Semaglutide Side Effects: What Wegovy and Ozempic Report

Most articles about semaglutide side effects quote one set of numbers. That is the first mistake, because semaglutide has two current FDA labels — Wegovy, approved for weight reduction, and Ozempic, approved for type 2 diabetes — and they do not describe the same drug's safety profile. Same molecule, same manufacturer, different dose, different population, and, as it turns out, meaningfully different numbers. This article reads both labels section by section, says which population each figure describes, and states plainly where the two disagree.

The boxed warning both labels carry

Both Wegovy and Ozempic open with the same boxed warning, and its wording matters more than its headline. In rodents, semaglutide caused "a dose-dependent and treatment-duration-dependent increase in the incidence of thyroid C-cell tumors (adenomas and carcinomas) after lifetime exposure at clinically relevant plasma exposures¹." What the labels then say about humans is the part usually dropped: "It is unknown whether WEGOVY causes thyroid C-cell tumors, including MTC, in humans, as human relevance of semaglutide-induced rodent thyroid C-cell tumors has not been determined¹." Ozempic's §5.1 says the identical thing about Ozempic².

Both labels are contraindicated in patients with a personal or family history of medullary thyroid carcinoma or with Multiple Endocrine Neoplasia syndrome type 2. Both also state that routine monitoring by serum calcitonin or thyroid ultrasound "is of uncertain value for early detection of MTC" and "may increase the risk of unnecessary procedures¹²" — a warning against over-screening sitting inside a warning about tumors, which is not how a vendor page ever summarizes it.

Eleven numbered warnings on one label, ten on the other

Wegovy's §5 runs to eleven numbered subsections; Ozempic's runs to ten, and the two lists are not the same ten. Read side by side:

Both labels carry: thyroid C-cell tumor risk (5.1 on both), acute pancreatitis (5.2 on both), acute kidney injury due to volume depletion, severe gastrointestinal adverse reactions, hypersensitivity reactions, acute gallbladder disease, pulmonary aspiration during general anesthesia or deep sedation, and a pen-sharing warning¹².

Wegovy carries and Ozempic does not: a general hypoglycemia warning (§5.4) that opens "WEGOVY lowers blood glucose and can cause hypoglycemia" — Ozempic's equivalent (§5.5) is narrower by title, covering hypoglycemia only "with Concomitant Use of Insulin Secretagogues or Insulin." And §5.9, Heart Rate Increase, which has no numbered counterpart on Ozempic's label at all, even though Ozempic's own §6.1 reports "a mean increase in heart rate of 2 to 3 beats per minute" against a mean decrease of 0.3 bpm on placebo². The same physiological effect is a numbered warning on one label and a §6.1 observation on the other.

On the gastrointestinal warning, the two labels report different drugs. Wegovy's §5.6 states that severe gastrointestinal adverse reactions "were reported in 4.1% and 0.9% of WEGOVY injection and placebo-treated patients, respectively¹." Ozempic's §5.7 states that in its own trials, severe gastrointestinal reactions occurred in "0.5 mg 0.4%, 1 mg 0.8%" of patients versus "0%" on placebo². Both labels also say the drug "is not recommended in patients with severe gastroparesis."

The adult adverse-reaction table, as published

That is Wegovy's own Table 3, from §6.1: adults with obesity or overweight, 2,116 of them on 2.4 mg weekly injection for up to 68 weeks, against 1,261 on placebo¹. One detail worth flagging, because it shows what reading the label rather than a summary of it gets you: the narrative paragraph directly beneath that table cites vomiting at "25% vs. 6%" while the table itself lists 24%, because the narrative pools a slightly different set of trials. The difference is trivial; the fact that a label can be internally inconsistent by a point is worth knowing before you treat any single figure as exact.

The discontinuation numbers give a better sense of tolerability than any single symptom rate. In those adult trials, 6.8% of patients on Wegovy and 3.2% on placebo permanently stopped treatment because of an adverse reaction, with nausea (1.8% vs. 0.2%), vomiting (1.2% vs. 0%) and diarrhea (0.7% vs. 0.1%) the leading causes¹. Overall, 73% of Wegovy-treated adults reported some gastrointestinal reaction against 47% on placebo — the reactions are close to universal at a mild level and rarely severe enough to stop treatment.

