Semaglutide Side Effects: 18 Adverse Reactions by Dose

The most common semaglutide side effects are gastrointestinal: in the adult Wegovy 2.4 mg weight-reduction trials, nausea affected 44% of patients, diarrhea 30%, vomiting 24%, and constipation 24%, versus 16%, 16%, 6%, and 11% on placebo.¹ Most are mild to moderate and cluster during the 16-week dose-escalation window. Serious semaglutide side effects exist but are uncommon: acute pancreatitis, acute kidney injury from dehydration, gallbladder disease, anaphylaxis, and the boxed-warning thyroid C-cell tumor risk.¹ This breakdown covers the FDA-approved adverse reaction tables for Wegovy 2.4 mg, the newer Wegovy HD 7.2 mg, and Ozempic, sorted by incidence and flagged when a reaction is serious enough to watch.

Wegovy (semaglutide for chronic weight management and cardiovascular risk reduction) carries the cleanest rate data, since its trials were designed for a broad obesity population rather than type 2 diabetes. Ozempic (same molecule, FDA-approved for type 2 diabetes) has a distinct rate profile because its trial population and dose range differ. Rybelsus (oral semaglutide tablet) shares the underlying safety profile. Compounded semaglutide side effects are covered at the end; the active molecule is the same, and class-level reactions are expected, but rate data of trial quality does not exist for compounded preparations. Clinical decisions belong with a licensed prescriber.

What are the most common semaglutide side effects?

The FDA-approved Wegovy label reports the following adverse reaction rates from 3 randomized, double-blind, placebo-controlled trials that enrolled 2,116 adult patients on Wegovy 2.4 mg once weekly and 1,261 placebo patients for up to 68 weeks.¹

Source: Wegovy Full Prescribing Information, Section 6.1 Clinical Trials Experience, Table 3. Adverse reactions reported in ≥2% of Wegovy 2.4 mg injection-treated adults and more frequently than placebo, pooled from 3 weight-reduction trials.¹

Three observations sit under this table. First, gastrointestinal reactions dominate; the top five adverse reactions are all GI or GI-adjacent. Second, placebo rates are not zero; 16% of placebo patients reported nausea and 16% reported diarrhea, so the drug-attributable nausea rate is closer to 28 percentage points, not the raw 44%. Third, any-GI-reaction rates are very high: 73% of adult Wegovy 2.4 mg patients and 47% of placebo patients reported at least one gastrointestinal adverse reaction during the trials.¹ Most patients on semaglutide will experience at least one GI reaction, even if mild.

How common is nausea on semaglutide?

Nausea is the single most common semaglutide side effect. In the pooled adult Wegovy 2.4 mg trials, nausea was reported by 44% of semaglutide-treated patients versus 16% of placebo-treated patients.¹ The placebo-adjusted rate, the nausea attributable to the drug, is roughly 28 percentage points.

The Wegovy label is explicit that gastrointestinal reactions "were most frequently reported during dosage escalation."¹ Mechanistically, semaglutide slows gastric emptying, so food stays in the stomach longer. That delayed emptying produces the fullness signal that drives appetite reduction, and it also triggers nausea in susceptible patients. The stomach adapts over weeks, which is why nausea tends to fade once a patient is on a stable dose for long enough to reach steady-state plasma semaglutide.

At the higher 7.2 mg dose (Wegovy HD), nausea was reported by 39% of patients versus 35% at 2.4 mg and 13% at placebo.¹ That incremental 4-point rise for a 3-fold dose increase suggests the nausea response plateaus after 2.4 mg. In the Ozempic trials in type 2 diabetes, nausea rates were lower: 15.8% at 0.5 mg, 20.3% at 1 mg, and 6.1% on placebo.² Ozempic uses a lower dose range, starts at 0.25 mg for 4 weeks as a tolerance-only step, and tops out at 2 mg weekly.

How common is diarrhea, vomiting, and constipation on semaglutide?

After nausea, the other three major gastrointestinal semaglutide side effects follow clear rates in the Wegovy label data.¹

• Diarrhea: 30% on Wegovy 2.4 mg versus 16% on placebo. Diarrhea is reported by nearly a third of patients, but the placebo rate is unusually high, so the drug-attributable rate is around 14 percentage points.
• Vomiting: 24% on Wegovy 2.4 mg versus 6% on placebo. Vomiting shows the largest placebo-to-drug gap of any GI reaction, and it is the single most common adverse reaction driving discontinuation.
• Constipation: 24% on Wegovy 2.4 mg versus 11% on placebo. Constipation is the reaction that most often persists as a chronic issue after the escalation window, because the underlying motility slowing is ongoing rather than transient.

