Safety guide

What are the side effects of semaglutide?

8 min read Updated August 2026 US-licensed providers

The short answer

Most semaglutide side effects are gastrointestinal. Nausea, vomiting, diarrhea, and constipation are the ones reported most often, and they cluster around starting treatment and each dose increase. Less common but serious risks include pancreatitis and gallbladder disease. The brand labels carry a boxed warning for thyroid C-cell tumors, and semaglutide is contraindicated if you or a close relative has had medullary thyroid carcinoma or MEN 2.

Which semaglutide side effects are most common?

The FDA prescribing information for Wegovy (semaglutide) lists the reactions reported most often in its trials, and the pattern is consistent: the digestive system takes the brunt of it. Ordered roughly from most to least frequently reported:

Side effect	How often it is reported	What it usually looks like
Nausea	Most commonly reported	Strongest in the days after a dose increase, often easing as your body adjusts
Diarrhea	Commonly reported	Loose stools, often intermittent rather than constant
Vomiting	Commonly reported	Usually tied to large, rich, or fast-eaten meals
Constipation	Commonly reported	Frequently linked to eating and drinking less overall
Abdominal pain, bloating, burping, reflux, indigestion	Commonly reported	The stomach empties more slowly, so food sits longer
Headache, fatigue, dizziness	Commonly reported	Often related to eating and drinking less rather than the drug itself
Pancreatitis, gallbladder disease, acute kidney injury, allergic reactions	Less common, potentially serious	Need prompt medical attention, not waiting it out
Thyroid C-cell tumors	Boxed warning	Seen in rodents; whether semaglutide causes these tumors in humans is not known

Grouped from the FDA prescribing information for Wegovy (semaglutide). Labeling is updated over time, so check the current prescribing information. Rates are not listed here; frequency figures and trial data live on our science pages.

Most people who stop treatment early do so because of the digestive symptoms, not the rare risks, which is why the practical management on how to reduce GLP-1 side effects matters as much as the safety list.

Why side effects cluster around dose increases

Semaglutide slows how quickly your stomach empties and acts on the appetite signalling that tells your brain you have eaten enough. Both effects are strongest when the amount of medication in your system changes, which is exactly what happens in the week or two after you step up a dose.

That is the whole reason the schedule starts low and climbs slowly. The starting dose on the label is not a treatment dose, it is a tolerability dose. See the semaglutide titration schedule for the week-by-week pattern and what your provider can change if a step is too much.

If a dose increase is not tolerable, the label supports staying at the current dose for longer rather than pushing through. That is a conversation with your provider, not a decision to make alone.

How side effects are managed with a provider

Side effects are a dosing and monitoring problem, which is why treatment through a clinic with real follow-up is different from a vial in the mail. At Expert Health, compounded semaglutide starts at $199 per month ($597 for a 3-month supply), and the plan is built around the follow-up:

A free consultation with a health specialist, with no obligation to buy
A US-licensed provider reviews your history, including any thyroid or pancreatic history, before anything is prescribed
Semaglutide compounded by an FDA-regulated US pharmacy and shipped free and discreetly
Provider check-ins every four weeks, so a dose that is not sitting well can be held or adjusted rather than endured

Compounded medications are not FDA-approved, meaning the FDA has not reviewed them for safety, effectiveness, or quality before they are dispensed. A US-licensed provider decides whether treatment is appropriate for you.

Semaglutide, as low as $199/mo Prescribed by a US-licensed provider, compounded by a licensed US pharmacy, shipped free. See the full plan and what is included.

See Semaglutide

The serious risks you should know about

These are much less common than the digestive symptoms, but they are the reason semaglutide is a prescription medication with monitoring attached. The FDA label for Wegovy lists, among its warnings and precautions:

Acute pancreatitis. Inflammation of the pancreas has occurred in trials. The label directs that treatment be stopped promptly if pancreatitis is suspected. Severe, persistent abdominal pain, sometimes spreading to the back and sometimes with vomiting, is the classic warning sign.
Acute gallbladder disease. Gallstones and gallbladder inflammation have occurred. Rapid weight loss of any kind raises gallstone risk, so this is not unique to the medication.
Acute kidney injury. Usually a downstream effect of dehydration from severe nausea, vomiting, or diarrhea, which is why fluids matter so much.
Hypoglycemia. Low blood sugar risk rises if semaglutide is combined with insulin or a sulfonylurea. Your provider adjusts those medications, you do not.
Serious allergic reactions. Anaphylaxis and angioedema have been reported after marketing. Any swelling of the face, lips, or throat, or trouble breathing, is an emergency.
Diabetic retinopathy complications in people with type 2 diabetes, and an increase in resting heart rate, both of which the label says to monitor.
Mood changes. The label directs providers to monitor for depression or suicidal thoughts and to stop treatment if they develop.

One practical item that is easy to miss: because semaglutide delays stomach emptying, tell your surgical and anesthesia team that you are taking it before any procedure involving sedation, and tell any prescriber, because the absorption of oral medications you swallow can be affected.

