Is Semaglutide Safe? Side Effects, Warnings and Who Should Not Take It

The finding that still shapes the label came from lifetime studies in mice and rats, where semaglutide caused a dose-dependent and treatment-duration-dependent increase in thyroid C-cell tumors at clinically relevant exposures. The prescribing information is explicit that it is unknown whether this happens in humans, because the human relevance of the rodent finding has not been determined. Reproductive studies in rats, rabbits and cynomolgus monkeys reported embryofetal effects and early pregnancy losses at exposures at or below the maximum human dose, coinciding with marked maternal weight loss. That is the basis for the pregnancy position.

STEP 1, published in the New England Journal of Medicine in 2021, randomized 1,961 adults with overweight or obesity and no diabetes to semaglutide 2.4 mg weekly or placebo for 68 weeks. Nausea and diarrhea were the most common adverse events, described as typically transient and mild to moderate, and 4.5% of the semaglutide group versus 0.8% on placebo discontinued because of gastrointestinal events. STEP 2 (The Lancet, 2021) repeated the design in adults with type 2 diabetes, STEP 3 (JAMA, 2021) added intensive behavioral therapy, STEP 4 (JAMA, 2021) studied switching to placebo, STEP 5 (Nature Medicine, 2022) ran two years, and STEP 8 (JAMA, 2022) compared semaglutide with daily liraglutide. The Wegovy label pools three of these, 2,116 adults on 2.4 mg for up to 68 weeks, for its adverse-reaction table.

The largest single safety dataset is SELECT (New England Journal of Medicine, 2023): 17,604 adults aged 45 or older with established cardiovascular disease and a body-mass index of 27 or more, without diabetes, followed for a mean of 39.8 months. The primary result was a lower rate of major adverse cardiovascular events on semaglutide (6.5% versus 8.0%, hazard ratio 0.80). For safety, the important numbers are exposure and discontinuation: mean exposure was 34.2 months, and adverse events led to permanent discontinuation in 16.6% of the semaglutide group versus 8.2% on placebo. SELECT is where the fracture, urolithiasis and serious hypoglycemia observations on the current label come from.

SUSTAIN-6 (New England Journal of Medicine, 2016) was the cardiovascular outcomes trial at diabetes doses and is the source of the diabetic retinopathy signal. FLOW (New England Journal of Medicine, 2024) randomized 3,533 adults with type 2 diabetes and chronic kidney disease to semaglutide 1 mg or placebo for a median of 3.4 years and reported serious adverse events in a lower percentage of the semaglutide group than placebo (49.6% versus 53.8%).

Post-marketing reports arrive voluntarily from a population of uncertain size, so frequencies cannot be estimated from them. The current label's post-marketing section lists acute and necrotizing pancreatitis; ileus, intestinal obstruction and severe constipation including fecal impaction; anaphylaxis, angioedema, rash and urticaria; pulmonary aspiration during anesthesia; and acute kidney injury. Each has since been written into the warnings, which is how a label is supposed to evolve.

Every number above belongs to the branded product. A compounded preparation contains the same active ingredient, so the molecule's risk profile carries across; the manufacturing specification, stability data and regulatory review do not.

"Common" is vague, so here are the rates from the pooled adult trials on the current Wegovy label, semaglutide 2.4 mg versus placebo: nausea 44% versus 16%, diarrhea 30% versus 16%, vomiting 24% versus 6%, constipation 24% versus 11%, abdominal pain 20% versus 10%, headache 14% versus 10%, fatigue 11% versus 5%, dyspepsia 9% versus 3%, dizziness 8% versus 4%, abdominal distension 7% versus 5%, belching 7% versus under 1%, flatulence 6% versus 4%, reflux disease 5% versus 3%. Overall, 73% of semaglutide-treated adults and 47% of placebo-treated adults reported some gastrointestinal reaction. The placebo column matters: a fair share of the nausea and fatigue reported on semaglutide happens on placebo too, because people changing their diet feel these things.

