Semaglutide Side Effects: Rates From the FDA Labels

Semaglutide is sold under different brand names studied in different populations, so there is no single incidence table. Ozempic's runs from two placebo-controlled trials in type 2 diabetes, 521 patients on drug, mean exposure 32.9 weeks:

Wegovy's table comes from three placebo-controlled obesity trials, 2,116 adults on 2.4 mg for up to 68 weeks, and it is roughly two to three times higher on every gastrointestinal line:

Hair loss surprises people. The Wegovy label attributes it to the weight reduction rather than to semaglutide directly, and the sex split makes that plausible: in the pooled 2.4 mg trials it was reported by 4% of women and 0.9% of men.

Same molecule, very different tables. Three things drive the gap. The maintenance dose is higher for weight management (2.4 mg versus 0.5 to 2 mg). The populations differ — people with type 2 diabetes on Ozempic, largely people without diabetes on Wegovy. And the reporting thresholds differ: Ozempic's table lists reactions occurring in at least 5% of treated patients, Wegovy's lists anything at 2% or above, so Wegovy's simply has more rows by construction.

If you are comparing molecules rather than brands, our tirzepatide vs semaglutide comparison and the GLP-1 medications overview line the classes up side by side.

Wegovy now has an approved maintenance dose above 2.4 mg. In two 72-week trials including 1,311 patients on 7.2 mg once weekly, nausea reached 39% (versus 35% on 2.4 mg and 13% on placebo) and vomiting 22%.

The genuinely new signal at that dose is dysesthesia — altered skin sensation, covering paresthesia, burning sensation, hyperesthesia, allodynia and sensitive skin. It was reported by 22% of patients on 7.2 mg, 6% on 2.4 mg, and 0.3% on placebo. The label states the incidence rose with dosage and with drug levels in the blood. Among the 288 patients who experienced it on 7.2 mg, 2% stopped permanently, 8% interrupted treatment and 23% had a dose reduction; 18% did not report recovering during the trial, and of 38 patients who recovered and were then re-escalated to 7.2 mg, 17 (45%) had it come back.

• Thyroid C-cell tumors (boxed warning). Semaglutide caused dose-dependent thyroid C-cell tumors in mice and rats at clinically relevant exposures. Whether it does so in humans is unknown. It is contraindicated with a personal or family history of medullary thyroid carcinoma or MEN 2.
• Acute pancreatitis. In the adult weight-reduction trials, adjudicated acute pancreatitis occurred in 4 Wegovy patients (0.2 cases per 100 patient-years) versus 1 on placebo. Necrotizing pancreatitis, sometimes fatal, appears in the postmarketing section.
• Gallbladder disease. Cholelithiasis in 1.6% of injection-treated adults versus 0.7% on placebo; cholecystitis 0.6% versus 0.2%. The label notes the excess persists even after accounting for how much weight was lost.
• Acute kidney injury. 7 cases versus 4 on placebo in the weight trials, mostly alongside vomiting, diarrhea or dehydration, and more often during titration.
• Severe gastrointestinal reactions. Reported in 4.1% of Wegovy injection patients versus 0.9% on placebo. Wegovy is not recommended in patients with severe gastroparesis. Ileus, intestinal obstruction and fecal impaction appear in postmarketing reports.
• Heart rate increase. Mean resting increases of 1 to 4 bpm, but 26% of treated adults hit a maximum change of 20 bpm or more at some visit, versus 16% on placebo.
• Pulmonary aspiration under anesthesia. Rare postmarketing reports in patients with retained gastric contents despite fasting. The label says available data are insufficient to recommend a mitigation strategy, and to tell your care team before any procedure.
• Less-discussed signals. Appendicitis in 0.5% versus 0.2%; hip and pelvis fractures in 1% of women on Wegovy versus 0.2% on placebo in the cardiovascular outcomes trial; urolithiasis 1.2% versus 0.8%; mean lipase elevation of 39% from baseline, of unknown significance without symptoms.

An independent cohort study in JAMA compared GLP-1 users to bupropion-naltrexone users and found higher adjusted risks of pancreatitis (HR 9.09), bowel obstruction (HR 4.22) and gastroparesis (HR 3.67), but not biliary disease. Read those confidence intervals before quoting the numbers — pancreatitis was 1.25 to 66.00, on two events among 613 semaglutide users, and the analysis pooled semaglutide with liraglutide. It supports "these are real and rare," not a precise risk figure.

A 2024 Massachusetts Eye and Ear cohort found a higher rate of non-arteritic anterior ischemic optic neuropathy (NAION) in patients prescribed semaglutide — HR 4.28 in type 2 diabetes and 7.64 in the overweight or obese group. But that registry contained only patients already referred to neuro-ophthalmologists, so its 8.9% cumulative incidence is not a population rate.

A larger 2025 study across 160 healthcare organizations in 21 countries, covering roughly 297,000 matched participants, found no significant association at one, two or three years in any subgroup.

The honest summary: two well-conducted studies disagree, the effect size in the general population is unresolved, and NAION does not appear in the current US Ozempic or Wegovy labels. What those labels do carry is a warning about diabetic retinopathy complications in patients with type 2 diabetes — 3% versus 1.8% in a two-year cardiovascular trial, concentrated in patients who already had retinopathy at baseline.

This is the part most side-effect articles skip, and it is the one this site exists for.

FDA has issued an alert about dosing errors with compounded injectable semaglutide, including adverse events requiring hospitalization. The reported magnitude is not subtle: patients administered five to 20 times the intended dose. The mechanism was almost always a vial and a syringe rather than a pen.

The specific failure FDA describes: patients told to draw "5 units" (0.05 mL) on a U-100 insulin syringe drew 50 units instead. Providers converting milligrams to units miscalculated — one prescribed 25 units meaning 0.25 mg (5 units), causing severe vomiting; another prescribed 20 units instead of 2, affecting three patients. Compounded products come in concentrations that vary by compounder, and instructions are often written in "units," a volume that means nothing without knowing the concentration.

Because semaglutide's half-life is about a week, the label notes that a prolonged period of observation and treatment may be necessary after an overdose. There is no way to take back a tenfold error.

If you are working from a vial rather than a pen, the arithmetic is the safety step. Our syringe measurement guide covers reading U-100 markings without confusing units for millilitres, the reconstitution guide covers concentration maths, and the semaglutide calculator shows the volume for a given concentration and target dose. Actual dose selection is a prescriber's decision, not something to derive from a chart.