GLP-1 explainers

GLP-1 Side Effects: What Is Common, What Is Serious

5 min read · updated October 9, 2026

The brief

The most common side effects are nausea, diarrhea, vomiting and constipation.¹
Starting low and increasing the dose gradually is meant to reduce them.¹
Serious risks include pancreatitis, gallbladder disease and kidney problems from dehydration.¹
Severe stomach pain that does not go away needs urgent medical attention.¹

Most people who stop a GLP-1 early do it because of side effects. Knowing what to expect helps.

The common ones

Stomach and digestive effects lead the list: nausea, diarrhea, vomiting, constipation, indigestion and stomach pain.^1,2 They are most noticeable when starting or after a dose increase, which is why doses are raised gradually.¹

Practical steps people use

Eating smaller meals and stopping at the first sense of fullness.
Avoiding very fatty or greasy food.
Drinking enough fluids, especially with vomiting or diarrhea.²

If side effects are hard to tolerate, the prescribing clinician can slow the dose increase.

The serious ones

The tirzepatide label lists less common but serious risks:¹

Pancreatitis: severe stomach pain that may spread to the back, with or without vomiting.
Gallbladder problems, including gallstones.
Kidney problems, usually from dehydration caused by vomiting or diarrhea.
Low blood sugar, mainly when combined with insulin or sulfonylureas.
Serious allergic reactions.
Thyroid C-cell tumors: seen in rodents; the boxed warning says not to use it with a personal or family history of medullary thyroid carcinoma or MEN 2.

Birth control and pregnancy

The label notes tirzepatide can make oral contraceptives less effective for a period after starting and after each dose increase, and it should not be used during pregnancy.¹

Compounded versions

The FDA has received reports of adverse events, some linked to dosing errors, with compounded GLP-1 drugs.³ Follow the dosing instructions from your prescriber and pharmacy exactly.

Bottom line. The most common side effects are nausea, diarrhea, vomiting and constipation.¹

Talk to a clinician. This article explains the evidence; it cannot tell you what is right for you. A licensed clinician who knows your health history and medications can.

Important safety information. The FDA label for tirzepatide carries a boxed warning about thyroid C-cell tumors seen in rodents; it should not be used by anyone with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2.¹ The most common side effects are nausea, diarrhea, vomiting and constipation.¹ Serious risks include pancreatitis, gallbladder problems and low blood sugar when combined with insulin or sulfonylureas.¹ Compounded versions are not FDA-approved.³ Only a licensed clinician should decide whether it is appropriate for you.

Quick questions

What are the most common GLP-1 side effects?

Nausea, diarrhea, vomiting and constipation are the most common, especially when starting or increasing the dose.

When should I call a doctor on a GLP-1?

Severe stomach pain that does not go away, signs of an allergic reaction, or vomiting and diarrhea that cause dehydration need prompt medical attention.

More briefs

Sources

Tirzepatide prescribing information. DailyMed, U.S. National Library of Medicine.
Tirzepatide injection. MedlinePlus Drug Information, U.S. National Library of Medicine.
U.S. Food and Drug Administration. FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss.