How common are GLP-1 side effects?
In the placebo-controlled weight-management trials behind the Wegovy label, 73% of adults on Wegovy injection reported a gastrointestinal side effect, compared with 47% on placebo. In the pooled Zepbound trials the figure was 56% in every dose group, against 30% on placebo. The placebo numbers matter: plenty of digestive complaints happen to people taking nothing, so the meaningful figure is the gap between the two columns.
The table lists reactions from each label's main adverse-reaction table. Zepbound was tested at several maintenance doses, so its column shows the range across those groups. A dash means the reaction is not listed in that label's table.
| Side effect | Wegovy injection vs placebo | Zepbound vs placebo |
|---|---|---|
| Nausea | 44% vs 16% | 25-29% vs 8% |
| Diarrhea | 30% vs 16% | 19-23% vs 8% |
| Vomiting | 24% vs 6% | 8-13% vs 2% |
| Constipation | 24% vs 11% | 11-17% vs 5% |
| Abdominal pain | 20% vs 10% | 9-10% vs 5% |
| Headache | 14% vs 10% | - |
| Fatigue | 11% vs 5% | 5-7% vs 3% |
| Indigestion (dyspepsia) | 9% vs 3% | 9-10% vs 4% |
| Dizziness | 8% vs 4% | 4-5% vs 2% |
| Bloating (abdominal distension) | 7% vs 5% | 3-4% vs 2% |
| Belching (eructation) | 7% vs under 1% | 4-5% vs 1% |
| Gas (flatulence) | 6% vs 4% | 3-4% vs 2% |
| Reflux (GERD) | 5% vs 3% | 4-5% vs 2% |
| Hair loss | 3% vs 1% | 4-5% vs 1% |
| Injection site reactions | 1.4% vs 1% | 6-8% vs 2% |
| Hypersensitivity reactions | - | 5% vs 3% |
Can you compare Wegovy and Zepbound using these numbers?
Not directly. Both labels state that adverse-reaction rates from one drug's trials cannot be directly compared with rates in another drug's trials and may not reflect what happens in practice. The trials enrolled different people, ran for different lengths of time and were designed differently. Read each column against its own placebo, not against the other drug.
How many people stop because of side effects?
A small minority. In the Wegovy weight-management trials, 4.3% of adults on Wegovy injection stopped permanently because of a gastrointestinal side effect, versus 0.7% on placebo, and nausea was the single most common reason. In the Zepbound trials, between 1.9% and 4.3% stopped for gastrointestinal reasons depending on dose, versus 0.5% on placebo. The Zepbound label notes that most people who stopped because of side effects did so in the first few months of treatment.
Are GLP-1 side effects usually severe?
Usually not. A pooled analysis of the main semaglutide weight-management trials found that 98.1% of gastrointestinal events were mild to moderate and 99.5% were non-serious. Severe gastrointestinal reactions were still more common than on placebo: 4.1% versus 0.9% for Wegovy injection, and 1.7% to 3.1% versus 1% for Zepbound.
Why GLP-1 medications cause side effects
Two mechanisms explain most of the list. First, both labels state plainly that the medication delays gastric emptying: food leaves the stomach more slowly. Second, GLP-1 receptors sit in areas of the brain involved in appetite regulation, and the labels describe the reduction in calorie intake as likely mediated by effects on appetite. Tirzepatide also acts on GIP receptors, which the Zepbound label says nonclinical studies suggest may add to the regulation of food intake.
Why does slower stomach emptying cause nausea and bloating?
Food that sits in the stomach longer stretches it for longer, and that stretch is signaled to the brain through the vagus nerve. The result is the early fullness, queasiness, bloating, reflux and belching that dominate the table above. A large or rich meal adds to a delay the medication has already created, which is why meal size and fat content come up in almost every piece of practical advice.
It is also why both labels say the medications are not recommended for people with severe gastroparesis, a condition in which the stomach already empties abnormally slowly.
Why are side effects worse at the start?
The Zepbound label reports that the delay in gastric emptying is largest after the first dose and diminishes over time. The brainstem circuits involved in nausea are also thought to adapt with continued treatment. Together, that fits the trial pattern: symptoms cluster when treatment starts and when the dose goes up, then ease.
The timing is covered in detail in GLP-1 side effects by week.
