Phentermine and Pregnancy: Safety and Side Effects

Losing weight during pregnancy is almost never going to be something your physician asks you to do. While there are adverse effects in pregnancy related to obesity, a moderate weight gain is required^[1] for a good fetal outcome. Thus, weight loss isn’t good for your unborn baby, and when you factor things like weight loss drugs into the mix, the matter only becomes more dangerous for you and your future child. 

The potential risks of phentermine may very well undermine the potential “good” that it can do for your weight loss goals—mothers who took phentermine while in their pregnancy have been shown to put themselves at a significantly increased risk for many issues. Heart problems, high blood pressure, and birth defects have all been associated with phentermine while pregnant. True, phentermine’s adverse effects have also been cited for even women not pregnant, but when added to the dynamic and unique physiology of pregnancy, there are considerable added, pregnancy-associated risks.
No mother needs to lose weight by using phentermine during pregnancy—there will be plenty of time for phentermine and any other weight loss medication under the sun after you’ve successfully delivered your baby. Here are a ton of reasons to put your focus squarely on the health of your growing child during this critical period of development.

What Is Phentermine?

According to the Food and Drug Administration (FDA), phentermine is “controlled^[2],”  a schedule IV substance^[3] used as an appetite suppressant and as an aid to obesity management. The technical term for this type of weight loss drug is a sympathomimetic amine anorectic, which simply means that it’s designed to restrict calories by making the patient less likely to want to eat, an effect you see with amphetamines, another sympathomimetic.

It is often prescribed in a combination formulation with another anorexiant, topiramate, where the anorectic effects become far more powerful than taking phentermine or topiramate alone^[4]. However, both phentermine and topiramate–and certainly their combination–shouldn’t be taken during pregnancy.
Phentermine has earned its place as a schedule IV drug in 1959 because it has been shown to present a very low-risk threshold for addiction and abuse, but not zero-risk; hence it’s being controlled. This does come with the caveat that the original cocktail was not meant to be taken long-term, but, rather–instead– as a short-term adjunct (up to 12 weeks). It’s meant for those struggling with exogenous obesity, a condition caused by overeating alone^[5].

How Does Phentermine Work?

Phentermine does its work^[6] by releasing noradrenaline from the presynaptic vesicles in the brain’s lateral hypothalamus, stimulating the production of beta2-adrenergic receptors, increasing norepinephrine and dopamine as well as influencing one’s serotonin levels.

It may also inhibit neuropeptide-Y in the brain, an important signaling compound^[7] for satiety (feeling “full”) used to self-regulate appetite and energy expenditure. All of these factors come together in the body, resulting in a much higher resting metabolic rate in addition to the drug’s anti-appetite effect. 

Despite the fact that it has been shown to be effective as far as appetite suppressants go, this amphetamine derivative may actually be incredibly dangerous if you’re pregnant or breastfeeding due to the already-precarious cardiovascular dynamics at work in pregnancy.

Can You Take Phentermine While Pregnant?

As far as phentermine and fertility are concerned, taking phentermine will not significantly reduce your likelihood of conceiving if you and your partner are interested in having a baby. With that being said, however, if you are trying to conceive, you should discontinue your use of phentermine immediately for the sake of the health of your future child.

Because phentermine exhibits pharmacologic activity similar to amphetamine stimulants, it may cause irreversible harm to a developing fetus. Because amphetamines can be passed from the mother to a nursing baby through breast milk, breastfeeding mothers are also advised to avoid phentermine use.

For these reasons and more, the FDA advises that any pregnant or breastfeeding woman avoid phentermine use under any and all circumstances. Officially, this is because losing weight during pregnancy is rarely necessary; typically, it is more likely that the rate at which you gain weight is what needs to be controlled. However,  if it is necessary to lose weight, there are safer, drug-free ways of meeting the needs of yourself and your child. If you find yourself pregnant while using phentermine, discontinue your use immediately.

What could happen to your unborn child if exposed to this drug during the first trimester? Actual developmental abnormalities are rare (but not zero), and they are only more likely if you’re taking topiramate. The biggest risks are the dangers to your cardiovascular system added to how pregnancy already affects it, meaning the longer you take phentermine (and/or topiramate) in pregnancy, the bigger the danger. You must remember that you are the incubator, and if the incubator has problems, so will the fetus she’s carrying. If you didn’t know you were pregnant and are currently taking phentermine, discontinuing your usage is the best action. There’s a good reason why pharmaceutical weight loss products are not advised for new and expecting mothers.

Risks for Mothers: Phentermine While Pregnant

Long-term phentermine usage isn’t the problem—using the drug while pregnant or breastfeeding is what expecting mothers need to worry about, especially first-trimester exposure.

Some of the most dangerous reasons to leave phentermine behind you after becoming pregnant include all of the following:

• Birth defects beyond one’s ordinary background risk
• Fetal stroke^[8] and brain hemorrhage
• Global developmental delay
• Bilateral porencephalic cysts^[8]
• Neural tube defects^[9], a condition under which the spine isn’t able to constitute itself fully (spina bifida is one tragic example)
• Cerebral palsy after birth
• Higher-than-usual birth weight and head circumference
• Preterm labor; preterm delivery

The pregnancy information on the pharmaceutical label is, unfortunately, spotty with information for expecting mothers—as with any type of drug, consulting your doctor is recommended above all else for pregnant and breastfeeding women.

