The worst side effects of Wegovy range from persistent nausea that forces some people to stop treatment entirely, to rare but serious complications like pancreatitis, gallstones, and kidney injury. Most side effects are gastrointestinal and manageable, but roughly 4.3% of patients in clinical trials had to quit Wegovy because of gut-related problems, compared to just 0.7% on placebo. Beyond the common discomfort, Wegovy carries an FDA black box warning for a potential thyroid tumor risk, the most serious safety label a drug can receive.
Gastrointestinal Problems Are the Most Common
Nausea is the single biggest reason people stop taking Wegovy. In clinical trials, 1.8% of patients discontinued specifically because of nausea, and another 1.2% quit because of vomiting. Diarrhea drove an additional 0.7% to stop. These numbers may sound small, but they represent the people who couldn’t tolerate the drug at all. A much larger share of patients experienced these symptoms but pushed through them.
Wegovy works partly by slowing how fast your stomach empties, which is why you feel full longer. The flip side is that food sitting in your stomach longer can trigger nausea, bloating, and acid reflux, especially early in treatment. The drug uses a gradual dose increase over several months, starting at 0.25 mg per week and stepping up every four weeks, specifically to give your body time to adjust. Some people need to stay at a lower dose longer than the standard four weeks before moving up.
Stomach Paralysis (Gastroparesis)
A more severe version of that slowed digestion is gastroparesis, where the stomach essentially stops moving food along normally. A large study of about 16 million U.S. patient records found that people taking GLP-1 drugs like Wegovy had 3.67 times the risk of gastroparesis compared to people taking a different weight-loss medication. Symptoms include persistent vomiting, nausea, and abdominal pain that goes beyond the typical adjustment period. Researchers note that while gastroparesis remains rare on an individual level, the sheer number of people now using these drugs means it could affect hundreds of thousands of people worldwide.
Gallstones and Gallbladder Disease
Wegovy roughly doubles your risk of developing gallstones. In a meta-analysis of clinical trials, 2.3% of semaglutide patients developed gallstones compared to 0.9% on placebo, a 159% increase in risk. This isn’t unique to the drug itself. Rapid weight loss from any cause, including surgery or strict dieting, is a well-known trigger for gallstone formation. When you lose fat quickly, your liver releases more cholesterol into bile, which can crystallize into stones.
Gallstones don’t always cause symptoms, but when they do, you’ll typically feel sharp pain in the upper right side of your abdomen, sometimes with fever, yellowing of the skin or eyes, or clay-colored stools. Some cases require surgery to remove the gallbladder.
Thyroid Tumor Warning
Wegovy’s prescribing label carries an FDA black box warning because semaglutide caused thyroid C-cell tumors in rodents at doses similar to what humans take. Whether this translates to a real cancer risk in people is still unknown. Because of this uncertainty, Wegovy is completely off-limits if you have a personal or family history of medullary thyroid carcinoma or a condition called Multiple Endocrine Neoplasia syndrome type 2.
Signs to watch for include a lump or swelling in your neck, persistent hoarseness, difficulty swallowing, or shortness of breath. There’s no reliable screening test for early detection in people taking the drug. Routine thyroid ultrasounds and blood tests for calcitonin haven’t been shown to catch problems early enough to be useful in this context.
Pancreatitis
Acute pancreatitis, inflammation of the pancreas, is one of the more dangerous potential complications. It causes severe abdominal pain that comes on quickly, often radiating to the back, along with nausea, vomiting, and fever. Data from the UK’s medicines regulator shows 1,296 reports of pancreatitis, including 19 deaths, among people taking GLP-1 drugs between 2007 and October 2025. That spans multiple drugs in the class over nearly two decades and millions of users, so the absolute risk is low, but the consequences can be severe.
If you develop sudden, intense stomach pain that doesn’t let up, that’s a reason to stop taking Wegovy and seek medical attention immediately. Pancreatitis can become life-threatening if untreated.
Kidney Injury
Wegovy doesn’t appear to damage the kidneys directly, but it can set the stage for kidney problems through an indirect route. Severe nausea and vomiting lead to dehydration, and dehydration is a well-established cause of acute kidney injury. The drug may compound this by increasing how much sodium your kidneys excrete, which further disrupts fluid balance. Most reported cases of kidney injury in people on GLP-1 drugs trace back to significant dehydration from gastrointestinal side effects, especially in people already taking blood pressure medications that affect kidney function.
Staying well-hydrated matters more on Wegovy than it normally would. If you’re vomiting frequently or unable to keep fluids down for an extended period, that’s a situation that needs medical attention before it spirals into kidney trouble.
Heart Rate Changes
Wegovy can raise your resting heart rate. The FDA label instructs patients to pay attention to a racing or pounding heartbeat while at rest, particularly if it lasts several minutes. A sustained increase in resting heart rate is a reason to discontinue the drug. This isn’t the temporary spike you’d feel after exercise or caffeine. It’s a persistent elevation that you notice while sitting still.
Suicidal Thoughts: What the Evidence Shows
Early concerns about a possible link between GLP-1 drugs and suicidal thoughts prompted an extensive FDA investigation. The agency analyzed 91 placebo-controlled trials covering nearly 108,000 patients and found no increased risk of suicidal ideation, self-harm, depression, anxiety, or psychosis. A separate real-world study of over 2.2 million patients reached the same conclusion. Based on this evidence, the FDA has requested that manufacturers remove the suicidal behavior warning from Wegovy’s label entirely. The investigation found no causal relationship between GLP-1 drugs and suicidal thoughts.
Severe Allergic Reactions
Anaphylaxis and angioedema (severe swelling of the face, lips, tongue, or throat) have been reported with Wegovy, though they are rare. Symptoms include rapid heartbeat, difficulty breathing or swallowing, severe rash, and dizziness or fainting. Anyone who has had a serious allergic reaction to semaglutide should not use the drug again. These reactions can happen with any injectable medication and require emergency treatment.