From the makers of this guide
How Pep AI helps you see your own side-effect pattern
The label gives you population averages. What your prescriber needs is your version: which symptoms, how severe, and how they line up with your doses.
- 01
A side-effect tracker built for GLP-1s
Log symptoms grouped as injection site, digestive (nausea, bloating, constipation, diarrhea, sulfur burps, appetite changes), head and nerves, mood and energy, and body, each rated for severity.
- 02
Symptoms on the same timeline as doses
Every dose you log, shot or pill, sits on the same timeline as your symptoms, with reminders on your schedule, so patterns after a dose change are visible rather than remembered.
- 03
Food, protein and water against goals
Log meals by photo scan, barcode, restaurant menu scan, search, recents or quick-add, with protein, fiber and water tracked against goals and water reminders when appetite is low.
- 04
Pep Bot for label language
Ask Pep Bot what terms like eructation or dysesthesia mean. It explains concepts using a research-literature retrieval pipeline; it does not give dosing advice.
Which side effects usually fade, and which tend to linger?
Not every side effect behaves the same way. In the pooled semaglutide trials, nausea, diarrhea and vomiting peaked around the end of the dose-escalation period and declined afterward, and individual episodes were short. The Zepbound label says the same of its trials: most nausea, vomiting and diarrhea occurred during dose escalation and decreased over time. Other effects follow different rules, and any of the digestive ones can return briefly after a dose increase.
- Usually fade: nausea, diarrhea and vomiting. In the semaglutide trials, median episode lengths were 8, 3 and 2 days respectively.
- Often linger: constipation. Its median episode length in the same trials was 47 days (35 on placebo), far longer than the others.
- Tied to weight loss: hair loss. Both labels associate it with weight reduction, and both report it more often in women.
- Can signal something else: dizziness and fatigue. Both labels also report low blood pressure, some of it linked to fluid loss from digestive side effects, so dizziness deserves a look at your fluid intake.
- Specific to semaglutide's label: dysesthesia, meaning altered skin sensations such as tingling, burning or skin sensitivity, which the Wegovy label says became more common at higher doses.
Serious label warnings and the symptoms to act on
Everything here comes from the warnings and Medication Guides in the Wegovy and Zepbound labels. These events are uncommon, but they are why "it is probably just the medication" is not always the right assumption.
| Warning | What the label says | Symptoms to act on |
|---|---|---|
| Thyroid C-cell tumors (boxed warning) | Caused thyroid C-cell tumors in rodents; unknown whether it does in humans. Do not use with a personal or family history of medullary thyroid carcinoma (MTC) or with MEN 2. | A lump or swelling in the neck, hoarseness, trouble swallowing, or shortness of breath. Tell your provider. |
| Acute pancreatitis | Observed with GLP-1 medications, including fatal cases. The medication should be stopped if pancreatitis is suspected. | Severe stomach-area pain that will not go away, sometimes felt through to the back, with or without vomiting. Stop and call your provider right away. |
| Gallbladder disease | Gallstones and gallbladder inflammation occurred more often than on placebo. Rapid weight loss raises the risk, but it was higher even after accounting for that. | Pain in the upper stomach, fever, yellowing of the skin or eyes, or clay-colored stools. |
| Kidney injury from dehydration | Reports of acute kidney injury, some needing dialysis, mostly in people losing fluid through nausea, vomiting or diarrhea. | Nausea, vomiting or diarrhea that does not go away, or signs of dehydration. Tell your provider right away. |
| Severe stomach problems | Gastrointestinal reactions, sometimes severe. Not recommended in severe gastroparesis. | Stomach problems that are severe or will not go away. |
| Low blood sugar | Higher risk when combined with insulin or a sulfonylurea; the prescriber may need to lower those medicines. | Shakiness, sweating, dizziness, fast heartbeat, hunger, headache, blurred vision, confusion, irritability. |
| Serious allergic reactions | Anaphylaxis and angioedema have been reported. | Swelling of the face, lips, tongue or throat, trouble breathing or swallowing, severe rash or itching, fainting, very rapid heartbeat. Get emergency help. |
| Diabetic retinopathy complications (type 2 diabetes) | More retinopathy complications on semaglutide than placebo in a two-year trial (3% vs 1.8%). The Zepbound label notes temporary worsening with rapid improvement in blood sugar. | Any change in vision, if you have type 2 diabetes. |
| Faster resting heart rate (Wegovy label) | Resting heart rate rose on average, more in some people. | A racing or pounding heartbeat at rest that lasts several minutes. |
| Aspiration during anesthesia or sedation | Rare reports of stomach contents entering the lungs during procedures, despite following fasting instructions. | No symptom to wait for: tell every provider you take a GLP-1 before any surgery or sedated procedure. |
What happened to the warning about suicidal thoughts?
