Quick answer: The common semaglutide side effects are digestive: nausea, diarrhea, vomiting, constipation and stomach pain. On Wegovy 2.4 mg, the weight-loss dose, 44% of adults in the trials had nausea against 16% on placebo, and 73% had some digestive side effect against 47% on placebo. They are most common while the dose is being raised and usually ease once it holds steady. Serious problems such as pancreatitis and gallbladder disease are uncommon, and each is a reason to call your prescriber the same day.
Semaglutide is one medicine sold under two brand names: Ozempic, for type 2 diabetes, and Wegovy, for chronic weight management. Both come as a weekly injection, and both now also come as a tablet. The side effects are the same kind whichever brand you use. How often they happen depends mainly on the dose, which is why the Wegovy figures below are higher than the Ozempic ones. Every number on this page comes from the FDA prescribing information, not from patient forums.
How common is each semaglutide side effect?
This is Table 3 of the Wegovy label: three placebo-controlled trials in 2,116 adults with obesity or overweight who took 2.4 mg a week for up to 68 weeks. It lists every reaction reported by at least 2% of people on Wegovy and more often than on placebo.
| Side effect | Placebo | Wegovy 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 (eructation) | under 1% | 7% |
| Low blood sugar, in people with type 2 diabetes | 2% | 6% |
| Gas (flatulence) | 4% | 6% |
| Gastroenteritis | 4% | 6% |
| Reflux (GERD) | 3% | 5% |
| Gastritis | 1% | 4% |
| Viral gastroenteritis | 3% | 4% |
| Hair loss | 1% | 3% |
| Skin sensitivity (dysesthesia) | 1% | 2% |
In the same trials, 6.8% of people on Wegovy stopped because of side effects, against 3.2% on placebo. The most common reasons were nausea (1.8%), vomiting (1.2%) and diarrhea (0.7%). Severe digestive reactions were reported by 4.1% on Wegovy and 0.9% on placebo.
Ozempic side effects: lower doses, lower rates
Ozempic's label pools two placebo-controlled trials in adults with type 2 diabetes at 0.5 mg and 1 mg a week, well below the Wegovy dose. The same digestive effects lead the list, at lower rates:
| Side effect | Placebo | Ozempic 0.5 mg | Ozempic 1 mg |
|---|---|---|---|
| Nausea | 6.1% | 15.8% | 20.3% |
| Vomiting | 2.3% | 5.0% | 9.2% |
| Diarrhea | 1.9% | 8.5% | 8.8% |
| Abdominal pain | 4.6% | 7.3% | 5.7% |
| Constipation | 1.5% | 5.0% | 3.1% |
Digestive side effects of any kind affected 15.3% on placebo, 32.7% on 0.5 mg and 36.4% on 1 mg. In a trial that compared 1 mg with 2 mg, they affected 30.8% and 34%. Taken with insulin or a sulfonylurea, Ozempic raises the risk of low blood sugar, which is why the dose of those medicines is often lowered when it starts.
How long do semaglutide side effects last?
Both labels say the same thing about timing: most reports of nausea, vomiting and diarrhea came during dose escalation, the first months when the dose steps up every four weeks. For most people they ease once the dose holds steady. Neither label gives a number of days, so be wary of anyone who promises one.
If a side effect is still strong after a few weeks at the same dose, staying longer at that dose, or stepping back down, is a normal part of treatment. That is your prescriber's call to make with you, not a reason to stop on your own. The full escalation schedule is in our semaglutide dosage chart, and the semaglutide dose calculator converts a dose to syringe units.
What helps with nausea, constipation and diarrhea?
- Eat smaller meals, slowly, and stop at the first sign of fullness. Semaglutide slows how fast the stomach empties, so a normal-sized meal can sit heavily.
- Go easy on greasy, fried and very sweet foods, especially in the days after a dose increase.
- Drink fluids through the day. Vomiting and diarrhea can dehydrate you, and the label warns that dehydration can injure the kidneys.
- For constipation: fluids, fiber and daily movement first, then ask about a stool softener before it builds up.
- For reflux and burping: don't lie down for a couple of hours after eating.
- Keep protein up while your appetite is low. Our GLP-1 protein calculator gives a daily target.