Clinically, these GI reactions cluster. Patients who get nausea often also get dyspepsia, eructation, GERD, or abdominal pain, all features of slowed gastric emptying. Severe GI reactions (not the everyday reactions above, but reactions rated severe by clinical adjudication) occurred in 4.1% of Wegovy injection-treated adults versus 0.9% of placebo-treated adults.¹ Postmarketing reports on both the Wegovy and Ozempic labels add ileus, intestinal obstruction, and severe constipation including fecal impaction.¹²

What are the serious side effects of semaglutide?

The FDA label describes several rare but clinically important semaglutide side effects. These are not frequent, but they warrant knowing about because they may require urgent evaluation.

Acute pancreatitis

In pooled Wegovy weight-reduction trials, acute pancreatitis was confirmed by adjudication in 4 Wegovy-treated patients (0.2 cases per 100 patient-years) versus 1 placebo-treated patient (less than 0.1 cases per 100 patient-years). One additional case was confirmed in a Wegovy-treated patient in another clinical trial.¹ In Ozempic glycemic-control trials, adjudicated acute pancreatitis occurred in 7 Ozempic-treated patients (0.3 cases per 100 patient-years) versus 3 in comparators (0.2 cases per 100 patient-years).² Postmarketing reports on the Wegovy label include fatal and non-fatal hemorrhagic or necrotizing pancreatitis.¹ Persistent severe abdominal pain, especially radiating to the back, warrants urgent evaluation.

Acute kidney injury from volume depletion

In adult Wegovy 2.4 mg weight-reduction trials, acute kidney injury occurred in 7 semaglutide-treated patients (0.4 cases per 100 patient-years) versus 4 placebo-treated patients (0.2 per 100 patient-years).¹ Some events occurred alongside gastrointestinal reactions or dehydration. The mechanism is usually volume depletion from vomiting, diarrhea, or reduced fluid intake. The risk was higher in patients with pre-existing renal impairment.¹ Staying hydrated through the titration window is a practical protection.

Acute gallbladder disease

In adult Wegovy weight-reduction trials, cholelithiasis (gallstones) was reported by 1.6% of Wegovy injection patients versus 0.7% placebo, and 2.5% of Wegovy tablet patients versus 1% placebo. Cholecystitis (gallbladder inflammation) was reported by 0.6% of Wegovy injection patients versus 0.2% placebo.¹ Pediatric rates were higher: cholelithiasis 3.8% versus 0% on placebo, cholecystitis 0.8% versus 0%. In the Ozempic trials, cholelithiasis was reported in 1.5% and 0.4% of patients on 0.5 mg and 1 mg, with no placebo cases.² Rapid weight loss is a known background risk factor for gallstones independent of the drug.

Hypersensitivity reactions, including anaphylaxis

Serious hypersensitivity reactions, including anaphylaxis, angioedema, rash, and urticaria, appear in the postmarketing reports on both the Wegovy and Ozempic labels.¹² Wegovy is contraindicated in patients with a prior serious hypersensitivity reaction to semaglutide or to any of the Wegovy excipients. Any signs of severe allergic reaction, swelling of the face, lips, or throat, widespread rash, or difficulty breathing, are emergency symptoms.

Diabetic retinopathy complications (patients with type 2 diabetes)

In a trial of adult patients with type 2 diabetes and BMI 27 kg/m² or greater treated for weight reduction, retinal disorders were reported by 6.9% of Wegovy injection patients versus 4.2% of placebo patients. In a separate 2-year trial of once-weekly semaglutide injection in adults with type 2 diabetes and high cardiovascular risk, diabetic retinopathy complications occurred in 3% of semaglutide-treated patients versus 1.8% on placebo.¹ The absolute risk increase was largest in patients with a history of diabetic retinopathy at baseline.

Thyroid C-cell tumors (boxed warning)

Semaglutide carries a boxed warning based on rodent studies showing dose-dependent and treatment-duration-dependent thyroid C-cell tumors in rats and mice. Whether this translates to human risk is unknown. Semaglutide is contraindicated in patients with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia syndrome type 2 (MEN 2).¹²

Pulmonary aspiration during anesthesia

Postmarketing reports on both the Wegovy and Ozempic labels describe pulmonary aspiration in patients taking GLP-1 receptor agonists who underwent elective surgery or procedures requiring general anesthesia or deep sedation.¹² The mechanism is delayed gastric emptying producing retained gastric contents despite pre-operative fasting. Disclose semaglutide to your surgical and anesthesia teams well before any planned procedure.

