Wegovy Side Effects: Rare but Serious Adverse Events You Need to Know

What does the thyroid C-cell tumor boxed warning actually say?

In mice and rats, semaglutide caused a dose-dependent and treatment-duration-dependent increase in thyroid C-cell tumors (adenomas and carcinomas) at clinically relevant plasma exposures [1]. Whether it causes thyroid C-cell tumors, including medullary thyroid carcinoma (MTC), in humans is unknown, because the human relevance of the rodent findings has not been determined [1].

Wegovy is contraindicated in people with a personal or family history of MTC or with Multiple Endocrine Neoplasia syndrome type 2 (MEN 2) [1]. The label says to counsel patients on the symptoms of thyroid tumors: a mass in the neck, trouble swallowing, shortness of breath and persistent hoarseness [1].

Routine serum calcitonin monitoring or thyroid ultrasound is of uncertain value for early detection, and the label notes such monitoring may lead to unnecessary procedures given the low specificity of calcitonin and the high background rate of thyroid disease [1]. The label says a significantly elevated serum calcitonin value may indicate MTC, that patients with MTC usually have calcitonin values greater than 50 ng/L, and that an elevated value and thyroid nodules found on examination or neck imaging should be further evaluated [1]. Postmarketing reports of MTC exist for liraglutide, another GLP-1 receptor agonist, but the label says those reports are insufficient to establish or exclude a causal relationship with GLP-1 receptor agonists in humans [1].

How often does pancreatitis happen on Wegovy?

Acute pancreatitis, including fatal and non-fatal hemorrhagic or necrotizing pancreatitis, has been observed in patients treated with GLP-1 receptor agonists, including Wegovy [1]. In the Wegovy weight-management trials, acute pancreatitis was confirmed in 4 semaglutide-treated adults (0.2 per 100 patient-years) versus 1 on placebo [1].

The label describes the presentation as persistent or severe abdominal pain, sometimes radiating to the back, which may or may not be accompanied by nausea or vomiting, and says to discontinue Wegovy and start appropriate management if pancreatitis is suspected [1]. Separately, average amylase rose 15% to 16% and lipase rose 39% in the trials; the label states the significance of these enzyme changes is unknown in the absence of pancreatitis symptoms [1].

Gallbladder disease

Gallbladder disease is one of Wegovy's serious risks. In adult injection trials, gallstones occurred in 1.6% of Wegovy-treated patients versus 0.7% on placebo, and cholecystitis in 0.6% versus 0.2% [1]. With the 25 mg Wegovy tablets, cholelithiasis was 2.5% versus 1% on placebo, and in the pediatric injection trial it was 3.8% versus 0% (cholecystitis 0.8% versus 0%) [1].

The label notes that substantial or rapid weight loss can raise gallstone risk, but that acute gallbladder disease was more common on Wegovy than placebo even after accounting for the degree of weight loss [1]. If cholelithiasis is suspected, the label calls for gallbladder studies and clinical follow-up [1].

Acute kidney injury from dehydration

The label's warning is specific: acute kidney injury due to volume depletion, with renal function monitoring advised in patients reporting reactions that could lead to volume depletion [1]. In the Wegovy program, acute kidney injury occurred at 0.4 versus 0.2 cases per 100 patient-years (7 versus 4 adults), more often in patients with prior renal impairment and during dose titration, and often after gastrointestinal fluid loss [1].

Heart rate increase

The Wegovy label reports a mean resting heart rate increase of 1 to 4 beats per minute, and a rise of 20 bpm or more in 26% of semaglutide-treated patients versus 16% on placebo [1]. The label says to monitor heart rate at regular intervals [1].

Hypersensitivity and injection-site reactions

Anaphylaxis and angioedema have been reported with semaglutide, and a prior serious hypersensitivity reaction to semaglutide or any excipient is a contraindication [1]. The label says to discontinue Wegovy if a hypersensitivity reaction is suspected [1]. Injection-site reactions were reported by 1.4% of semaglutide-treated patients versus 1% on placebo [1].

Diabetic retinopathy complications

This signal comes from the diabetes trials, not the weight-management ones. In SUSTAIN-6, a 104-week trial of 3,297 adults with type 2 diabetes given subcutaneous semaglutide 0.5 or 1 mg weekly or placebo, diabetic retinopathy complications occurred in 3.0% on semaglutide versus 1.8% on placebo [1][3], a hazard ratio of 1.76 (95% CI 1.11 to 2.78) [5]. The absolute difference was larger in patients who already had retinopathy at baseline: 8.2% versus 5.2% [1][3]. The label notes that rapid improvement in glucose control has been associated with temporary worsening of retinopathy, and says patients with a history of diabetic retinopathy should be monitored for progression [1].

Pulmonary aspiration during anesthesia or sedation

The label says pulmonary aspiration has been reported in patients receiving GLP-1 receptor agonists undergoing elective surgeries or procedures, and that patients should be instructed to inform healthcare providers of any planned surgeries or procedures [1].

Severe GI reactions, ileus and gastroparesis

Severe gastrointestinal adverse reactions were reported by 4.1% of semaglutide-treated patients versus 0.9% on placebo in the adult injection trials [1]. Postmarketing reports in the Ozempic and Wegovy labels include ileus, intestinal obstruction, and severe constipation including fecal impaction [1]. On gastroparesis, the label says only that Wegovy is not recommended in patients with severe gastroparesis; it does not state that semaglutide causes gastroparesis [1]. Overall, 6.8% of patients on Wegovy 2.4 mg stopped treatment because of adverse reactions, versus 3.2% on placebo [1].

NAION: the eye condition Europe lists and the US label does not

In June 2025, EMA's safety committee concluded that non-arteritic anterior ischemic optic neuropathy (NAION) is a very rare side effect of semaglutide medicines, affecting up to 1 in 10,000 people [2]. Large epidemiological studies in adults with type 2 diabetes suggested roughly a two-fold relative risk, corresponding to about one additional case per 10,000 person-years of treatment, and the committee recommended updating product information and stopping semaglutide if NAION is confirmed [2]. The current US Wegovy warnings section does not mention NAION or optic neuropathy [1].

The suicidality warning

The suicidal behavior and ideation warning was removed from the Wegovy label in February 2026, and the current Wegovy label contains no such warning [1].

Hypoglycemia with insulin or sulfonylureas

In adults with type 2 diabetes and a BMI of 27 or higher, glucose below 54 mg/dL occurred in 6.2% on Wegovy 2.4 mg versus 2.5% on placebo, with higher risk in people taking a sulfonylurea; adding Wegovy to insulin has not been evaluated [1]. The label says reducing the dose of the insulin or insulin secretagogue may be necessary when starting Wegovy [1].

What FDA adverse event reports can show

Reports in the FDA adverse event system are voluntary and cannot be used to estimate how often an event occurs or to establish that a drug caused it [6].