantly increase your calorie intake during the first trimester. Considering all of the above, your doctor will keep track of your weight to ensure that it’s under control and growing at an expected pace. Sudden or excessive weight gain may require a few measures to avoid certain weight-related risks, but overall your goal should be set on providing your body with all the essential nutrients instead of losing weight. It’s also important to note that if your body doesn’t absorb nutrients well enough, your hunger levels may increase because of it.

Five best ways to keep your body weight under control during pregnancy

It’s well-known that gaining too much weight during pregnancy can negatively impact both the mother and the developing baby. Therefore, it’s advisable to take some steps to prevent such an outcome and maintain a healthy weight and a nourished body. The following tips may help you in achieving these goals:

Improve your diet

If you’re unsure about the number of nutrients your body needs during pregnancy, ask your doctor to recommend a diet that will fulfill your needs. Loading up on veggies, fruits, and lean protein while staying away from saturated fats, added sugars, and refined carbs is a good rule of thumb and a good place to start.

Get enough physical activity

If your pregnancy doesn’t forbid you to get regular physical activity, try to squeeze as much of it as you can throughout the day. Exercising or even just going for a walk supports the production of happy hormones in your body and regulates the activity of hunger neurotransmitters in your brain. Once again, ask your doctor about the safe options, and keep in mind that any physical activity will also boost your baby’s healthy development.

Get enough sleep

Besides staying active, you should prioritize a good night’s rest. Going to bed on time will also decrease your chances of increased hunger and snacking cravings during the late hours, keeping your body weight under control.

Stay hydrated

Those eight glasses of water a day may seem like a demanding task initially, but once you complete it for a few days, your body will quickly get used to it and start giving you clear signs it’s time for some hydration. Sufficient water intake can also help keep your cravings under control.

Give yourself a break

Pregnancy should be a beautiful and joyful period of your life; don’t make it stressful by beating yourself up to lose weight or start using weight loss supplements. Giving yourself a break every once in a while and enjoying a meal that may not be that nutritious is completely fine, and it can actually help you maintain your weight. Remember that losing weight during pregnancy is not something you should aim for; instead, inspire yourself to eat healthy, nutritious foods. Depriving yourself of everything you like can backfire and get you into a state of overindulging.

Final thoughts

While the use of phentermine under professional medical supervision typically leads to weight loss, pregnant women may not be a perfect match for this drug. Using phentermine during pregnancy may impose a number of risks to the baby and the mother. It’s essential to keep in mind that every pregnant body should grow in size, and if your pounds go a little out of hand, feel free to give us a call to determine safe ways to cure your cravings without weight loss supplements and prevent excessive weight gain.


Nurse Walton


Nurse Walton

Born and raised in Chicago, IL, Chanay received her Practical Nurse licensure and went to work in clinical specialties such as Home Health, Assisted Living, Long-Term Care and Dialysis Centers. Through this work, she realized the importance of diet, nutrition and weight loss among her patients. This led her to open A Better Weigh, Inc. Medical Weight Loss Center in 2009.

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