Yes, scientists test drugs in clinical trials before they come to market so we can have a pretty good idea of the risks and benefits, but once they’re prescribed widely throughout the population, new risks inevitably emerge. For medications that treat uncommon conditions, it can take many years for us to gain a true understanding of the drug’s risks, but for medications like COVID vaccines and weight loss drugs that have been prescribed to millions of people within months of FDA approval, the information comes at us much faster.
Not to mention, the manufacturers are currently testing them on a host of other ailments such as liver disease, polycystic ovarian syndrome (PCOS), and even Alzheimer’s disease. Our Weight Loss Drug Side Effect Tracker is here to help you make sense of our evolving understanding of the side effects of weight loss drugs such as Wegovy, Ozempic, Mounjaro, and Zepbound. We’ll be updating it as new information emerges about how these drugs—and those poised to hit the market—can help or harm us.
To learn more about the basics behind the new surge of weight loss drugs and how they work, read MedShadow’s The Side Effects of Wegovy and Ozempic and Obesity: Causes, Risks, Weight Loss Treatments and Side Effects.
There are many reasons that we continue learning new safety information about old drugs. First, as mentioned above, as more and more people are treated in real-world scenarios, rare side effects that might not have shown up in the clinical trial population become more clear.
But also, the participants of clinical trials tend to be healthier than the overall population. Scientists don’t want other conditions or other drugs that an individual is taking to interfere with their understanding of how the new drug works, so they’ll study patients who have only obesity or only diabetes, when in reality, most people with those conditions in the general population may also have multiple conditions at once like obesity with arthritis, endometriosis, depression, cardiovascular disease and more. Sometimes that data gets messy, and it can take a lot of additional research to understand.
Here’s what we know, so far, about the benefits and side effects of the new weight loss drugs coming to market. It’s important to note that unless otherwise noted, all of the information below is about the versions of the drugs mass produced and sold by the original manufacturers. Because of shortages, many people may use compounded versions made by specialized pharmacies aiming to replicate the original drugs. These versions could have unexpected side effects. We’ll be updating this page regularly as more information comes out.
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Gastrointestinal Side Effects of Weight Loss Drugs
These were some of the first side effects documented in the clinical trials. Studies noted that 62% to 74.2% of patients who took Wegovy in clinical trials experienced nausea, diarrhea, or vomiting. Some even found they forgot to drink water and became dehydrated. In many, though not all, cases, people say these side effects improved after six weeks on the drug.
December 18, 2023: Reports of people requiring hospitalization and intravenous fluids to manage nausea and vomiting caused by taking too much semaglutide increased. Some people misunderstand the dosing; others took unregulated compounded semaglutide that ended up being higher doses than typically prescribed.
October 2023: A study found that people taking Wegovy or Saxenda (liraglutide) were at higher risk not only for intestinal obstruction, but also gastroparesis (delayed emptying of the stomach) and pancreatitis (inflammation of the pancreas that can cause vomiting and fevers,) than those taking Contrave, an older weight loss drug that works differently.
September 22, 2023: Manufacturer of Ozempic adds ileus (a blockage of the intestines) to its label as a possible risk. The labels for Wegovy and Mounjaro already listed this danger.
March 28, 2022: Manufacturer of Ozempic adds risks of gallbladder problems to its label. Symptoms include stomach pain, fever, jaundice and clay-colored stools.
September 2021: Some researchers are drawing attention to the fact that one of the side effects of Wegovy and Ozempic is that they may increase your risk for an intestinal obstruction. That’s when food is blocked from making it all the way through your digestive tract, and you may need surgery to correct it.
Psychiatric Side Effects of Semaglutide
The clinical trials for these drugs did not raise the concern of psychiatric side effects, though several previously-approved weight loss drugs that work through different mechanisms do carry warnings regarding mood changes and suicidal ideation.
January 5, 2024: Researchers did not find evidence of increased risk of suicidal ideation with the new drugs after reviewing medical records of 240,618 individuals with obesity or diabetes who took semaglutide or medications that work differently to treat obesity or diabetes. The risk of suicidal ideation for those taking semaglutide for weight loss was 0.11% if they had never had the ideations before and 7% if they had a history of suicidal ideations. For those prescribed different medications for weight loss, the risks were 0.43% and 14%, respectively. The FDA is continuing to investigate.
November 28, 2023: A study shows that people who take semaglutide or Mounjaro (tirzepatide) lowered their alcohol consumption.
November 3, 2023: The New York Times draws attention to the fact that psychiatrists are starting to prescribe semaglutide to counteract the weight gain often seen as a side effect of antipsychotic medications and some antidepressants. Experts say this may be useful for those that need these medications, but also warn that little is known about combining psychiatric medications with semaglutide, and that treating a side effect with another drug can be the start of a dangerous prescription cascade.
September 28, 2023: Reuters investigation finds that the FDA received 265 reports of suicidal ideation or behavior among patients taking Ozempic, Wegovy or Mounjaro since 2010. FDA and European Medicines Agency (EMA) plan to investigate.
