Semaglutide Side Effects: What to Expect and When to Get Help (2026)

If you are thinking about a GLP-1 medication, semaglutide side effects are probably near the top of your list of questions. Most reported effects involve the digestive system, tend to show up early, and often ease with time, but a few are serious and need prompt care. This guide walks through what the clinical trials found, how long symptoms usually last, and when to call your provider or 911.

Key takeaways

• In the Wegovy® clinical trials, nausea was the most common side effect, reported by 44% of adults on the medication versus 16% on placebo.
• Digestive side effects were reported most often while the dose was being increased, and in STEP 1 they typically subsided with time, though experiences vary.
• Semaglutide carries a boxed warning about thyroid C-cell tumors seen in rodents and is not for people with a personal or family history of medullary thyroid carcinoma or MEN 2.
• Severe abdominal pain, an allergic reaction, vision changes or suicidal thoughts need same-day care; call 911 in any emergency.
• Compounded semaglutide is not FDA-approved, and the FDA has received reports of adverse events that may be related to dosing errors with compounded products.

The most common semaglutide side effects

Semaglutide is the active ingredient in Wegovy®, which is indicated for chronic weight management, and Ozempic®, which is indicated for type 2 diabetes. It mimics GLP-1, a gut hormone that slows stomach emptying and signals fullness to the brain. That same action explains why most side effects involve the stomach and intestines. Brand names are trademarks of their respective owners; Forever Health Rx is not affiliated with them.

The table below lists selected adverse reactions from the Wegovy® prescribing information for adults in the 68-week trials, where they occurred more often than with placebo. These are trial frequencies, not predictions for any one person. Individual results vary.

In STEP 1, nausea and diarrhea were typically transient and mild to moderate. Across the Wegovy® weight-management trials, about 7% of adults on the medication stopped because of a side effect, compared with about 3% on placebo, and nausea, vomiting and diarrhea were the most common reasons.

Semaglutide fatigue

Fatigue (including weakness) was reported by 11% of participants on Wegovy® versus 5% on placebo. If tiredness is persistent or gets in the way of daily life, tell your provider, who may check for causes such as dehydration from nausea or diarrhea, or low blood sugar in people who also take diabetes medications.

When do semaglutide side effects start, and how long do they last?

In the trials, the dose was raised gradually over several months, and the Wegovy® label notes that digestive side effects were reported most frequently during that dose-escalation period.

There is no fixed timeline. In STEP 1, nausea and diarrhea were typically transient and subsided with time. If your symptoms linger, that is worth discussing with your provider rather than pushing through.

If you stop semaglutide, the medication does not leave the body right away. Its elimination half-life is about 1 week, and the label says it stays in the circulation for about 5 to 7 weeks after the last dose.

Practical ways to manage semaglutide side effects

A handful of simple strategies can make the early weeks more comfortable. None of these replace medical advice, and you should never change your own dose.

• Eat smaller meals, and stop when you feel full. Slower stomach emptying means a normal-sized plate can feel like too much.
• Go easy on greasy, fried or very sweet foods. Some people find these harder to tolerate.
• Stay hydrated. Nausea, vomiting and diarrhea all pull fluid from the body, and the label notes that most reported cases of kidney injury happened in people who became dehydrated this way.
• Pair fiber with water. For constipation, more fiber without more fluid can make things worse. Light daily activity helps too.

Dose changes belong to the provider. The Wegovy® label lets a prescriber consider delaying a dose increase when a patient is not tolerating the current level. Your job is to report honestly how you feel; theirs is to decide what to do with that information.

Serious side effects and warnings

The Wegovy® label lists the warnings below. Rare does not mean impossible, so read the full Important Safety Information before your online visit and again when you start.

Thyroid C-cell tumors (boxed warning)

Semaglutide caused thyroid C-cell tumors in rodents. It is unknown whether this happens in humans, so semaglutide is contraindicated in anyone with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2). Report any lump or swelling in the neck, trouble swallowing, hoarseness or shortness of breath.

Pancreatitis

Acute pancreatitis has been reported. The warning sign is severe, persistent abdominal pain that may radiate to the back, with or without nausea or vomiting. The Medication Guide says to stop the medication and call your provider right away if that happens.

Gallbladder problems

In the trials, gallstones were reported in 1.6% of adults on Wegovy® injection versus 0.7% on placebo. Substantial or rapid weight loss can raise gallstone risk, although the label notes gallbladder problems were more common with Wegovy® even after accounting for weight loss. Pain in the upper stomach, fever, yellowing of the skin or eyes, or clay-colored stools should prompt a call to your provider.

Kidney injury from dehydration

Vomiting and diarrhea can lead to dehydration, and dehydration can injure the kidneys; in the trials, the risk was higher in people with a history of kidney problems. Keeping fluids up during rough patches helps, and your provider may check your kidney function if you have these symptoms.