In the pooled trials, 6.8% of semaglutide-treated adults and 3.2% on placebo permanently stopped because of adverse reactions; the gastrointestinal share was 4.3% versus 0.7%, and severe gastrointestinal reactions were 4.1% versus 0.9%. In SELECT, with far longer exposure and an older population with heart disease, 16.6% versus 8.2% stopped for an adverse event. So most people tolerate semaglutide, a minority stop because of it, and the share who stop rises with duration and age.

Hair loss was 3.3% on semaglutide 2.4 mg versus 1% on placebo, almost entirely in women, and the label attributes it to weight reduction rather than the drug. Altered taste was 1.7% versus 0.5%, injection-site reactions 1.4% versus 1.0%, low blood pressure 1.3% versus 0.4% and fainting 0.8% versus 0.2%, the last two more frequent in people already on blood-pressure medication.

The boxed warning says, in substance, that semaglutide causes thyroid C-cell tumors in rodents at clinically relevant exposures; that it is unknown whether it does so in humans; and that it is contraindicated with a personal or family history of medullary thyroid carcinoma or with MEN 2. The label adds that cases of medullary thyroid carcinoma reported in people taking liraglutide, another GLP-1 receptor agonist, are insufficient to establish or exclude a causal link.

Acute pancreatitis was confirmed by adjudication in 4 semaglutide-treated adults in the pooled trials (0.2 cases per 100 patient-years) versus 1 on placebo. If pancreatitis is suspected, semaglutide should be stopped promptly, and if confirmed, not restarted. Trial experience in people with prior pancreatitis is limited and it is unknown whether they are at higher risk, which is why that history is a discussion rather than an automatic refusal. Amylase and lipase rise on treatment (mean increases of 15 to 16% and 39%) without symptoms, so a raised enzyme alone is not diagnostic.

Gallstones were reported by 1.6% on semaglutide versus 0.7% on placebo, and cholecystitis by 0.6% versus 0.2%. Rapid weight loss itself raises gallstone risk, but the label notes the excess on semaglutide persisted even after accounting for the degree of weight loss. A systematic review in JAMA Internal Medicine in 2022 pooled 76 randomized trials of the GLP-1 class and reported a relative risk of 1.37 for gallbladder or biliary disease, higher at higher doses and with longer use, and highest in weight-loss trials. Right upper abdominal pain, fever or jaundice is the presentation to act on.

This section was added to the Wegovy label in October 2025. It records that severe gastrointestinal reactions were reported in 4.1% versus 0.9% of adults, that ileus, intestinal obstruction and severe constipation including fecal impaction have been reported post-marketing, and that semaglutide is not recommended in people with severe gastroparesis. A 2023 research letter in JAMA using a large claims database reported higher rates of pancreatitis, bowel obstruction and gastroparesis among people using GLP-1 agonists for weight loss than among users of an older weight-loss drug. Constipation that stops responding, or distension with vomiting, is not something to push through.

Acute kidney injury occurred in 7 semaglutide-treated adults (0.4 per 100 patient-years) versus 4 on placebo, and there are post-marketing reports of kidney injury, some requiring dialysis, most in people whose nausea, vomiting or diarrhea led to dehydration. The August 2025 revision retitled this section "Acute Kidney Injury Due to Volume Depletion" to make the mechanism explicit. Risk was higher in people with existing kidney impairment and during titration. The prevention is unglamorous: drink, and report vomiting that lasts more than a day.

On its own, semaglutide lowers glucose in a glucose-dependent way and rarely causes hypoglycemia. Combined with insulin or a sulfonylurea the risk rises, and the label advises considering a dose reduction of those drugs when starting. In the trial of adults with type 2 diabetes, clinically significant hypoglycemia was 6.2% versus 2.5%. In people without diabetes, serious hypoglycemia was rare in SELECT, but the label singles out a history of bariatric surgery as a risk factor.

Anaphylaxis and angioedema have been reported and are the second contraindication: a prior serious hypersensitivity reaction to semaglutide or any excipient. Facial or throat swelling or breathing difficulty is an emergency first and a phone call second.

