Semaglutide side effects: what is common and what is serious

How often each side effect showed up

The best numbers for semaglutide come from the FDA label tables, which compare the drug with placebo. The figures below are for Wegovy 2.4 mg in adults in the weight trials, Section 6.1 of the label ^[1]. Ozempic, the diabetes brand, uses lower doses, and its rates were lower: nausea was 15.8% on 0.5 mg and 20.3% on 1 mg, compared with 6.1% on placebo ^[2].

Semaglutide 2.4 mg (Wegovy) vs placebo, adult weight trials

Side effect	Semaglutide 2.4 mg	Placebo
Nausea	44%	16%
Diarrhea	30%	16%
Vomiting	24%	6%
Constipation	24%	11%
Abdominal pain	20%	10%
Headache	14%	10%
Fatigue	11%	5%
Dyspepsia (indigestion)	9%	3%
Dizziness	8%	4%
Hair loss	3.3%	1%

The label also lists bloating (abdominal distension), burping (eructation), gas, stomach flu (gastroenteritis) and reflux (GERD) as more frequent on semaglutide than placebo ^[1]. For the full picture across GLP-1 drugs, see our GLP-1 side effects guide.

Hair loss, tiredness, headaches and dizziness

Hair loss. It was reported in 3.3% of adults on 2.4 mg and 1% on placebo, rising to 5.8% at the 7.2 mg dose; in teens 12 and older it was 4% vs 0% ^[1]. The label does not explain why it happens. If you notice shedding, raise it with your prescriber. Our guide to protein and muscle on a GLP-1 covers nutrition questions people often ask at the same time.

Fatigue. Tiredness affected 11% of adults on semaglutide 2.4 mg vs 5% on placebo ^[1]. The label makes no claim that semaglutide gives you energy. If fatigue comes with vomiting or diarrhea that will not stop, tell your prescriber, because losing fluids can lead to kidney injury (label Section 5.5) ^[1].

Headache and dizziness. Headache was reported by 14% vs 10%, and dizziness by 8% vs 4% ^[1]. In people with type 2 diabetes, dizziness or shakiness can also be a sign of low blood sugar, which is more likely with insulin or a sulfonylurea ^[1].

Nausea, diarrhea, constipation and heartburn

Gut and bowel trouble is what most often ends treatment. Per the Wegovy label, 6.8% of adults on 2.4 mg quit because of a side effect, against 3.2% on placebo; nausea (1.8%), vomiting (1.2%) and diarrhea (0.7%) led the list ^[1].

Why does it happen? The label states that semaglutide slows how fast the stomach empties ^[1]. It does not give a fuller explanation for nausea or diarrhea, and we will not guess at one.

What helps, per the label: if a new dose step is not tolerated, the prescriber can consider delaying the next increase by 4 weeks (Section 2) ^[1]. Do not change your dose on your own. Heartburn and indigestion (dyspepsia 9% vs 3%) and reflux are listed reactions too ^[1]. Severe constipation, including fecal impaction, and intestinal blockage (ileus) have been reported after approval (Section 6.2) ^[1].

When side effects start and how long they last

The Wegovy label says stomach reactions were reported most often during dose escalation, the first 16 weeks when the dose steps up every 4 weeks ^[1]. In the STEP 1 trial, nausea and diarrhea were the most common events and were typically temporary and mild to moderate; 4.5% stopped for stomach events vs 0.8% on placebo ^[3].

Neither the label nor the STEP 1 abstract gives a set number of days that nausea lasts. If symptoms are not easing, or you cannot keep fluids down, call your prescriber. For what to do when you stop, see what happens when you stop semaglutide.

Serious risks to know about

• Pancreatitis. Confirmed acute pancreatitis occurred at 0.2 cases per 100 patient-years on Wegovy vs under 0.1 on placebo; necrotizing and fatal cases have been reported after approval ^[1]. There is no label method to prevent it. Know the sign: severe stomach pain that does not go away ^[4].
• Gallbladder problems. Gallstones occurred in 1.6% of adults on the injection vs 0.7% on placebo, and gallbladder inflammation in 0.6% vs 0.2% ^[1].
• Low blood sugar. In people with type 2 diabetes, 6.2% had clinically significant low blood sugar vs 2.5% on placebo; the risk is higher with insulin or sulfonylureas ^[1].
• Kidney injury from dehydration after vomiting or diarrhea (Section 5.5) ^[1].
• Eye changes in type 2 diabetes. The label warns about diabetic retinopathy complications (Section 5.8) ^[1].
• Faster heart rate. Resting heart rate rose 1 to 4 beats per minute on average vs placebo (Section 5.9) ^[1].
• Food in the lungs during anesthesia. Tell every surgeon and anesthesia team you take semaglutide (Section 5.10) ^[1].
• Serious allergic reactions, including anaphylaxis and angioedema, reported after approval ^[1].

Cancer, depression and other worries

Cancer. The only cancer signal on the label is a boxed warning about the thyroid. In rodent studies, semaglutide caused thyroid C-cell tumors, and no one yet knows if the drug does this in humans, medullary thyroid carcinoma (MTC) included ^[1]. People with MEN 2, or a personal or family history of MTC, are told not to use it ^[1]. No other cancer is listed as a known risk.

Depression and anxiety. The suicidal behavior and ideation warning was removed from the Wegovy and Zepbound labels in February 2026 ^[5]. Anxiety, depression, insomnia and erectile dysfunction are not among the adverse reactions we found in the Wegovy label's Section 6.1. Mood changes still deserve a call to your prescriber, and if you have thoughts of harming yourself, call 911.

Other questions we could not confirm in the label: effects on periods, feeling cold, body aches, blood clots, peeing more and yeast infections. We did not find these in the label sections we reviewed, so we cannot give a rate. Thirst can come from fluid loss when vomiting or diarrhea is severe, which the label links to kidney injury ^[1].

Compounded semaglutide and Rybelsus

Compounded semaglutide is not FDA-approved, and FDA does not review compounded drugs for safety, effectiveness or quality ^[6]. As of May 31, 2026, FDA had received 990 adverse event reports tied to compounded semaglutide, and it has warned about dosing errors from mismeasured doses and miscalculated units, some leading to hospital care ^[6]. The label rates in this guide come from trials of the branded drug and may not apply. Read more in compounded semaglutide, and check vial handling and discard dates in how to store semaglutide.

Rybelsus is another semaglutide medicine from Novo Nordisk ^[7]. Its current label was out of reach for this update, so this page quotes none of its rates. The 25 mg Wegovy tablet, a different product approved for weight, produced reactions that the Wegovy label describes as similar in type and frequency to the 2.4 mg shot ^[1].

Injection technique questions, including injecting in the stomach, are covered in how to use semaglutide. Cost and program details are in semaglutide cost, and brand-specific detail is in Wegovy side effects and Ozempic side effects.