Cancer Risk
Early studies of semaglutide injections in animals suggested that the drugs could cause certain types of thyroid tumors, and the manufacturers currently warn against taking semaglutide drugs if you have a family history of medullary thyroid cancer or multiple endocrine neoplasia type 2. So far, the risks have not been seen in humans.
January 4, 2024: Researchers find that people who took semaglutide and similar drugs for type 2 diabetes did not have a higher risk of pancreatic cancer than people treated with other diabetes medications, at least within the next five to seven years from when they started taking the drugs.
May 8, 2023: The EMA says it will look into whether semaglutide raises the risk of thyroid cancer. The label currently states that those at risk of medullary thyroid cancer, specifically should not take the drug. So far, it is unknown whether the drugs are associated with a higher risk of thyroid cancer.
Effects on Surgery
December, 19, 2023: Researchers reviewed medical records of nearly 10,000 patients with diabetes who had hip replacement surgeries. Almost all (more than 90%) of the participants were also taking metformin, and almost half (46-47%) were using insulin. Those taking semaglutide to treat diabetes had fewer joint infections and were less likely to go back to the hospital over the next 90 days than those who weren’t using the drug. The scientists point out that this may be because of the drug’s ability to control blood sugar or its direct effects on our immune cells. It’s important to note that the study had several limitations. First, it’s an observational study, meaning the researchers were unable to control who got semaglutide and who didn’t. They state that it’s possible that many of those who were able to access semaglutide had higher socioeconomic status than those who didn’t, which could have influenced outcomes, but we don’t have that data. We also don’t have data about other illnesses or how well the diabetes was controlled in each patient.
June 4, 2023: Researchers reviewed medical records of more than 40,000 people who diabetes and obesity and underwent total knee replacements and found that those taking semaglutide were less likely to have joint infections, sepsis, and hospital readmissions but were more likely to have heart attacks (1.0% in the semaglutide group and 0.7% in the non-semaglutide group), kidney injuries (4.9% in the semaglutide group compared to 3.95 in the non-semaglutide group), pneumonia (2.8% vs 1.7%) and low blood sugar (1.9% vs 1.2%) than those who weren’t taking semaglutide.
Efficacy
When semaglutide was first approved, not for weight loss but only to treat diabetes, clinical trials had shown modest weight loss in many of the patients (about eight pounds over 30 weeks). In a clinical trial of Wegovy, patients who used the drug while making healthy changes to their diets and physical activity lost about 6% of their body weight in the first 12 weeks, 10% after 20 weeks, and 15% at the one year mark. They started to plateau in weight loss around week 60 on the medication.
March 8, 2024: The FDA approved Wegovy to reduce the risk of cardiovascular events and stroke in people who have cardiovascular disease long with overweight or obesity. In the study, 8% of people who took a placebo had a cardiovascular event compared to 6.5% of those who took Wegovy. While weight loss achieved through diet and exercise also lowers risk of heart attacks and strokes, the drug’s manufacturer claims that the benefits with Wegovy are greater than those from weight loss alone. The mechanisms are not yet clear, but the company says that trial participants experienced the benefits even before they started losing weight. Still, 16.6% of patients taking Wegovy dropped out of the trial due to adverse events (compared to 8.2% of those in the placebo group).
December 14, 2023: Novo Nordisk published results of a large trial (including over 17,000 participants) testing Wegovy on patients with excess weight and diagnosed heart disease, but who did not have diabetes. They found that the drug lowered the risk of cardiovascular events such as heart attacks, stroke, and deaths over the course of about five years. It’s important to note that the trial did not specify lifestyle changes such as diet or exercise for participants who took Wegovy or who took a placebo.
August 18, 2023: A study shows that real-world weight loss (outside of clinical trials) is less dramatic than what was seen in the clinical trials with semaglutide. With real world use, patients lost an average of 4.4% of their body weight over the course of one year. In the initial trials, 60% of patients lost 10% or more of their body weight during that time frame.
May 25, 2023: Researchers begin Phase 3 trials to see if semaglutide can help people with early Alzheimer’s disease.
April 19, 2022: Patients gain back two-thirds of the weight they lost within one year of stopping semaglutide, according to a study.
Drug Approval Timeline
Drugs that act like GLP-1 (glucagon-like peptide-1) have been used to treat diabetes since 2005. As patients and doctors started to notice unintentional weight loss that accompanied use of the drugs, scientists started testing these types of drugs for that explicit purpose, rather than just for diabetes treatment.
March 8, 2024: The FDA approved Wegovy to reduce the risk of cardiovascular events and stroke in people who have overweight or obesity along with cardiovascular disease.
November 8, 2023: The FDA approved Zepbound, (tirzepatide), which uses the same mechanism as semaglutide to treat obesity. Zepbound is the same drug, with the same dose, as Mounjaro. The only difference is that Zepbound is approved for weight loss while Mounjaro is approved for diabetes. Using two different names for the same drug is purely a marketing choice in this scenario.
May 13, 2023: The FDA Approved Mounjaro (tirzepatide) to treat type 2 diabetes using a similar mechanism as semaglutide.
June 4, 2021: The FDA approved Wegovy, a higher dose of semaglutide than Ozempic, to treat obesity.
December 2017: The FDA approved Ozempic, a form of semaglutide to treat type 2 diabetes.