Does semaglutide cause hair loss?

Yes, hair loss is a documented semaglutide side effect, and it is weight-loss-associated more than drug-specific. In the adult Wegovy 2.4 mg trials, hair loss was reported by 3% of Wegovy-treated patients versus 1% of placebo-treated patients.¹ At the higher 7.2 mg dose, the rate was 6% versus 1% placebo. In the pediatric trial for patients aged 12 and older, hair loss was reported by 4% of Wegovy patients versus 0% placebo.¹ Alopecia also appears in the Ozempic postmarketing reports.²

The pattern is consistent with telogen effluvium, the shedding response that follows rapid or significant weight reduction. Hair loss from weight reduction is typically temporary and resolves over 6 to 12 months once weight stabilizes. The Wegovy label does not report a specific discontinuation rate for hair loss, so this reaction is rarely severe enough on its own to stop treatment.

Does semaglutide cause dysesthesia or altered skin sensations?

Dysesthesia, a catch-all term for altered skin sensations including paresthesia (tingling), burning, hyperesthesia, and allodynia, appeared as a dose-dependent semaglutide side effect in the Wegovy trials. At 2.4 mg, dysesthesia was reported by 2% of patients versus 1% on placebo. At the 7.2 mg dose, the rate jumped to 22% versus 6% at 2.4 mg and 0.3% on placebo.¹ The Wegovy label is explicit that dysesthesia incidence rises with dose and drug levels in the blood.

Among the 288 patients who experienced dysesthesia on 7.2 mg, 2% permanently discontinued, 8% had temporary interruption, and 23% had dose reduction.¹ Most who took action recovered, but 18% of patients who experienced dysesthesia on 7.2 mg did not report recovery during the trial. Of 38 patients who recovered after a dose adjustment and were re-escalated to 7.2 mg, 17 (45%) had recurrence. Dysesthesia is also listed in the Ozempic postmarketing reports.²

Does semaglutide cause injection site reactions?

Injection site reactions are reported, but at a much lower rate than with some other injectable medications. In the Ozempic placebo-controlled trials, injection site reactions (discomfort, erythema) were reported by 0.2% of Ozempic-treated patients.² The Wegovy label does not list injection site reactions in Table 3, which reports reactions at 2% or higher, so the Wegovy rate is below that threshold.

Practical mitigation: rotate injection sites across the abdomen, thigh, and upper arm, the three sites approved on the Wegovy and Ozempic labels. Let the alcohol wipe dry before injecting. If redness persists more than 48 hours, or a reaction spreads beyond the injection site, contact your prescriber. That pattern is not typical and may warrant evaluation. Injection site reactions are one category where compounded semaglutide preparations can diverge from the branded products, because the excipient and buffer mix may differ.

How do Wegovy 2.4 mg and 7.2 mg side effects compare?

The Wegovy HD 7.2 mg dose was evaluated in two 72-week trials including 1,311 patients exposed to 7.2 mg, 304 to 2.4 mg, and 303 to placebo. The adverse reaction pattern changed at the higher dose:¹

Source: Wegovy Full Prescribing Information, Table 4. Adverse reactions reported in ≥2% of Wegovy 7.2 mg injection-treated adults and more frequently than 2.4 mg and placebo.¹

The standout differences at 7.2 mg are dysesthesia (22% versus 6% at 2.4 mg), vomiting (22% vs 16%), and hair loss (6% vs 3%). Nausea rises only slightly (39% vs 35%). Despite the higher adverse reaction rates, discontinuation rates were similar: 5% of patients on 7.2 mg injection, 5% on 2.4 mg, and 2% on placebo permanently discontinued due to adverse reactions.¹ The 7.2 mg dose adds dysesthesia and somewhat more nausea without adding a discontinuation penalty.

How do Ozempic side effects compare to Wegovy?

Ozempic and Wegovy contain the same semaglutide molecule, but the FDA-approved doses differ. Ozempic for type 2 diabetes tops out at 2 mg once weekly; Wegovy for chronic weight management maintenance is 2.4 mg, with a higher-dose 7.2 mg option. Ozempic's adverse reaction rates are lower than Wegovy's because the Ozempic dose range is lower:²

Source: Ozempic Full Prescribing Information, Section 6.1, Table 1. Adverse reactions reported in ≥5% of Ozempic-treated patients with type 2 diabetes in placebo-controlled trials.²

In the pool of Ozempic placebo-controlled trials, gastrointestinal reactions occurred in 15.3% of placebo patients, 32.7% of Ozempic 0.5 mg patients, and 36.4% of Ozempic 1 mg patients. Discontinuation due to GI reactions was 3.1% on 0.5 mg and 3.8% on 1 mg, versus 0.4% placebo.² The same-molecule but lower-dose Ozempic regimen produces roughly half the nausea and one-third the vomiting of Wegovy 2.4 mg. In a separate trial with Ozempic at 1 mg versus 2 mg, any GI reaction rates were 30.8% and 34%; the 2 mg dose adds modestly to the profile.² Ozempic also adds a type-2-diabetes-specific hypoglycemia risk when combined with insulin or a sulfonylurea, not a semaglutide-only effect.

