Ozempic Side Effects: Rare but Serious Adverse Events Explained

Which serious side effects does the Ozempic label list?

The Ozempic label effective June 2026 carries one boxed warning and a set of warnings and precautions: thyroid C-cell tumors, acute pancreatitis, diabetic retinopathy complications, hypoglycemia when combined with insulin or an insulin secretagogue, acute kidney injury from volume depletion, severe gastrointestinal reactions, hypersensitivity reactions, acute gallbladder disease, and pulmonary aspiration during general anesthesia or deep sedation [1]. The label also says the pen must never be shared between patients, even with a new needle, because of the risk of transmitting blood-borne pathogens [1].

The label also reports common gastrointestinal effects, including nausea, diarrhea and vomiting [1]. In the pooled placebo-controlled trials behind the label — 262 patients on placebo, 260 on 0.5 mg and 261 on 1 mg, mean exposure 32.9 weeks — nausea occurred in 15.8% and 20.3% versus 6.1% on placebo, diarrhea in 8.5% and 8.8% versus 1.9%, and vomiting in 5% and 9.2% versus 2.3% [1]. Any gastrointestinal reaction was reported in 32.7% and 36.4% versus 15.3%, and 3.1% and 3.8% stopped treatment for a gastrointestinal reason versus 0.4% on placebo [1]. Severe gastrointestinal reactions were much less frequent: 0.4% on 0.5 mg and 0.8% on 1 mg versus 0% on placebo [1].

Several of the label's rarer entries are postmarketing reports, and the label notes that a frequency cannot be estimated from voluntary reports [1]. Hair loss and dysesthesia, an altered skin sensation such as burning or pain from touch, are among those reports [1].

Thyroid C-cell tumors: the boxed warning

In mice and rats, semaglutide caused dose-dependent and treatment-duration-dependent thyroid C-cell tumors (adenomas and carcinomas) after lifetime exposure at clinically relevant plasma exposures [1]. The label states that it is unknown whether Ozempic causes thyroid C-cell tumors, including medullary thyroid carcinoma (MTC), in humans, because the human relevance of the rodent finding has not been determined [1]. MTC has been reported in the postmarketing period with liraglutide, another GLP-1 receptor agonist, but the label says those reports are insufficient to establish or exclude a causal relationship [1].

Ozempic is contraindicated in people with a personal or family history of MTC or with MEN 2 [1]. The label directs prescribers to counsel patients about the symptoms of thyroid tumors: a mass in the neck, difficulty swallowing, shortness of breath, persistent hoarseness [1]. It also says routine serum calcitonin monitoring or thyroid ultrasound is of uncertain value for early detection, that such monitoring may lead to unnecessary procedures given the low specificity of calcitonin and the high background rate of thyroid disease, and that a significantly elevated calcitonin value (patients with MTC usually have values above 50 ng/L) or thyroid nodules found on examination or imaging need further evaluation [1].

Acute pancreatitis

The label reports acute pancreatitis, including fatal and nonfatal hemorrhagic or necrotizing pancreatitis, in patients treated with GLP-1 receptor agonists including Ozempic [1]. The signs the label names are persistent or severe abdominal pain, sometimes radiating to the back, which may or may not be accompanied by nausea or vomiting; if pancreatitis is suspected, the label says to discontinue Ozempic and begin appropriate management [1]. Acute and necrotizing pancreatitis, sometimes fatal, also appear among the label's postmarketing reports [1].

Diabetic retinopathy complications

In a 2-year trial of adults with type 2 diabetes and high cardiovascular risk, diabetic retinopathy complications occurred in 3.0% of patients on Ozempic versus 1.8% on placebo [1]. The gap was wider in people who already had retinopathy at baseline (8.2% versus 5.2%) than in those with no known history (0.7% versus 0.4%) [1].

The label notes that rapid improvement in glucose control has been associated with temporary worsening of diabetic retinopathy, and that the effect of long-term glycemic control on these complications has not been studied [1]. It says patients with a history of diabetic retinopathy should be monitored for progression [1].