Phentermine and Breastfeeding

Can phentermine pass through to your infant through breastfeeding? A trial conducted on mothers using amphetamines recreationally confirmed that this type of substance makes its way to your child^[10] through the milk you share. Phentermine itself has not yet been studied extensively in this way, but many experts believe that it may, indeed, also be subject to this evidence-based finding.

Breastfeeding while taking phentermine has been shown to cause a myriad of negative outcomes for both mother and baby— tremors, agitation, difficulty sleeping, and even a reduction in your child’s interest in feeding regularly; these may all disrupt one of the most important periods of bonding in a mother and child’s life-long relationship.

If you were able to discontinue phentermine use before becoming pregnant, you’re already in the clear as far as this risk factor is concerned. 

How Long Should You Wait to Take Phentermine Before Breastfeeding?

Few clinical trials have been conducted on how long to wait after using phentermine before breastfeeding your child. As with any potentially dangerous dietary drug, it’s always best to take it off the table entirely if you have a new child to feed biologically. Everything that you eat, they eat, too—food, alcohol, and, yes, even phentermine. However, this may be a moot point since it is assumed you’ve discontinued phentermine before pregnancy and, thus, before breastfeeding. 

Nevertheless, the elimination half-life of phentermine is anywhere from around 19 to 24 hours^[11], after which the majority of the drug, 70 percent to 80 percent, has already been metabolized by the liver and excreted through the urinary tract. In theory, if phentermine use has lapsed beyond this duration of time, you’re much less likely to convey it to your newborn infant through your breast milk. But are you going to be breastfeeding less often than every 19-24 hours? Likely, not.

The study above recommends at least 48 hours before breastfeeding after amphetamine use, but, to be fair, the study was conducted using recreational amphetamines, not phentermine. Thus, since phentermine’s chemistry is related to amphetamines, it still counts.

In any case, it’s better to err on the side of caution—avoid phentermine entirely if possible. If you have taken it, wait at least two days before exposing your child to it through expressed breast milk.

Other Side Effects of Phentermine

Overdosing on phentermine would be extraordinarily unusual, but taking too much of it can certainly put you in some amount of peril^[12]. These may include withdrawal symptoms if your phentermine usage is disrupted for any reason.

Expecting mothers aren’t the only ones who may suffer when taking phentermine to lose weight while your pregnancy. The adverse outcomes anybody may experience after too much phentermine include

• Restlessness
• Tremors
• Hyperreflexia, ultra-sensitive reflexes
• Heavy breathing
• Mild confusion
• Hallucinations 
• Panic and anxiety

• Paresthesia, a pins-and-needles sensation
• Dysgeusia is a sensory perception disorder of the taste buds
• Dry mouth
• Constipation or diarrhea
• Insomnia
• Fatigue
• Mental depression
• Decreased libido

Cardiovascular-related side effects may also pose some risk to the especially vulnerable:

• Tachycardia
• Arrhythmia
• Pulmonary hypertension
• Hypertension
• Myocardial infarction
• Circulatory collapse

No drug designed to promote weight loss is without its adverse outcomes and withdrawal symptoms. While phentermine has not yet actually been pulled off the market by the FDA, there are significant differences between weight reduction with the help of pharmaceuticals and an obesity diagnosis with treatment done the natural way.

Good food, moderate exercise, and a more mindful way of living will all be commitments that your future child will thank you for.

What If You Want to Lose Weight During Your Pregnancy?

This is tricky. So tricky that it requires the help of healthcare professionals. As stated before, pregnancy is a very complicated alteration of your body’s processes. There’s a lot of “book knowledge” that must be involved to safely pull off weight loss, so you should not try it alone. Instead, you should incorporate the help of your doctor/midwife, dietitian, and nutritionist who specializes in pregnancy.

Does Phentermine Pose a Risk to Pregnancy Outcomes?

Is phentermine an effective fat burner? Perhaps, but you should never try to lose weight during pregnancy. Instead, keep your eyes on the prize and provide your body with everything that it needs to support the growth of your child during this irreplaceable period of development. 

While obesity during pregnancy may leave you vulnerable to conditions like high blood pressure, gestational diabetes, and other pregnancy-related complications, few doctors will ever advise a pregnant woman to actively seek to lose weight, especially through the use of appetite suppressants like phentermine. 

Alternatively, in order to prevent any adverse effects from influencing the development of the embryo, it’s recommended that a woman lose any extra weight before even becoming pregnant, to begin with. Dieting while pregnant, in the most extreme cases, may lead to anything from premature delivery to spontaneous pregnancy loss; maternally, it can play havoc with your blood sugars and risk injury to you from passing out.

This is to say nothing about some of them. Even more extraordinary l complications associated with phentermine during pregnancy. The withdrawal symptoms alone are more than enough to put many women off if they plan on becoming pregnant imminently; withdrawal is never pleasant, and anything unpleasant is always worse during pregnancy. To ensure positive pregnancy outcomes in the future, it’s always a safe bet to abstain from drugs like phentermine.

Take it from us (and the Food and Drug Administration): with a new baby on the way, your body mass index should be the last thing on your mind. Increased risk to your baby is never worth it—there will be plenty of time to lose weight after giving birth. You’ll even have a brand-new buddy to help you kick off your weight loss journey in style.

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