The pediatric table is a different table, and gets quoted as if it weren't

Wegovy's §6.1 contains three adverse-reaction tables, not one. Table 3 is adults on 2.4 mg. Table 4 is the 7.2 mg dosage. Table 5 is pediatric patients aged 12 and older — 133 on Wegovy against 67 on placebo — and its numbers are not the adult numbers. Vomiting is 36% in the pediatric table against 24% in the adult one. Cholelithiasis, per §5.3, was "reported by 3.8% of WEGOVY injection-treated patients and 0% placebo-treated patients" in the pediatric trial against 1.6% versus 0.7% in the adult trials — the label states outright that "the incidence of cholelithiasis and cholecystitis was higher in WEGOVY injection-treated pediatric patients aged 12 years and older than in WEGOVY injection-treated adults¹." Heart rate diverges the same way: 54% of pediatric patients versus 39% on placebo had a maximum increase of 20 bpm or more, against 26% versus 16% in adults.

The 7.2 mg table adds a symptom that barely registers at lower doses. Dysesthesia — altered skin sensation, including paresthesia, burning and skin pain — was reported in 22% of patients on 7.2 mg, 6% on 2.4 mg, and 0.3% on placebo, and the label states directly that "the incidence of dysesthesia with WEGOVY increased with increasing dosage and drug levels in the blood¹." Among the 288 patients who experienced it on 7.2 mg, 18% "did not report recovering during the trial duration."

Same molecule, two labels, different numbers

That table is the tension this article exists to state rather than resolve. There are three real reasons those columns diverge, and none of them is that one label is wrong.

Dose. Ozempic's approved maximum for type 2 diabetes is 2 mg weekly and its placebo-controlled adverse-reaction pool runs at 0.5 mg and 1 mg; Wegovy's pivotal weight-reduction pool runs at 2.4 mg, with a 7.2 mg dosage now on the same label. Semaglutide's gastrointestinal effects are dose-dependent, and the label's own dysesthesia section says so explicitly for at least one of them.

Population. Ozempic's Table 1 pool is 521 patients with type 2 diabetes, mean age 56, on metformin or basal insulin, followed a mean of 32.9 weeks. Wegovy's Table 3 pool is 2,116 adults with obesity or overweight, mean age 48, 71% female, only 19% of whom had type 2 diabetes, followed up to 68 weeks. Those populations differ in age, sex balance, baseline glycemia and duration of exposure.

What each program was designed to capture. Ozempic's Table 1 reports reactions occurring in at least 5% of treated patients; Wegovy's Table 3 uses a 2% threshold, and its pediatric table uses 3%. A lower reporting floor surfaces more rows. Wegovy's program also ran a dedicated cardiovascular outcomes trial in which "safety data collection was limited to serious adverse events..., adverse events leading to discontinuation, and adverse events of special interest¹" — a deliberately narrowed capture that produces different denominators again.

Where the trial publications and the labels part company

The pivotal weight-reduction trial behind Wegovy, STEP 1, was published in the New England Journal of Medicine and its own abstract summarizes tolerability this way: "Nausea and diarrhea were the most common adverse events with semaglutide; they were typically transient and mild-to-moderate in severity and subsided with time³." It reports that "more participants in the semaglutide group than in the placebo group discontinued treatment owing to gastrointestinal events (59 [4.5%] vs. 5 [0.8%])."

Read that alone and semaglutide looks gently tolerated. The label built from the same program reports that 73% of adults had a gastrointestinal reaction and 4.1% had a severe one¹. Both statements are accurate, and the reason they coexist is that "transient and mild-to-moderate" describes the typical case while "4.1% severe" describes the tail — a summary sentence about the median patient and a required disclosure about the minority are answering different questions. This site's position is that a reader deciding whether to start the drug needs both, and that quoting only the trial's reassuring sentence is the more common error.