Severe GI reactions, ileus and gastroparesis

Ozempic is not recommended in patients with severe gastroparesis, a statement that sits inside the severe gastrointestinal reactions warning [1]. The label does not say that semaglutide causes gastroparesis. It does say that semaglutide delays gastric emptying, which is also the reason it can affect the absorption of other oral drugs [1]. Postmarketing reports listed in the label include ileus, intestinal obstruction and severe constipation with fecal impaction [1].

Acute kidney injury

The label describes postmarketing reports of acute kidney injury, in some cases requiring hemodialysis, mostly in patients who had gastrointestinal reactions such as nausea, vomiting or diarrhea leading to dehydration [1]. It says to monitor renal function in patients reporting reactions that could lead to volume depletion, especially during dose initiation and escalation [1]. No dose adjustment is recommended for renal impairment, and no clinically relevant change in semaglutide exposure was seen in people with renal impairment including kidney failure [1].

Ozempic also carries a kidney outcomes indication. In FLOW, 3,533 adults with type 2 diabetes and chronic kidney disease were assigned to semaglutide 1 mg weekly or placebo and followed for a median of 3.4 years, and the composite of kidney failure, a 50% or greater eGFR decline, or kidney or cardiovascular death occurred in 18.7% versus 23.2% (HR 0.76, 95% CI 0.66 to 0.88) [3]. That long-term result is a separate matter from the short-term dehydration risk.

Gallbladder disease

Acute gallbladder disease is a label warning: if cholelithiasis or cholecystitis is suspected, gallbladder studies are indicated [1]. Cholecystitis and cholecystectomy appear among the postmarketing reports in the label [1].

Hypoglycemia with insulin or sulfonylureas

Ozempic stimulates insulin release in the presence of elevated blood glucose, and in the monotherapy trial documented symptomatic hypoglycemia at or below 70 mg/dL occurred in 0% on placebo, 1.6% on 0.5 mg and 3.8% on 1 mg, with no severe events [1]. When Ozempic is combined with an insulin secretagogue such as a sulfonylurea, or with insulin, the risk of hypoglycemia including severe hypoglycemia rises, and the label says reducing the dose of the sulfonylurea or insulin may be necessary when Ozempic is started [1]. In the label's 30-week trial of Ozempic added to basal insulin with or without metformin, documented symptomatic hypoglycemia at or below 70 mg/dL occurred in 15.2% on placebo, 16.7% on 0.5 mg and 29.8% on 1 mg, and severe hypoglycemia requiring another person's assistance in 0%, 0% and 1.5% [1]. When Ozempic is used with insulin, the label instructs separate injections that are never mixed, which may go in the same body region but not at adjacent sites [1].

Vision loss from NAION: a European finding

EMA's safety committee concluded in June 2025 that non-arteritic anterior ischemic optic neuropathy (NAION) is a very rare side effect of semaglutide, meaning it may affect up to 1 in 10,000 people [2]. Large epidemiological studies in adults with type 2 diabetes suggested an approximately two-fold increase in risk, corresponding to about one additional case per 10,000 person-years of treatment [2]. EMA recommended updating the product information to include NAION at a frequency of very rare, and that semaglutide be stopped if NAION is confirmed [2]. The current US Ozempic label does not name NAION or optic neuropathy; its vision-related advice concerns monitoring for diabetic retinopathy [1].

Suicidal thoughts

The current Ozempic label carries no warning about suicidal behavior or ideation, and neither does the label for Rybelsus and Ozempic tablets [1][4].

Hypersensitivity and pulmonary aspiration

Anaphylaxis and angioedema have been reported with Ozempic, and a prior serious hypersensitivity reaction to semaglutide or to an excipient is a contraindication [1]. The label says to discontinue Ozempic if a hypersensitivity reaction occurs, treat promptly per standard of care, and monitor until signs and symptoms resolve [1]. Pulmonary aspiration during general anesthesia or deep sedation has been reported in patients receiving GLP-1 receptor agonists, and the label instructs patients to inform healthcare providers of any planned surgeries or procedures [1].