In SUSTAIN-6, retinopathy complications occurred in 3.0% on semaglutide versus 1.8% on placebo, with the excess concentrated in people who already had retinopathy at baseline (8.2% versus 5.2%). The label attributes this to the known temporary worsening that accompanies rapid improvement in glucose control rather than to a direct drug effect, and asks that people with a history of diabetic retinopathy be monitored. If you do not have diabetes, this warning does not apply to you.

Mean resting heart rate rose 1 to 4 beats per minute versus placebo, and more semaglutide-treated adults had a maximum increase of 20 bpm or more at some visit (26% versus 16%). The label asks for heart rate to be checked at routine intervals, for palpitations at rest to be reported, and for discontinuation if a sustained increase occurs.

Because semaglutide slows gastric emptying, there are rare post-marketing reports of stomach contents being present at surgery despite standard fasting, with aspiration during general anesthesia or deep sedation. The label states that data are insufficient to say whether longer fasting or temporarily stopping the drug reduces this, and instructs patients to tell the team before any planned procedure. Colonoscopy sedation counts. Tell the anesthetist; do not decide to stop it yourself.

The FDA's page on unapproved GLP-1 drugs, current as of 1 September 2026, records that the agency received multiple adverse event reports, some requiring hospitalization, that may be related to dosing errors with compounded injectable semaglutide, and that these "resulted from patients measuring and self-administering incorrect doses of the drug, and in some cases, health care professionals miscalculating doses." It also records reports of compounded semaglutide or tirzepatide prescribed at doses beyond the approved label, as a larger single dose, more frequent dosing or a faster escalation. The root cause is that a manufactured pen delivers a fixed dose with a click, while a compounded vial is drawn in an insulin syringe marked in units from a vial whose concentration varies by product. This is why Pepti's directions are printed in milliliters and units for the specific vial you are sent, why the concentration is on the label, and why the pepti Pen exists as a click-dosed alternative.

The same FDA page states that some compounders have used semaglutide sodium or semaglutide acetate, that these salts "are different active ingredients than are used in the approved drugs," that the agency has no information on whether they share the approved ingredient's properties, and that it is not aware of any lawful basis for their use in compounding. A legitimate preparation uses semaglutide base, the same active ingredient as the approved products, and the pharmacy can show that on the certificate of analysis.

Three things: the identity of the state-licensed, FDA-registered pharmacy that compounded it; a certificate of analysis covering identity, purity and sterility, of the kind published at lab results; and a label carrying the concentration and beyond-use date. The quality page describes what Pepti verifies before a product ships, and is compounded semaglutide safe is the full checklist. What it does not carry is FDA approval, and any seller who says otherwise is misrepresenting it.

Semaglutide is the active ingredient of three approved products from one manufacturer: Ozempic and Rybelsus for type 2 diabetes, and Wegovy for weight management, for cardiovascular risk reduction in adults with established heart disease and overweight or obesity, and, since 2025, for noncirrhotic MASH with moderate to advanced fibrosis under accelerated approval. Wegovy now exists as an injection and as a tablet, and its prescribing information was last revised in June 2026.

Semaglutide injection was on the FDA drug shortage list from 2022, which is what allowed large-scale compounding of copies. The FDA's compounding-policy page, current as of 1 April 2026, states that "tirzepatide and semaglutide do not currently appear on the 503B bulks list or on FDA's drug shortage list," that the enforcement-discretion period for 503A pharmacies compounding semaglutide has ended, and that the 503B outsourcing-facility grace period ended on 22 May 2025. What remains is ordinary 503A compounding: a state-licensed pharmacy may compound semaglutide for an individual patient on a prescription, provided the product is not "essentially a copy" of a commercially available drug, meaning the same active ingredient in the same or similar strength by the same route, unless the prescriber documents a change that produces a significant difference for that patient. That is why compounded semaglutide today is prescribed at physician-determined strengths on an individual prescription, and why it cannot be marketed as a generic Wegovy.

Compounded semaglutide is not FDA approved. The FDA does not review compounded drugs for safety, effectiveness or quality; what stands behind a compounded preparation is the pharmacy's state license, its FDA registration, its testing and the physician's prescription. Wegovy and Ozempic are approved; a compounded vial containing the same active ingredient is not, and that is the correct way to describe it.