What Are the Side Effects of New Weight Loss Medications?

A study published in 2023 in the medical journal JAMA found that people who take these medications may be at an increased risk for pancreatitis (inflammation of the pancreas) and gastroparesis, sometimes called stomach paralysis because the stomach can’t empty.

Individuals have reported hair loss when taking these drugs, as well as aspiration (when food or liquid enters the airway) when sedated for surgery, likely due to the delay in stomach emptying caused by the drugs.

Suicidal ideation has been associated with these medications; however, in recent studies, researchers found no clear relationship.

Meds may lessen cravings, improve heart, kidney, brain health

Not all of the reported side effects of GLP-1 medications are bad. Accumulating research suggests that many patients experience added health benefits.

Fewer cravings

Some patients taking the drugs say many of their cravings — be it for alcohol, shopping or sugar — subsided. 

“Cravings develop from a reward system in the brain,” says Chetna Bakshi, M.D., a bariatric surgeon at Northwell Health’s Syosset Hospital in New York. These medications, she says, seem to have an effect on that reward system. “I have had patients tell me, for example, ‘I used to crave sweets all the time. Now I don’t care. I don’t need to eat a cookie every day being on these medications,’ ” Bakshi says.

“That’s the biggest thing of how these medications work,” Levy adds. “They quiet the noise in your brain.”

Heart health benefits

In a large clinical trial, researchers found that semaglutide, the active ingredient in Ozempic and Wegovy, can reduce the risk of heart attacks and strokes by 20 percent in adults with heart disease and obesity. These results, published in December 2023 in The New England Journal of Medicine, led the U.S. Food and Drug Administration (FDA) to approve Wegovy for a new indication: to reduce the risk of serious heart problems in adults with overweight or obesity issues.

“Wegovy is now the first weight loss medication to also be approved to help prevent life-threatening cardiovascular events in adults with cardiovascular disease and either obesity or overweight,” John Sharretts, M.D., the director of the division of diabetes, lipid disorders and obesity in the FDA’s Center for Drug Evaluation and Research, said in a March 2024 news release.

“This patient population has a higher risk of cardiovascular death, heart attack and stroke. Providing a treatment option that is proven to lower this cardiovascular risk is a major advance for public health,” he added.

A study published Feb. 5 in the journal Hypertension found that tirzepatide, the active ingredient in Mounjaro and Zepbound, significantly lowered the systolic blood pressure (the top number in a blood pressure reading) of nearly 500 adults who had obesity and took the medication for about eight months. The reduction ranged from an average of 7.4 mm Hg to an average of 10.6 mm Hg, depending on the dose of medication. 

“Although tirzepatide has been studied as a weight loss medication, the blood pressure reduction in our patients in this study was impressive. While it is not known if the impact on blood pressure was due to the medication or the participants’ weight loss, the lower blood pressure measures seen with tirzepatide rivaled what is seen for many hypertension medications,” lead study author James A. de Lemos, M.D., a professor of medicine at UT Southwestern Medical Center in Dallas, said in a news release. 

Cutting kidney risks

The results of a clinical trial of more than 3,500 participants, published May 24 in The New England Journal of Medicine, suggest that a weekly dose of semaglutide can reduce the risk of serious kidney complications in patients with type 2 diabetes and chronic kidney disease. Participants also saw cardiovascular benefits, and the trial was stopped early due to the successful outcomes.

“We would be saving kidneys, hearts and lives in this population by making this drug available to them and that’s quite extraordinary for one treatment to be able to do,” lead study author Vlado Perkovic, a nephrologist at the University of New South Wales, Sydney, said in a statement.  

Protecting the brain

Results from a phase 2 study presented at the 2024 Alzheimer’s Association International Conference suggest that liraglutide (Victoza, Saxenda), which is considered an older GLP-1 medication, may help protect the brain and slow cognitive decline.

The study included 204 people with mild Alzheimer’s disease; half of the participants received liraglutide and half received a placebo. Researchers found that those who received liraglutide had a slower loss of brain volume, including in areas that control memory, learning, language and decision-making. The liraglutide group also had a slower decline in cognitive function over one year, compared with those who got the placebo.

“The slower loss of brain volume suggests liraglutide protects the brain, much like statins protect the heart,” lead researcher Paul Edison, M.D., a professor of science at Imperial College London, said in a news release. “While further research is needed, liraglutide may work through various mechanisms, such as reducing inflammation in the brain, lowering insulin resistance and the toxic effects of Alzheimer’s biomarkers amyloid beta and tau, and improving how the brain’s nerve cells communicate.”

Weigh the risks of side effects

Despite reports of serious side effects, Levy says these medications have a pretty solid safety record. (Some GLP-1 agonists have been around for nearly two decades.)

A lot of people who experience the common side effects tend to feel better as they continue on the medications, not worse. Plus, intermittent treatments can bring relief. For example, MiraLAX can help with constipation, Levy says.

Some of the side effects may not be a result of the drug but the weight loss itself — Levy says hair loss is “incredibly common” in people who lose a lot of weight — or they could be due to an underlying disease. Ozempic and Mounjaro are approved for diabetes, which is the most common known cause of gastroparesis (stomach paralysis), according to the National Institute of Diabetes and Digestive and Kidney Diseases. In some studies, it affects up to half of people with type 1 and type 2 diabetes.

These diabetes and weight loss medications are not for everyone. People who have a history of pancreatitis should discuss the risks with their doctor before starting the drugs. Bakshi says patients who have medullary thyroid cancer or a family history of it should not take them, because of the potential risk of thyroid C-cell tumors. 

What’s more, research suggests that most people regain much of the weight they lost when they stop taking the medications. One study, published in the journal Diabetes, Obesity and Metabolism, found that participants gained back two-thirds of the weight they lost a year after stopping Wegovy. 

Talk to your doctor

Bottom line: Have a conversation with your health care provider before starting these medications. “Side effects are always important to know, and [patients should] understand that there’s no miracle drug,” Bakshi says. “Everything comes with a risk; everything comes with complications.”  

Reports of aspiration underline the need for medical supervision while taking the medications, Levy says. The American Society of Anesthesiologists suggests withholding GLP-1 medications before elective surgery to reduce the risk of complications, and this is something your doctor can help with, should you have an upcoming operation.

Some people take these medications without ever making a trip to see their doctor, new reports show. The FDA says semaglutide, the active ingredient in Ozempic and Wegovy, is illegally marketed online. The agency warns that “these drugs may be counterfeit, which means they could contain the wrong ingredients, contain too little, too much or no active ingredient at all, or contain other harmful ingredients.”

“It could certainly lead to complications if patients are not being screened properly and counseled properly,” Levy says. “So I think that’s the big takeaway.”

Editor's note: This story, originally published Jan. 17, 2024, has been updated to reflect new information.