Can I Use Phentermine While Breastfeeding?

by Ahmed Zayed, MD on April 13, 2024
Last updated on April 13, 2024

Phentermine works like magic for shredding pounds, changing the game for loads of people fighting the tough battle against obesity for way too long. Mix it with eating right, cutting down on snacks, and keeping active, and voila, you see miracles happen.

a newborn baby with mom and dad

But there are some side-effects that should be expected. And there are some medical conditions that prevent the use of Phentermine. One of those is the breastfeeding period, which might be tough for some mothers to hear. You see, Phentermine and breastfeeding simply do not go hand in hand. But can you guess why?

In today’s topic, we decided to share some basic facts about the history and the use of Phentermine, as well as, its truly amazing beneficial effects, but most importantly, today we are here to talk to you why you should say no to the use of Phentermine during pregnancy and breastfeeding.

We sure hope that all of you expecting mothers and breastfeeding mothers are interested to find out more. We hope that by the end of today’s article you will have answers to the questions that have been worrying you and as always, find questions that you can discuss with your doctor. Shall we start?

Phentermine – What is it and why is it used?

It was way back in 1959 when the amazing weight loss drug known as Phentermine first hit the market.

Phentermine was almost instantly approved by the FDA (Food and Drug Administration) and quickly replaced the popular “Rainbow pills” which were used until that moment, and the FDA was more than happy to replace due to the severe side-effects and complications which they were known to cause (1).

Phentermine is available with a doctor’s prescription only. This means that you will not be able to get the original Phentermine product online or at your favorite supermarket. Anything that can be found in such places under the belief that it is the original Phentermine drug should not be bought and used under any circumstances. Phentermine is actually being used to treat mild and more severe cases of obesity and overweight.

In order for your doctor to prescribe Phentermine, the main factor is your BMI (Body Mass Index) being 30 or higher (2). Of course, other factors play a vital role in the decision-making process. In addition, Phentermine is only meant to be used for the maximum period of 12 weeks, or 3 months, due to its highly addictive nature. Phentermine can be used longer than 12 weeks only with a proper pause in between.

Phentermine is a psychostimulant which means that it works by stimulating certain brain areas in order to suppress your feelings of hunger, reduce your appetite, and boost your energy at the same time. But Phentermine is not a magical pill, and it is meant to be used with a certain effort on your side as well. In order to achieve your goal of losing weight, you are meant to follow a balanced, healthy diet and workout on a daily level as a healthy method for losing weight (3).

The potential dangers of using Phentermine

Being approved by the FDA and being prescribed voluntarily by doctors all around the United States, plus the millions of satisfied patients so far, classifieds Phentermine as a generally safe to be used drug.

Yet, the possibility of the potential side-effects should not be excluded. Unfortunately, sometimes, due to known and unknown factors and circumstances, Phentermine has caused unwanted side-effects to develop. And while some of the side-effects are milder than others, the biggest problem with Phentermine is its highly addictive nature. In the following, we will list some of the most common potential side-effects that have been reported over the years.

Keep in mind that this does not mean that you will experience the following side-effects for sure, there is a variety of factors that play a certain role in that process (4). Of course, using Phentermine as instructed by your doctor is the only way to ensure yourself that you are staying as far away as possible from any side-effects.

  • Dry mouth
  • Insomnia
  • Digestive problems – constipation and diarrhea
  • Low libido
  • Irritability
  • Headaches
  • Tremors
  • Dizziness and restlessness

Among the most severe side-effects chest pain, shortness of breath, and addiction have been listed.

If you experience any of these side-effects, please contact the doctor who has prescribed you Phentermine for further instructions. Addiction is, unfortunately, quite common when it comes to Phentermine. That is why Phentermine is strictly advised to be used according to the instructions given by the doctor, and it is only meant for a short-term use no longer than 12 weeks.

To avoid the risk of getting addicted to Phentermine, we highly advise you to keep to your doctor’s instructions and do not interfere with the dosage on your own by any terms. Any questions that you might have about the use of Phentermine can be answered by your doctor at any time. Phentermine is known to interfere with many medications, which is why it is highly important to mention any medication use to your doctor.

Also, discuss any medical conditions, diagnosed and undiagnosed, that you might have with your doctor before you proceed with your use of Phentermine.

