Drug facts
Semaglutide side effects, and how common they are
Quick answer
The common reactions are gastrointestinal and they are common: nausea in 44% against 16% on placebo, diarrhea in 30% against 16%, vomiting in 24% against 6%. Every figure below is printed beside its placebo rate, because that is the only way to see what the drug added.
The table1
These are the reactions reported in 2% or more of adults treated with semaglutide 2.4 mg for weight reduction, and more often than on placebo. The trial arm was 2,116 people against 1,261 on placebo.
| Reaction | Wegovy | Placebo | Difference |
|---|---|---|---|
| Nausea | 44% | 16% | +28 pts |
| Diarrhea | 30% | 16% | +14 pts |
| Vomiting | 24% | 6% | +18 pts |
| Constipation | 24% | 11% | +13 pts |
| Abdominal pain | 20% | 10% | +10 pts |
| Headache | 14% | 10% | +4 pts |
| Fatigue | 11% | 5% | +6 pts |
| Dyspepsia | 9% | 3% | +6 pts |
| Dizziness | 8% | 4% | +4 pts |
| Abdominal distension | 7% | 5% | +2 pts |
| Eructation | 7% | <1% | +6–7 pts |
| Hypoglycemia (in type 2 diabetes) | 6% | 2% | +4 pts |
| Flatulence | 6% | 4% | +2 pts |
| Gastroenteritis | 6% | 4% | +2 pts |
| Gastroesophageal reflux disease | 5% | 3% | +2 pts |
| Gastritis | 4% | 1% | +3 pts |
| Viral gastroenteritis | 4% | 3% | +1 pts |
| Hair loss | 3% | 1% | +2 pts |
| Dysesthesia (altered skin sensation) | 2% | 1% | +1 pts |
Why the placebo column is the point1
Read the constipation row on its own and 24% looks alarming. Read it beside 11% on placebo and it is still the drug’s doing, but less than half the figure suggests. Read the headache row — 14% against 10% — and most of it is not the drug at all.
Most pages answering this question publish the first column only. A rate without its comparator is not a finding, and the difference column above is arithmetic on the label’s own numbers rather than anything this site has added.
What made people stop1
Discontinuation is a more honest measure of how a drug is tolerated than any single rate, because it counts the people for whom it was bad enough to matter. The reactions leading to it most often were nausea (1.8% against 0.2% on placebo), vomiting (1.2% against 0%) and diarrhea (0.7% against 0.1%).
Those are small numbers against a 44% nausea rate, which is the useful shape of the answer: most people who feel sick do not stop, and the label describes the gastrointestinal reactions as arising mainly during dose escalation — which is what the four-week steps exist to manage.
Serious reactions the label warns about2
The table above is the common reactions. The serious ones sit in a separate part of the label, section 5, as warnings rather than as ranked rates. Four of them involve the digestive system or follow from it:
- Acute pancreatitis. The label describes persistent or severe abdominal pain, sometimes radiating to the back, with or without nausea or vomiting, and says to discontinue the drug if pancreatitis is suspected. It was confirmed in 4 people on semaglutide and 1 on placebo in the weight-reduction trials. The symptoms, in the label’s words
- Acute gallbladder disease. Gallstones were reported by 1.6% of adults on the injection against 0.7% on placebo, and gallbladder inflammation by 0.6% against 0.2%.
- Acute kidney injury from dehydration. Most of the cases reported after approval followed nausea, vomiting or diarrhea severe enough to cause dehydration. What the label says about diarrhea
- Severe gastrointestinal reactions. Reported by 4.1% of adults on the injection against 0.9% on placebo.
The same section also covers thyroid C-cell tumors, low blood sugar, serious allergic reactions, diabetic eye complications, a raised resting heart rate, and aspiration during anesthesia.
What this means for a compounded vial1
On the label — Wegovy / Ozempic
These rates come from trials of the approved product, at a known dose, in a defined population, with adverse events collected systematically.
In a compounded vial
No equivalent table exists. A compounded preparation has run no trial of its own, so the honest position is that these are the best available figures for the molecule and not measurements of the vial you were sent.
Sources
- FDA prescribing information for WEGOVY (semaglutide), revision 6/2026 DailyMed
- FDA prescribing information for WEGOVY (semaglutide), sections 5 and 6.1, revision 6/2026 DailyMed
The label’s own table, not a complete safety assessment: rarer reactions are not on it, and anything you notice is for your prescriber.