Serious side effects: when to call
These are uncommon, but the labels list each one as a warning. Call your prescriber the same day, or get emergency care if symptoms are severe:
- Pancreatitis: severe stomach pain that does not go away, sometimes spreading to the back, with or without vomiting. In the Wegovy trials it was confirmed in 4 people on Wegovy (0.2 cases per 100 patient-years) and 1 on placebo.
- Gallbladder problems: pain in the upper right belly, fever, yellow skin or eyes, or pale stools. Gallstones were reported by 1.6% on Wegovy and 0.7% on placebo, and gallbladder inflammation by 0.6% and 0.2%.
- Dehydration and kidney injury: dizziness when you stand, dark urine or passing very little, usually after days of vomiting or diarrhea.
- Low blood sugar, if you also take insulin or a sulfonylurea: shakiness, sweating, confusion, a fast heartbeat.
- Allergic reactions: swelling of the face, lips, tongue or throat, trouble breathing or swallowing, or a severe rash.
- Vision changes, if you have diabetic retinopathy.
- A racing heartbeat at rest. On average resting heart rate rose 1 to 4 beats a minute.
- Mood changes: new or worsening depression, or thoughts of self-harm. The Wegovy label says to stop treatment if they appear.
- A lump or swelling in the neck, trouble swallowing or a hoarse voice that lasts (see the thyroid warning below).
- Before any surgery or sedation, tell the doctor you take semaglutide: food can stay in the stomach longer, and the labels report food entering the lungs under anesthesia.
Who should not take semaglutide?
The labels rule semaglutide out for anyone with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2 (MEN 2), and for anyone who has had a serious allergic reaction to semaglutide. Their boxed warning explains why: semaglutide caused thyroid C-cell tumors in rats and mice, and it is not known whether it does in people. Wegovy's label also advises avoiding it with a history of suicide attempts, and stopping it at least 2 months before a planned pregnancy because semaglutide stays in the body for weeks.
Hair loss, Ozempic face and other questions people ask
Hair loss was reported by 3% on Wegovy against 1% on placebo; we explain why it happens and what helps in Wegovy hair loss and GLP-1 hair loss. Loss of facial volume after fast weight loss has its own guide: Ozempic face. What changes when treatment ends is in what happens when you stop semaglutide, and if you are weighing the other weekly medicine, see tirzepatide side effects.
Do semaglutide side effects go away?
For most people the digestive side effects ease. Both labels report that most nausea, vomiting and diarrhea came during dose escalation, so they tend to settle once the dose is stable. If a side effect stays strong for weeks at one dose, ask your prescriber about holding or stepping back a dose.
Are Ozempic and Wegovy side effects the same?
They are the same medicine, so the side effects are the same kind. Wegovy is dosed higher, up to 2.4 mg a week, so its rates are higher: nausea in 44% of people on Wegovy against 16% to 20% on Ozempic 0.5 mg or 1 mg.
What side effects can I expect after the first dose?
The first dose, 0.25 mg, is a starting dose meant to let your stomach adjust, not a treatment dose. Some people notice mild nausea, fullness or less appetite in the first few days; many notice little. The higher rates in the labels cover the whole escalation period.
Can semaglutide affect your mood?
The Wegovy label asks prescribers to watch for depression and suicidal thoughts and to stop treatment if they appear, and advises avoiding it after a suicide attempt. Tell your prescriber about any history of depression before you start.
Does semaglutide cause hair loss?
In some people. The Wegovy label reports hair loss in 3% on Wegovy against 1% on placebo. It is usually shedding that follows rapid weight loss and eating too little, and it typically recovers.
Starting semaglutide in California
If you live in California, your first consultation can be by video, with labs and medication pickup at our Mission Viejo clinic. Lindsay Short, NP-BC, goes through your history, including the conditions above, before anything is prescribed. Read how the program works on our GLP-1 weight loss page.
References
- Wegovy (semaglutide) injection prescribing information: Table 3, adverse reactions; sections 4, 5 and 8.1 — Novo Nordisk, FDA label via DailyMed
- Ozempic (semaglutide) injection prescribing information: Table 1 and Table 2, adverse reactions; section 5 — Novo Nordisk, FDA label via DailyMed
- Wilding JPH et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med 2021;384:989-1002 — New England Journal of Medicine