The Effects of Taking Diet Pills While Pregnant

It's best to avoid taking any OTC or prescription weight-loss pills while pregnant.
Image Credit: dragana991/iStock/GettyImages

Weight gain is a natural part of pregnancy, so there's no need to turn to diet pills to counteract your growing body. In fact, taking weight-loss supplements when you're pregnant can put you and your baby at risk. So, how exactly can diet pills affect pregnancy (including the early stages)?


First things first, weight-loss supplements claim to burn fat, curb appetite, speed metabolism or improve nutrition to help you shed pounds, according to the Cleveland Clinic.

Video of the Day

These over-the-counter (OTC) products are not approved by the U.S. Food and Drug Administration (FDA), per the Mayo Clinic. In fact, there's little scientific evidence to show they're effective at all, which is why products like herbal supplements and flat-tummy pills do not typically work.


And not only are OTC supplements usually ineffective for weight loss, but some of these products can harm your health due to side effects and hidden ingredients, according to the Mayo Clinic. In other words, no, you can not safely take weight-loss pills while pregnant (or otherwise, really).

There are also prescription weight-loss pills — like phentermine — that your doctor may prescribe if you have obesity, per the Mayo Clinic. While this drug is FDA-approved and can support weight loss, you can't take phentermine while pregnant because it may not be safe for you or your baby.


Here's how diet pills can affect early pregnancy and beyond, diet pills' side effects, plus what to know if you got pregnant while taking phentermine.


Talk to your doctor before taking any supplements while pregnant (including non-weight-loss products, like fiber supplements or digestive enzymes) to make sure they're safe for you, per the Mayo Clinic.

They Can Mess With Your Heart Function

Increased blood pressure and heart rate are two frequent side effects of many diet supplements, according to the National Institutes of Health (NIH). This is also true of phentermine — increased heart rate is one of the most common side effects of the prescription drug, per the Mayo Clinic.


High blood pressure and rapid heart rate are not ideal for anyone, pregnant or otherwise. But if you're pregnant, chronic high blood pressure can put you at risk for conditions like preeclampsia and stroke, according to the Centers for Disease Control and Prevention. It can also put your baby at risk for preterm birth and low birth weight.

As a result, taking OTC weight-loss supplements or phentermine while pregnant is not recommended.




Pregnant or not, talk to your doctor before trying any weight-loss supplement to make sure it's safe for you. This is particularly important if you already have an underlying health condition like high blood pressure, diabetes, and liver or heart disease, per the NIH.

They Can Cause Other Side Effects

Diet pills can also affect early pregnancy and beyond (including if you take weight-loss supplements while breastfeeding) because they can cause side effects that may harm you or your baby, according to the Cleveland Clinic.

Per the NIH, products like herbal weight-loss supplements, diet pills and flat-tummy gummies can have side effects like:


  • Headaches
  • Difficulty sleeping
  • Muscle or bone pain
  • Increased heart rate
  • High blood pressure
  • Nausea
  • Vomiting
  • Diarrhea
  • Constipation
  • Abdominal cramps
  • Gas
  • Heartburn
  • Vertigo
  • Weakness
  • Anxiety
  • Jitteriness
  • Kidney stones

When it comes to phentermine and pregnancy specifically, the drug can also cause other side effects besides increased heart rate. Per the Mayo Clinic, these issues may include:


  • Tingling or prickling feeling in your hands or feet
  • Dry mouth
  • Trouble sleeping
  • Nervousness
  • Constipation

Can You Take Diet Pills While on Birth Control?

OTC diet pills are typically ineffective at best and dangerous to your health at worst, per the Mayo Clinic. As a result, it's best to avoid them altogether and instead lose weight safely and sustainably by eating a balanced diet and exercising regularly.

They Can Lead to Organ Damage

Although rare, taking diet pills can sometimes cause severe side effects like organ problems, according to the Mayo Clinic.

For instance, products that contain ingredients like hydroxycitric acid and certain green tea extracts have been linked to liver damage, per the NIH. What's more, the hydroxycitric acid in particular shows little to no effect on body weight.


They Can Contain Harmful Ingredients

Some diet pills are made of ingredients that you're supposed to avoid during pregnancy.

For instance, many supplements contain caffeine, per the NIH. It's recommended to keep your caffeine intake low during pregnancy (that is, under 200 milligrams per day) to avoid passing the substance — and caffeine's effects, like increased heart rate and blood pressure — to your baby, according to the Cleveland Clinic. Caffeine can also contribute to premature delivery and low birth weight.


And because OTC weight-loss products aren't FDA-regulated and don't always list dosage information, you run the risk of overloading yourself and your child with caffeine.

This is also true of herbal supplements — even though they claim to include natural ingredients, these products and their contents aren't actually regulated, according to the Mayo Clinic. As a result, these supplements (like Slimvance, for instance) aren't necessarily safe, so it's best to avoid them if you're pregnant.

Another ingredient in some weight-loss formulas — 5-Hydroxytryptophan — is not recommended during pregnancy, as it may not be safe for your baby, according to Mount Sinai.

Certain products may also contain prescription drugs without listing them on the label, according to the Mayo Clinic, which may lead to unanticipated side effects that can potentially harm you or your child.

Losing Weight Can Harm Your Baby

Taking diet pills for pregnancy weight is not recommended, as you're gaining that weight for a reason.

Indeed, most people gain between 25 and 35 pounds during pregnancy, particularly after the first trimester, according to the U.S. National Library of Medicine. This weight gain is the result of your growing baby, placenta, breast tissue and increased fat stores, fluid and blood supply to fuel you and your child.

Trying to cut these added pounds — particularly by taking an OTC supplement or phentermine while pregnant — can thus jeopardize you and your baby's health.


If you have overweight or obesity when you become pregnant, it may be appropriate to lose some weight during your pregnancy, per the Cleveland Clinic. However, this does not mean you should turn to OTC or prescription weight-loss pills — instead, talk to your doctor about the best way to find a healthy pregnancy weight.

There's not much scientific evidence to show if there are risks to taking phentermine in pregnancy.


But the drug is frequently combined with another medication called topiramate (brand-name Qsymia), according to the Mayo Clinic. Topiramate has been linked to a higher risk of having a baby with a cleft lip, per an October 2014 review in ​American Family Physician​.

And even though this condition is associated with topiramate, it's still best not to mix pregnancy and phentermine.

What Happens if You Took Phentermine and Didn’t Know You Were Pregnant?

Sometimes it's impossible to avoid taking phentermine during the first trimester of pregnancy: For instance, you may have been taking the drug as prescribed before learning that you were expecting.

It's not clear if phentermine alone is linked to pregnancy complications or birth defects, but if you accidentally took phentermine while pregnant, stop using the drug and alert your doctor.

One small 2012 study in ​Neuroendocrinology Letters​ found that there was no difference in pregnancy outcomes for people who took appetite suppressants like phentermine while pregnant compared to those who did not.

But one older March 2002 study in ​Teratology​ found that people who took a combination of phentermine and fenfluramine during the first trimester of pregnancy were at higher risk for gestational diabetes compared to those who did not.

Fenfluramine has since been taken off the market because it was linked to heart abnormalities, though, so more research is needed to better establish the connection between this pregnancy complication and phentermine alone.

Still, the takeaway is to play it safe and speak to your doctor to avoid any potential complications.




Report an Issue

screenshot of the current page

Screenshot loading...