Earlier versions of the Wegovy, Zepbound and Saxenda labels told prescribers to monitor for depression and suicidal thoughts. On January 13, 2026, the FDA asked for that warning to be removed after its review of 91 clinical trials and a large insurance-claims study found no increased risk. The current Wegovy and Zepbound labels list the section as removed.
The FDA still advises telling your healthcare professional about new or worsening depression, suicidal thoughts, or any unusual changes in mood or behavior. If you are in distress, you can call or text 988 at any hour.
Who should not take these medications?
Both labels list two contraindications: a personal or family history of medullary thyroid carcinoma or MEN 2, and a previous serious allergic reaction to the drug or its ingredients. Neither is recommended in severe gastroparesis or alongside another GLP-1 medication. Both advise stopping for weight management once pregnancy is recognized, so anyone pregnant or planning a pregnancy should raise it with the prescriber early.
How to raise side effects with your prescriber
The labels leave the response to side effects with the prescriber. The Wegovy label, for example, gives prescribers the option of delaying a dose increase when a dose is not tolerated. That decision depends on details only you can supply, and a vague "I've been feeling sick" gives them little to work with. Never change, skip or split doses on your own.
- What the symptom is and how bad it gets, on a simple scale you use consistently.
- Which day after your injection it tends to start, and how long it lasts.
- Whether it began or worsened after a dose change or a missed dose.
- How much you are drinking, and whether you are urinating less than usual.
- Every other medicine you take, especially insulin, a sulfonylurea, or anything with a narrow safety margin.
Do GLP-1 medications affect other medicines?
They can, because slower stomach emptying can change how oral medicines are absorbed. Both labels call for extra monitoring of oral drugs that need tight control, and the Zepbound label names warfarin as an example. The Zepbound label also advises people using oral hormonal contraceptives to switch to a non-oral method, or add a barrier method, for 4 weeks after starting and for 4 weeks after each dose increase. Your pharmacist can check your full list.
Key takeaways
- Digestive side effects dominate: in the trials, 73% on Wegovy injection and 56% on Zepbound reported one, against 47% and 30% on placebo.
- Most were mild to moderate and clustered during dose increases; nausea, diarrhea and vomiting usually fade, while constipation lingers longer.
- Severe persistent stomach pain, gallbladder symptoms, fluid loss you cannot keep up with, and allergic swelling are not ordinary side effects. Act on them.
- The label warning about suicidal thoughts was removed in January 2026, but new or worsening mood changes should still be reported.
- Dose decisions belong to your prescriber. Your job is to bring specific, dated information about what happened.
Know which side effects are yours.
Pep AI puts your symptoms, doses, food and water on one timeline, so you and your prescriber can see what is actually happening. Download Pep AI on iPhone or Android.
Frequently asked questions
Keep reading
Sources
- Wegovy (semaglutide) prescribing information and Medication Guide, Novo Nordisk / FDA (revised 06/2026)
- Zepbound (tirzepatide) prescribing information and Medication Guide, Eli Lilly / FDA (revised 08/2026)
- FDA requests removal of suicidal behavior and ideation warning from GLP-1 receptor agonist medications, FDA Drug Safety Communication (January 13, 2026)
- Wharton S et al. Gastrointestinal tolerability of once-weekly semaglutide in adults with overweight or obesity, and the relationship between gastrointestinal adverse events and weight loss. Diabetes Obes Metab 2022
This guide is general information about GLP-1 medications, based on prescribing information and published research. It is not medical advice and does not replace your prescriber or pharmacist. If a symptom is severe, getting worse, or worrying you, contact your healthcare provider. In an emergency, call 911.
Published by the Pep AI team · Updated September 2026