GLP-1 Side Effects: A Plain-Language Guide From the Labels

Short answer: In the clinical trials behind the Wegovy® (semaglutide) and Zepbound® (tirzepatide) labels, the most common side effects were stomach and bowel related: nausea, diarrhea, vomiting, constipation and abdominal pain. The labels also carry warnings about thyroid tumors seen in rodents, pancreatitis, gallbladder disease, kidney injury from dehydration and more. This page summarizes what the labels say. It is not a substitute for your prescriber.

What are the most common GLP-1 side effects?

MedlinePlus, the NIH patient-information site, lists these semaglutide side effects to report if they are “severe or do not go away”: nausea, vomiting, diarrhea, stomach pain, constipation, heartburn, burping, runny nose or sore throat, and headache. Semaglutide is the active ingredient in Wegovy and Ozempic®.

How often did side effects happen in trials?

The labels report the share of trial participants who had each reaction. The numbers below are the labels’ own, from weight-reduction trials. They come from different trials with different designs, so they should not be compared head to head.

Wegovy 2.4 mg vs placebo (label Section 6.1, reactions in at least 2% of Wegovy-treated adults and more often than placebo):

Reaction	Placebo (N=1,261)	Wegovy (N=2,116)
Nausea	16%	44%
Diarrhea	16%	30%
Vomiting	6%	24%
Constipation	11%	24%
Abdominal pain	10%	20%
Headache	10%	14%
Fatigue	5%	11%

Zepbound vs placebo (label Section 6.1, pooled weight-reduction trials):

Reaction	Placebo (N=958)	5 mg (N=630)	10 mg (N=948)	15 mg (N=941)
Nausea	8%	25%	29%	28%
Diarrhea	8%	19%	21%	23%
Vomiting	2%	8%	11%	13%
Constipation	5%	17%	14%	11%
Abdominal pain	5%	9%	9%	10%
Dyspepsia (indigestion)	4%	9%	9%	10%

The strengths shown are the ones studied in the trial; your prescriber chooses what fits you.

What serious warnings do the labels list?

Both labels open with a boxed warning about thyroid C-cell tumors. The Wegovy label says: “In rodents, semaglutide causes dose-dependent and treatment-duration-dependent thyroid C-cell tumors.” The Zepbound label says the same about tirzepatide in rats and states that the medicine is contraindicated in people with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).

The Warnings and Precautions sections of the two labels include:

• Acute pancreatitis
• Acute gallbladder disease
• Acute kidney injury due to volume depletion (dehydration)
• Severe gastrointestinal adverse reactions
• Hypersensitivity (allergic) reactions
• Hypoglycemia, with Wegovy’s label also noting it in people with type 2 diabetes
• Diabetic retinopathy complications in people with type 2 diabetes
• Pulmonary aspiration during general anesthesia or deep sedation

Wegovy’s label additionally lists an increase in heart rate. Read the full label for the details and who is affected.

Are injection site reactions a side effect too?

Yes, but they are local. See how the labels describe injection sites and rotation.

How can you keep a record of how you feel?

Some people note symptoms next to each shot so they can show the pattern at their next appointment. Weeko, a shot tracker coming to iPhone and Android, is being built around that kind of simple log. It is a logbook, not medical guidance.

When to call your doctor

MedlinePlus says to call your doctor immediately or get emergency medical treatment for any of these:

• Ongoing pain that begins in the upper left or middle of the stomach and may spread to the back, with or without vomiting
• Rash, itching, fainting or dizziness, or swelling of the eyes, face, mouth, tongue or throat
• Difficulty breathing or swallowing
• Decreased urination, or swelling of the legs, ankles or feet
• Vision changes
• Pain in the upper stomach, yellowing of the skin or eyes, fever or clay-colored stools
• A rapid or pounding heartbeat
• A lump or swelling in the neck, or hoarseness

Also tell your doctor if you have had diarrhea, nausea or vomiting, or if you cannot drink liquids by mouth, because that can lead to dehydration. For anything else that is severe or does not go away, ask your prescriber or pharmacist.