How many people stop semaglutide because of side effects?

In the adult Wegovy 2.4 mg weight-reduction trials, 6.8% of semaglutide-treated patients and 3.2% of placebo-treated patients permanently discontinued because of adverse reactions.¹ The most common adverse reactions driving discontinuation were:

• Nausea: 1.8% versus 0.2% placebo
• Vomiting: 1.2% versus 0%
• Diarrhea: 0.7% versus 0.1%

Any gastrointestinal adverse reaction drove 4.3% of Wegovy injection discontinuations versus 0.7% on placebo.¹ At the higher 7.2 mg dose, GI-driven discontinuation was 3% versus 0.3% placebo. The Wegovy tablet arm (25 mg oral once daily) had discontinuation of 6.9% versus 5.9% on placebo, with GI reactions driving 3.4% versus 2%.¹

In the SELECT cardiovascular outcomes trial, 8,803 patients were exposed to Wegovy injection for a median of 37.3 months. 16% of Wegovy-treated patients versus 8% of placebo-treated patients discontinued study drug due to an adverse event over that longer exposure window.¹ The higher rate reflects the 3-year median exposure rather than a different safety profile.

How long do semaglutide side effects last?

Most semaglutide side effects are mild to moderate and concentrate during the dose-escalation window. The Wegovy label is explicit: gastrointestinal reactions "were most frequently reported during dosage escalation."¹ The Wegovy 2.4 mg titration takes 16 weeks (0.25 mg, 0.5 mg, 1 mg, 1.7 mg, 2.4 mg, each held for 4 weeks). Once a patient reaches a stable maintenance dose and has been on it for at least 4 weeks, GI tolerability typically improves.

A few side effects follow different timelines:

• Nausea, vomiting, diarrhea: concentrate during escalation; most resolve or substantially improve within 8 to 12 weeks of reaching a stable maintenance dose.
• Hair loss: peaks 3 to 6 months after the rate of weight loss is greatest; typically resolves over 6 to 12 months once weight stabilizes.
• Dysesthesia: at the 7.2 mg dose, 18% of affected patients did not report recovery during the trial; dose reduction or interruption tends to speed resolution.¹
• Constipation: can persist chronically because the underlying motility slowing continues; dietary fiber, hydration, and laxatives as needed are standard approaches.

For the underlying dose ladder that the titration timing depends on, see the dosing summary in our semaglutide hub.

How can you reduce semaglutide side effects?

A few practical approaches have support from the Wegovy label's own titration reasoning and standard clinical practice:

Do compounded semaglutide side effects match Wegovy and Ozempic?

The active molecule is the same in compounded and branded semaglutide, so the class-level side effects are expected to be the same: gastrointestinal reactions during escalation, occasional hair loss with weight reduction, the serious reactions in the Wegovy and Ozempic labels. What differs is the surrounding data quality and the formulation specifics.

Compounded preparations can contain different excipients, buffers, preservatives, or combination ingredients (such as semaglutide paired with vitamin B12, cyanocobalamin, or lipotropic blends) that are not in the FDA-approved Wegovy or Ozempic vials. Those differences can produce injection site reactions specific to the compounded formulation or effects attributable to the combination ingredient rather than semaglutide itself. For the current regulatory context, see our compounded semaglutide explainer.

One compounded-specific safety signal is dosing errors. The FDA issued a public alert in July 2024 reporting adverse events, some requiring hospitalization, linked to overdoses of compounded injectable semaglutide.³ The FDA cited two mechanisms: patients self-administering the wrong dose from vials they were unfamiliar with, and health care providers miscalculating the dose. Compounded semaglutide is typically dispensed as a multi-dose vial that requires drawing a specific volume into a syringe, a different workflow than the Wegovy and Ozempic prefilled pens. The FDA noted that unfamiliarity with vial-and-syringe measurement and confusion between units (milliliters, milligrams, "units") contributed to the errors.³

Rate data of trial quality for compounded preparations does not exist, the way it does for branded semaglutide. Patients on compounded formulations should expect roughly the same side-effect profile, confirm the concentration and dosing instructions carefully, report any unusual reactions to the compounding pharmacy and prescriber, and be aware that FAERS (the FDA Adverse Event Reporting System) is available for postmarketing reports on any semaglutide product, branded or compounded.⁴

Frequently Asked Questions

What are the dangers of taking semaglutide?