The clearest example of a trial finding surviving into a label as a hard warning is retinopathy. SUSTAIN-6, the cardiovascular outcomes trial in 3,297 patients with type 2 diabetes, reported that "rates of new or worsening nephropathy were lower in the semaglutide group, but rates of retinopathy complications (vitreous hemorrhage, blindness, or conditions requiring treatment with an intravitreal agent or photocoagulation) were significantly higher (hazard ratio, 1.76; 95% CI, 1.11 to 2.78; P=0.02)⁴" — inside a trial whose headline result was a 26% reduction in major cardiovascular events. Both labels carry that finding forward: Wegovy as §5.8, titled specifically "Diabetic Retinopathy Complications in Patients with Type 2 Diabetes," and Ozempic as §5.3, both reporting 3% versus 1.8% and both noting the absolute risk increase was concentrated in patients who already had retinopathy at baseline (8.2% vs. 5.2%) rather than in those who did not (0.7% vs. 0.4%)¹².

The findings that do not fit the gastrointestinal story

Three label findings get almost no coverage and are worth naming because they are not stomach complaints.

Fractures. In Wegovy's cardiovascular outcomes trial, "more fractures of the hip and pelvis were reported on WEGOVY than on placebo in female patients: 1% (24/2,448) vs. 0.2% (5/2,424), and in patients ages 75 years and older: 2.4% (17/703) vs. 0.6% (4/663)¹." Those are small absolute numbers in a very large trial, and the label reports them without asserting a mechanism.

Hair loss. Wegovy's Table 3 lists it at 3% versus 1%, and the narrative section breaks it out by sex and dose: 3.3% on 2.4 mg (4% of women, 0.9% of men) against 1% on placebo, rising to 5.8% on 7.2 mg (8.4% of women, 0.2% of men). The label states that hair loss reactions "were associated with weight reduction¹" rather than attributing them to the drug directly — a distinction our article on whether Ozempic causes hair loss works through in full, because the mechanism (telogen effluvium following rapid weight loss) is genuinely different from the gastrointestinal reactions.

Pulmonary aspiration. Both labels added a numbered warning about residual gastric contents during general anesthesia or deep sedation, and both are unusually candid that nobody knows what to do about it: "Available data are insufficient to inform recommendations to mitigate the risk of pulmonary aspiration... including whether modifying preoperative fasting recommendations or temporarily discontinuing [the drug] could reduce the incidence of retained gastric contents¹²." The label's only instruction is to tell your surgical team you are on it.

What none of this describes

Every figure above comes from an FDA-approved, brand-manufactured semaglutide product administered in a controlled trial at a dose the label specifies — our page on what those label dosages actually are covers the escalation schedules in full. It does not describe a compounded semaglutide vial, which is not FDA-reviewed for identity, concentration or purity and may not contain what the label describes at all; our explainer on compounded semaglutide covers what that legally is and is not. Nor do these tables describe the oral tablet formulations, which have their own separate figures — our article on the Wegovy pill covers those.

If you are comparing this profile against the other approved incretin, our tirzepatide side-effect reference reads that drug's own label the same way, and our head-to-head on the two covers where the trials put them against each other. For what providers actually charge for each, our semaglutide provider rankings and our tirzepatide board carry the price research.

The bottom line

Semaglutide's most common adverse reactions are gastrointestinal, dose-dependent, mostly mild, and reported by roughly three-quarters of adults treated for weight reduction — with severe reactions in 4.1% and treatment discontinuation in 6.8%. Both labels carry a boxed rodent thyroid-tumor warning whose human relevance both labels call unknown, plus warnings for pancreatitis, gallbladder disease, kidney injury from volume depletion, hypersensitivity, and aspiration under anesthesia. Wegovy adds a heart-rate warning that Ozempic's label does not number, and reports severe gastrointestinal reactions at five to ten times Ozempic's rate — a gap driven by dose, population and reporting thresholds rather than by any disagreement about the molecule. The pediatric and 7.2 mg tables report a third and fourth set of numbers again, and none of the four should be quoted as if it were the others.