Can you take Phentermine while Breastfeeding? (effect on breast milk)

June 16, 2022 |

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No, it is better to avoid taking phentermine while breastfeeding because its safety in nursing mothers is not well researched.

So, you have just brought a little angel into the world, and it is great that you don’t want to wait until your baby weans from breastfeeding to get back into shape.

However, thinking of taking phentermine might not be a great idea to go about your postnatal weight loss.

The reason is that there are no clinical trials and research that may prove the safety of phentermine in nursing mothers. Moreover, phentermine already poses risks of causing certain side effects even in normal individuals, so you and your baby might be more vulnerable to these risks during nursing days.

This article will educate you about the ways phentermine may affect your breast milk and answer all the different questions you might have regarding its safety and efficacy during breastfeeding.

So, let’s get into it without any further ado.

Does phentermine affect breast milk?

Yes, phentermine may affect breast milk. Nonetheless, your healthcare provider may provide you with better advice by weighing the importance drug to you and its effect on your breast milk to your nursing baby.

woman breastfeeding baby

Although scientists have yet to research whether phentermine is excreted in the milk of nursing mothers or not, they did investigate the effect and release of amphetamine on lactating women.

Phentermine is pharmacologically and chemically related to amphetamine, so it may be hypothesized to have similar effects to it.

The critical structure of phentermine is quite similar to amphetamine, and it basically has a methyl group on the amphetamine’s alpha carbon.

Moreover, both these compounds are stimulants, and the difference lies in the magnitude of stimulation since amphetamine is a more potent stimulant than its counterpart.

As there is not much research available on phentermine so, keeping in view the similarities between the two, I will provide you with a summary of the available research on amphetamine in this section because it may help you to assume what effect phentermine will have on your lactation ability and breast milk.

They say that what you eat affects your breast milk, and thus, most drugs and medications have been found to appear in breast milk, even if they do in small or safe amounts.

Similarly, amphetamines like methamphetamine were also found to get secreted in breast milk.

And thus, the same may be hypothesized for phentermine as well. Nonetheless, the drug information on phentermine does not clearly mention its effect on nursing mothers due to lack of evidence, but it is contraindicated during nursing and pregnancy.

Moreover, a combination of phentermine and topiramate is included in category X of the FDA because it may induce fetal abnormalities and miscarriages in both humans and animals and is found to be distributed in breast milk.

Moreover, recent studies suggest that amphetamines suppress the serum prolactin in most women.

Prolactin is a hormone that stimulates milk production in women. However, this prolactin suppression did not have any adverse effect on the breastfeeding ability of mothers who had an established lactation.

But, amphetamines are expected to affect the breastfeeding ability of mothers whose lactation is not well established.

Nonetheless, experts discourage the therapeutical use of amphetamines in nursing mothers, so you need to be careful with regard to phentermine as well and strictly follow your doctor’s advice in this regard.

Moreover, if you look at this topic by considering the weight loss potential of phentermine, then users have reported an average weight loss of 5 Ibs in one week by taking 37.5mg of phentermine.

But in contrast, fast weight loss during breastfeeding may decrease your supply of milk, and this is why nursing mothers are recommended to lose only a pound and half (670 grams) per week as it may not affect their milk supply that much.

Your doctor may adjust your phentermine dosage in case its prescription is unavoidable. And you will also need to monitor and report your well-being and any changes in your milk supply while on prescription.

How long after phentermine can I breastfeed?

You should wait at least 24 hours and at max a week before nursing your child after phentermine.

The effect of phentermine on breastfeeding is an under-researched topic.

I already mentioned in the above section that a combination of phentermine and topiramate is secreted in breast milk. However, no specific studies may prove whether phentermine alone will be secreted in breast milk or not.

And for the same reason, its secretion in breastmilk could not be quantified, making it hard to say anything with surety about how much time breastfeeding should be withheld after taking phentermine.

Theoretically, it is recommended that mothers withhold breastfeeding for 24-36 hours after taking drugs and medicines.

However, a study that quantified the concentration of amphetamine in breast milk found that mothers should restrain from breastfeeding their babies for 48 hours after using amphetamines for recreational purposes.

Moreover, a mother asked how long she should wait before going back to breastfeeding after taking phentermine.

And according to Dr Anil’s answer to her question, you may continue to breastfeed your baby after a week of discontinuing phentermine. The reason is that the half-life of phentermine is 16 to 31 hours, and it may take around 3.5 to 6.5 days to be eliminated from your body completely.

Anyone took phentermine while breastfeeding? (stories)

Since there is a lack of scientific evidence to support the safe use of phentermine in nursing mothers so, I headed over to different forums to look at what the user experience can tell us in this regard.

And although there are some nursing mothers who took the drug, most doctors still recommend that it is better to avoid it.

  • Testimonial #1

In reply to a question asked by ‘Kga93 on about whether anyone has ever taken phentermine while nursing, ‘Kia93mommy4’ wrote that she took phentermine with her nursing one-year-old and saw no side effects, so it worked well for them both.

  • Testimonial #2

‘Nikki1220’ is another user who wrote on MedHelp that she took phentermine after 4 months of giving birth to a baby upon the doctor’s prescription.

She didn’t specify the effect of the prescription drug on breastfeeding but did write that it helped her lose 11 pounds in the first two weeks.

  • Testimonial #3

‘Flowermom20’ started this thread on this forum by sharing that her doctor recommended that she try phentermine for weight loss (her doctor didn’t know she was breastfeeding by then).

But since there are no safety studies to support its use in breastfeeding women, she asked if any nursing mothers had tried taking it before and how it affected their babies.

The users who replied advised her against it, but their opinions were based on their experience of taking the drug in normal conditions.

One of the users found it too strong, and another user shared that it affected her eyesight. An ICU nurse shared that she has witnessed cases of heart and lung failure and deaths caused due to complications in pulmonary hypertension caused by this medication.

What happens if you take phentermine while breastfeeding?

Phentermine works to suppress appetite, and it will show the same effect if you take it while breastfeeding, which may help you to shed a bunch of calories. But as mentioned above, losing a lot of weight may affect your milk supply.

Moreover, phentermine may also appear in your breastmilk. But its concentration and safety cannot be claimed with scientific evidence as of yet.

Can you take any weight loss pills while breastfeeding?

No, doctors don’t recommend taking weight loss pills unless their prescription becomes extremely important.

Breastfeeding your baby already helps to burn calories, and instead of looking for ways to cut down on calories, CDC states that well-nourished nursing mothers require an additional 330 to 400 kilocalories (kcal) per day than their normal intake while breastfeeding.

Doctors recommend avoiding weight-loss pills because they may contain herbs, caffeine, and other ingredients that may be harmful to the nursing baby.

Some risk-less ways in which you may lose some weight while breastfeeding is by doing exercise, pursuing a low-carb diet, keeping well hydrated, and resting.

Nonetheless, suppose it becomes extremely important to take weight-loss pills. In that case, some safe and effective options you have are an all-in-1 postnatal fat burner, Brilliant Garcinia Cambogia, ProbioSlim, envy nighttime fat burner, and plexus block.


To conclude, it is best to keep away from phentermine while breastfeeding.

One reason for this is that it lacks scientific studies and abundant user experience to support its safety in nursing mothers.

Another reason is that breastfeeding is already going to help you shed weight, and you don’t need to speed up this process with phentermine.

However, as much as being underweight will affect your milk supply, so will being overweight affect it.

So, unless and until your doctor recommends any weight loss pills, avoid using them while breastfeeding.

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