The serious dangers listed on the Wegovy label are acute pancreatitis, acute kidney injury from volume depletion, acute gallbladder disease, severe gastrointestinal reactions, hypersensitivity including anaphylaxis and angioedema, diabetic retinopathy complications in patients with type 2 diabetes, hypoglycemia when combined with insulin or a sulfonylurea, and a boxed warning for thyroid C-cell tumors based on rodent data.¹ Postmarketing reports also include ileus, intestinal obstruction, and pulmonary aspiration under anesthesia.

When are the worst side effects of semaglutide?

Gastrointestinal reactions were most frequently reported during dosage escalation. The Wegovy 2.4 mg maintenance dose is reached after a 16-week titration (0.25, 0.5, 1, 1.7, 2.4 mg, each held 4 weeks). Nausea, vomiting, and diarrhea typically peak in the first few weeks after each dose increase and decrease once a patient stabilizes at a given dose.¹

Do you gain weight after stopping semaglutide?

Weight regain after stopping is well documented for this drug class; it is a pharmacologic effect rather than a side effect. When semaglutide is discontinued, appetite-suppressant and gastric-emptying effects fade, and weight typically partly returns unless dietary and activity changes are maintained. This is not an adverse reaction on the label; it reflects that chronic weight management medications are designed for ongoing use.

Are semaglutide side effects worse for women?

The Wegovy trial population was 71% female, so the overall rates reflect mostly female data. The label does not break adverse reaction rates out by sex for nausea, vomiting, or diarrhea. Hair loss was the one reaction the Wegovy label flagged as notably more common in women in earlier trials, and telogen effluvium is the established background mechanism, so that skew is expected with any weight-loss medication.

Does semaglutide cause depression or mood changes?

The Wegovy label does not list depression or suicidal ideation as a common adverse reaction in Table 3, but the class carries regulatory monitoring for suicidal behavior or ideation from chronic weight management medications broadly. Patients with a history of depression or suicidal ideation should discuss this with their prescriber before starting semaglutide. New or worsening mood symptoms during treatment warrant prompt clinical attention.

Should you stop semaglutide if side effects are severe?

Severe side effects warrant prompt medical attention rather than independent discontinuation. For severe abdominal pain, persistent vomiting, signs of dehydration, suspected pancreatitis, or anaphylaxis symptoms, contact a clinician urgently. For moderate tolerability issues, the Wegovy label permits holding at the current dose longer before advancing, or reinitiating the titration after a gap. That decision belongs in a conversation with a prescriber.¹

Are semaglutide side effects worse than tirzepatide side effects?

The two drugs produce similar gastrointestinal reactions, with rates that differ by trial design more than by molecule. In the adult tirzepatide (Zepbound) trials, nausea ran 25 to 29% across doses; in the adult Wegovy 2.4 mg trials, nausea ran 44%. The populations and trial lengths differ, so direct comparison is imprecise. For the full comparison, see our semaglutide vs tirzepatide guide and our tirzepatide side effects breakdown.

The Bottom Line

Semaglutide side effects are dominated by gastrointestinal reactions during the 16-week dose-escalation window. In the adult Wegovy 2.4 mg trials, nausea hit 44% of patients, diarrhea 30%, vomiting 24%, and constipation 24%. Most of these are mild to moderate and improve once a patient reaches a stable maintenance dose. Discontinuation due to adverse events ran 6.8% on Wegovy versus 3.2% on placebo. Serious reactions, acute pancreatitis, acute kidney injury, gallbladder disease, anaphylaxis, diabetic retinopathy complications, and the boxed-warning thyroid C-cell tumor risk, exist and warrant monitoring, but are uncommon. The higher 7.2 mg dose adds dysesthesia as a notable dose-dependent signal. Ozempic, which uses a lower dose range for type 2 diabetes, produces roughly half the nausea and one-third the vomiting of Wegovy 2.4 mg.

Before starting, changing, or stopping semaglutide, talk to a licensed prescriber. For the full brand-name overview, see our semaglutide hub. For cost context, our semaglutide cost guide covers 2026 pricing across Wegovy, Ozempic, Rybelsus, NovoCare direct, and compounded. For the regulatory and safety picture on compounded preparations, see our compounded semaglutide explainer.