Low blood sugar (hypoglycemia)

Low blood sugar has been reported with GLP-1 medications in people without diabetes, but the risk is higher when semaglutide is combined with insulin or a sulfonylurea, and the label advises that those medications may need adjustment. Shakiness, sweating, confusion or a racing heart are signs to act on.

Diabetic retinopathy complications

In people with type 2 diabetes, a rapid improvement in blood sugar has been linked to temporary worsening of diabetic retinopathy. Anyone with a history of retinopathy should be monitored, and any change in vision deserves a prompt exam.

Mood changes and suicidal thoughts

Earlier versions of the label carried a warning about suicidal thoughts and behavior. In January 2026, the FDA said its evaluation did not identify an increased risk with GLP-1 medications and asked for the warning to be removed, and it was taken off the Wegovy® label in February 2026. The FDA still advises telling your health care professional about new or worsening depression, suicidal thoughts or unusual changes in mood. If you have thoughts of harming yourself, get help right away.

Ileus and aspiration with anesthesia

Ileus, a condition in which the intestines stop moving, has been reported since GLP-1 medications reached the market, along with rare aspiration during general anesthesia or deep sedation because of slowed stomach emptying. Tell every surgeon, anesthesiologist and dentist that you take a GLP-1 medication.

Allergic reactions and heart rate

Serious allergic reactions, including anaphylaxis and angioedema (swelling of the face, lips, tongue or throat), have been reported. Trial participants also had a small average increase in resting heart rate, so report a heart that races or pounds while you are at rest.

When to call your provider vs. 911

Call 911 or go to the nearest emergency room for trouble breathing, swelling of the face or throat, chest pain, fainting, signs of a severe allergic reaction, or any thoughts of harming yourself. You can also call or text the 988 Lifeline at 988.

Contact your provider the same day for severe or persistent abdominal pain, repeated vomiting that keeps you from holding down fluids, signs of dehydration such as dizziness or very dark urine, symptoms of low blood sugar, upper stomach pain with fever or yellowing skin, a lump in the neck, or any change in vision.

Message your provider at your next opportunity for nausea, constipation, fatigue or hair shedding that is bothersome but manageable. These everyday issues are easier to address early.

Does semaglutide cause hair loss?

Hair loss appears in the Wegovy® label, reported by 3% of adults on the medication versus 1% on placebo. The label does not describe how long it lasts or what causes it.

If you notice shedding, tell your provider. They may check iron, thyroid function and protein intake, and can advise on whether anything about your plan should change. Our guide on protein on GLP-1 covers eating enough protein.

Long-term side effects of semaglutide: what the evidence says

The largest long-term safety dataset is the SELECT trial, published in the New England Journal of Medicine in 2023. It followed 17,604 adults aged 45 or older with overweight or obesity and cardiovascular disease, but without diabetes, for an average of about 3.3 years (39.8 months). Major adverse cardiovascular events occurred in 6.5% of participants on semaglutide versus 8.0% on placebo. Stopping because of adverse events was more common on semaglutide (16.6% versus 8.2%).

Semaglutide has also been approved for type 2 diabetes as Ozempic® since 2017, which adds years of post-marketing monitoring. The Wegovy® label notes that semaglutide lowers body weight with greater fat mass loss than lean mass loss; data on use over a decade or more are still limited. In an extension of the STEP 1 trial, participants regained about two-thirds of their prior weight loss in the year after stopping treatment, which is why providers frame this as ongoing care. These are study averages; individual results vary.

For how this evidence compares with the newer dual-action option, read the pillar guide on semaglutide vs. tirzepatide or the companion article on whether tirzepatide is safe.

Compounded semaglutide and side effects

Compounded semaglutide is not FDA-approved. The FDA does not review compounded medications for safety, effectiveness or quality, and they are not the same as the FDA-approved products Wegovy® and Ozempic®. They are not generic versions of those products either.

The FDA has said it has received reports of adverse events, some requiring hospitalization, that may be related to dosing errors with compounded injectable semaglutide, including patients measuring and self-administering incorrect doses. The FDA determined the national semaglutide shortage resolved in February 2025.

If a compounded product is ever part of your care, ask which licensed pharmacy makes it and how the dose is measured. The guide on how to spot a legitimate online GLP-1 provider lists the questions worth asking.

How to report semaglutide side effects

Report side effects in two places. First, message your provider through the patient portal so your plan can be adjusted; clinical messages are typically answered within . Second, you can report to the FDA's MedWatch program at 1-800-FDA-1088 or online at www.fda.gov/medwatch.

A licensed provider can review your health history in an online visit. Read the semaglutide program page and its Important Safety Information, check am I a candidate for GLP-1?, then start your health assessment when you are ready. Submitting a visit does not guarantee a prescription; the provider decides.