Should one use Phentermine while breastfeeding at the same time?

Although we are talking about a drug that most of the time is safe to be used, there are some medical conditions that permit the use of Phentermine.

A few good examples would be hyperthyroidism, a history of heart disease and/or heart attack, a history of stroke, glaucoma, diabetes, etc (5).

These examples also include pregnancy and breastfeeding. If you are currently pregnant or breastfeeding your little one, the chances that your doctor will prescribe you Phentermine are basically zero, and even if he/she does, we advise you not to take it. And here is why…

The FDA has placed Phentermine in three different groups over the years. Phentermine belongs to the X, B, and C group. Let us explain these:

The group X contains a drug which when tested in animal and human subjects, they have shown positive results of fetal abnormalities and even a miscarriage.

The group B contains drugs which failed to provide positive or negative results whatsoever when tested in studies done on animal subjects.

And finally, group C contains drugs which when tested among animal subjects have clearly shown an adverse effect on the fetus, however, human studies are lacking on this topic (6).

Being placed in these three groups, Phentermine has been declared unsafe to be used during the period of pregnancy.

All pregnant mothers are advised against the use of Phentermine during their pregnancy and their breastfeeding period (7). Phentermine should not be used during the period of pregnancy nor during the period of breastfeeding. We have clear medical results that say enough about the use of Phentermine during pregnancy, but what we are lacking are medical studies done on the use of Phentermine during breastfeeding. You see, while medical studies do confirm Phentermine being excreted in the milk which is later used to feed the infant with, there are no medical studies, yet that can confirm how much of Phentermine exactly is being excreted in the human milk (8).

But what we do now is that for a fact, with Phentermine being excreted in the human milk, you are exposing yourself and your little one to the great risks of milk dehydration, increased blood pressure, agitation, tremors, and hyperactivity in the infant, as well as decreased feeding. Basically, by using Phentermine, and following the instructions of regular use, combined with a calorie deficit and regular working out, you are exposing your body to the risk of milk dehydration due to the lack of calories that you are intaking. In addition to that, your little one might show signs of agitation, tremors, and even decreased feeding, which, when you think about it, are all examples of the expected effects and side-effects caused by Phentermine. These, of course, are not effects that you would want to see in a little baby that needs its time, love, and warm milk to grow and develop into a healthy and happy baby. And you would not want to stop producing milk in the period when your little one needs it the most. Of course, there is powdered milk that you can use, but why use it when you are able to produce a much healthier and natural version of it? That is why Phentermine should be discontinued during the pregnancy and the breastfeeding periods. The mother can continue using Phentermine after she has stopped breastfeeding her child.

Any breastfeeding questions that you might have can be answered by your doctor. All in all, although your doctor might decide on prescribing Phentermine, we strongly advise you to talk to your doctor and find another solution for your treatment for obesity/overweight. We would not advise you to ask your doctor on your own to get Phentermine prescribed to you during the period of pregnancy and breastfeeding. Do not expose your loved one to the great risks that this, potentially harmless weight loss drug can cause to it. A breastfeeding mother should continue eating normally, following a well-balanced diet without any sign of a calorie deficit during her breastfeeding period. All breastfeeding mothers should remember to eat regularly and enough to be able to continue producing enough milk as their little one requires it in order to grow. If you are interested in losing weight during the breastfeeding period, we would advise you to take on a workout plan and create a diet plan that will allow you to still have a balanced diet, just without the well-known enemies of the weight loss process such as artificial sugars, fats, alcohol, etc.


If you are currently pregnant or breastfeeding, you might want to think about using some other weight loss method rather than using Phentermine. And yes, even if your doctor has said yes to it, we strongly advise you against it.

You see, when it comes to using Phentermine during the nine months of pregnancy and the breastfeeding period, the potential risks outweigh the potential beneficial effects, making Phentermine unsafe to be used. So as you have learned from today’s article – if you are interested in preserving your little one’s good health and make sure that he/she is growing and developing as it should, you should stay away from Phentermine and consult your doctor on other weight loss methods during this time.

No weight loss is worth it for your child’s good health and proper development. Phentermine will still be there, waiting for you after you have finished breastfeeding your child.


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