Semaglutide at the weight-loss dose is sold as Wegovy, and its side effects are measured against placebo in trials that ran for up to 68 weeks. The comparison matters, because nausea, headache and tiredness also turn up in people taking a dummy injection. The drug's share is the gap between the two groups.
This page follows the injection at its usual 2.4 mg weekly dose, with notes on the newer 7.2 mg dose. Whether a smaller dose is gentler is a separate question, taken up in microdosing semaglutide.
What the label counted
The label pools three double-blind weight trials in which 2,116 adults took 2.4 mg for up to 68 weeks [1]. The group averaged 48 years of age, and 71% were women. It lists every reaction seen in at least 2% of people on semaglutide and more often than on placebo.
| Side effect | Placebo | Semaglutide 2.4 mg |
|---|---|---|
| Nausea | 16% | 44% |
| Diarrhea | 16% | 30% |
| Vomiting | 6% | 24% |
| Constipation | 11% | 24% |
| Abdominal pain | 10% | 20% |
| Headache | 10% | 14% |
| Fatigue | 5% | 11% |
| Indigestion (dyspepsia) | 3% | 9% |
| Dizziness | 4% | 8% |
| Bloating (abdominal distension) | 5% | 7% |
| Burping | under 1% | 7% |
| Low blood sugar, in people with type 2 diabetes | 2% | 6% |
| Acid reflux | 3% | 5% |
| Hair loss | 1% | 3% |
Stomach and bowel effects, and when they come
A pooled analysis of STEP 1 to 3 gives the most detail on the stomach record [3]. Among 2,117 adults on semaglutide 2.4 mg, nausea affected 43.9%, diarrhea 29.7%, vomiting 24.5% and constipation 24.2%. The placebo figures were 16.1%, 15.9%, 6.3% and 11.1%.
In that analysis, 99.5% of the stomach events on semaglutide were non-serious and 98.1% were mild to moderate. They were usually transient, and they came most often during or just after a dose increase. The label says the same: these reactions were most frequently reported during dose escalation [1].
A minority of reactions were severe. The label puts severe stomach reactions at 4.1% on the injection and 0.9% on placebo, and it does not recommend semaglutide for people with severe gastroparesis [1].
43.9%
had nausea on semaglutide 2.4 mg, against 16.1% on placebo, STEP 1 to 3 pooled
Wharton 2022
4.3%
stopped semaglutide for good because of a stomach side effect, against 0.7% on placebo
Wegovy label
<1 point
of the extra weight loss on semaglutide was explained by stomach side effects
Wharton 2022
Does nausea explain the weight loss?
A common belief holds that the drug works by making people feel too sick to eat. The pooled STEP analysis tested that directly [3]. Mean weight loss was 9.6% to 17.1% in people without stomach side effects and 11.4% to 17.7% in people with them.
A formal mediation analysis reached the same answer. Of the extra 7.6% to 14.4% weight loss over placebo, less than 1 percentage point ran through stomach side effects. The authors concluded that the weight loss was largely independent of them.
Skin sensations and hair loss
One effect is specific enough to deserve its own line. The label describes dysesthesia, an altered skin sensation such as tingling, burning or sensitive skin [1]. Its frequency rose with the dose and with drug levels in the blood.
In the trials of the 7.2 mg weekly dose, dysesthesia was reported by 22% on 7.2 mg, 6% on 2.4 mg and 0.3% on placebo. Among the 288 people who had it on 7.2 mg, 23% had their dose reduced. Of 38 people later stepped back up to 7.2 mg, 17 had it again.
The label links hair loss to weight reduction [1]. In a pool of three trials it was reported by 3.3% on 2.4 mg, split as 4% of women and 0.9% of men, against 1% on placebo. On 7.2 mg the figure rose to 5.8%, including 8.4% of women.
Uncommon events with a clear signal
Several less common events were recorded more often on semaglutide than on placebo in the adult weight trials. [1] Each is small in absolute terms, and each has a named warning in the label.
| Event | Semaglutide | Placebo |
|---|---|---|
| Gallstones, 2.4 mg injection | 1.6% | 0.7% |
| Gallbladder inflammation, 2.4 mg injection | 0.6% | 0.2% |
| Acute pancreatitis, confirmed by adjudication | 0.2 per 100 patient-years | under 0.1 per 100 patient-years |
| Acute kidney injury | 0.4 per 100 patient-years | 0.2 per 100 patient-years |
| Appendicitis | 0.5% | 0.2% |
| Low blood pressure | 1.3% | 0.4% |
| Fainting (syncope) | 0.8% | 0.2% |
The gallbladder signal held up after the label accounted for how much weight people lost [1]. Rapid weight loss raises gallstone risk on its own, but gallbladder disease was still more frequent on semaglutide.
Kidney injury was mostly tied to dehydration from vomiting or diarrhea. The risk was higher in people with a history of kidney impairment and came more often during dose titration.
Heart rate rose too. Resting heart rate increased by a mean of 1 to 4 beats per minute over placebo [1]. A rise of 20 beats or more at some visit was seen in 26% on semaglutide and 16% on placebo.
What a three-year trial added
SELECT followed 17,604 adults aged 45 or older with heart disease and overweight or obesity but no diabetes. [4] The mean time on semaglutide or placebo was 34.2 months. Major heart events fell, with a hazard ratio of 0.80.
Adverse events led 16.6% of people on semaglutide to stop the drug permanently, against 8.2% on placebo [4]. That is the long-run price of the benefit, and it is roughly double the placebo rate.
The same trial surfaced a fracture signal in two groups [1]. Hip and pelvis fractures were reported in 1% of women on semaglutide against 0.2% on placebo. In people aged 75 and older the figures were 2.4% and 0.6%.
Reports since approval, and one removal
Postmarketing reports come from voluntary reporting, so they cannot give a rate [1]. The label lists pancreatitis, including necrotizing and fatal cases, bowel obstruction and severe constipation with fecal impaction. It also lists anaphylaxis, angioedema and acute kidney injury.
Pulmonary aspiration during anesthesia or deep sedation is the other listed risk. The label asks people to tell their care team before any planned procedure. Its change log also records that the suicidal behavior and ideation warning was removed in January 2026.
What this means
The weight-loss record shows a drug whose common side effects are mostly in the gut, mostly early, and mostly mild. In STEP 1, 4.5% of people on semaglutide stopped because of stomach events, against 0.8% on placebo [2]. The rarer events are the ones worth knowing by their symptoms: severe belly pain, right-side pain after meals, or signs of dehydration.
For the equivalent record on the other weekly shot, see tirzepatide side effects. The older daily injection is covered in liraglutide side effects. What happens to weight once treatment ends is in what happens when you stop taking semaglutide.
Prescribers who offer semaglutide are compared on the weight-loss peptides board. Other options sit on the weight goal page.