The thyroid boxed warning, and who should not take semaglutide

Semaglutide brand labels carry a boxed warning, the FDA's strongest warning format, for the risk of thyroid C-cell tumors. In rodent studies, semaglutide caused thyroid C-cell tumors. It is not known whether semaglutide causes these tumors, including medullary thyroid carcinoma (MTC), in humans. The honest statement is that the rodent finding is real and the human relevance is unresolved, and the label handles that by ruling out the people most at risk.

Tell your provider before starting if you have

Any history of pancreatitis or gallbladder disease
Type 2 diabetes, especially if you take insulin or a sulfonylurea
A history of diabetic retinopathy
Kidney disease, or any condition that makes dehydration risky
A history of depression or suicidal thoughts
Severe gastrointestinal disease, including gastroparesis
A plan to become pregnant, since the label says to stop at least 2 months before a planned pregnancy

Semaglutide is contraindicated if you have

A personal history of medullary thyroid carcinoma (MTC)
A family history of medullary thyroid carcinoma
Multiple Endocrine Neoplasia syndrome type 2 (MEN 2)
A known hypersensitivity to semaglutide or any ingredient in the product
A current pregnancy, since the label says to discontinue when pregnancy is recognized

These are the contraindications on the brand label. A provider screens for them and will decline to prescribe if semaglutide is not appropriate for you. See also who qualifies for a GLP-1.

When to call your provider instead of waiting it out

Ordinary nausea in the days after a dose step is expected and usually settles. These are not that, and none of them are worth being stoic about:

Severe or persistent abdominal pain, particularly if it spreads to your back, with or without vomiting.
Vomiting or diarrhea that stops you keeping fluids down for a day, or any signs of dehydration such as dark urine, dizziness on standing, or barely urinating.
Pain in the upper right abdomen, fever, or yellowing of the skin or eyes.
Swelling of the face, lips, tongue, or throat, or any trouble breathing. That is emergency care, not a phone call.
A lump in the neck, difficulty swallowing, persistent hoarseness, or shortness of breath.
New or worsening depression, or any thoughts of self-harm.
Symptoms that are not improving after a couple of weeks at a stable dose, or that get worse rather than better.

For the day-to-day tactics, meal size, food choices, hydration, and titration pace, see how to reduce GLP-1 side effects. For the same rundown on the other molecule, see tirzepatide side effects.

Frequently asked questions

What are the most common side effects of semaglutide?

Nausea, diarrhea, vomiting, and constipation are the most commonly reported, along with abdominal pain, bloating, burping, reflux, indigestion, headache, fatigue, and dizziness. They are usually worst in the days after starting and after each dose increase. This is drawn from the FDA prescribing information for Wegovy.

How long do semaglutide side effects last?

For most people the digestive symptoms are worst in the first days after a dose increase and ease as the body adjusts to that dose. If symptoms are not settling after a couple of weeks at a stable dose, or are getting worse, contact your provider rather than pushing through. Your provider can hold the dose or slow the schedule.

Does semaglutide cause thyroid cancer?

It is not known. In rodent studies semaglutide caused thyroid C-cell tumors, which is why the brand labels carry a boxed warning, but whether it causes them in humans has not been determined. Semaglutide is contraindicated if you have a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2.

Can semaglutide cause pancreatitis or gallbladder problems?

Both are listed in the warnings on the FDA label and both have occurred in clinical trials. Severe, persistent abdominal pain that may spread to the back is the classic sign of pancreatitis and needs prompt medical attention. Rapid weight loss of any kind also raises the risk of gallstones.

Does semaglutide cause hair loss?

Hair loss is not listed among the most common adverse reactions on the Wegovy label, but some people do report thinning during weight loss. Shedding after rapid weight loss or a period of low intake is a recognized pattern that is generally temporary. Adequate protein and overall nutrition are worth discussing with your provider.

What is 'Ozempic face', and is it a side effect?

It is a nickname for the hollowed or aged look some people notice in the face after losing a lot of weight. It reflects loss of facial fat that comes with weight loss generally, not a specific toxicity of the medication. A slower rate of loss and attention to nutrition are the usual levers, and it is worth raising with your provider.

Does semaglutide affect mood?

The FDA label directs providers to monitor patients for depression or suicidal thoughts and to stop treatment if they develop. If your mood changes on treatment, tell your provider promptly rather than waiting for the next check-in. Any thoughts of self-harm need urgent help.

Is compounded semaglutide safer or riskier than the brand?

Compounded semaglutide is not FDA-approved, meaning the FDA has not reviewed it for safety, effectiveness, or quality before it is dispensed, and the brand safety information is what its risks are described from. A US-licensed provider weighs the risks and benefits with you and prescribes only if it is appropriate.

Sources

Wegovy (semaglutide) injection, Prescribing Information · U.S. Food and Drug Administration
Ozempic (semaglutide) injection, Prescribing Information · U.S. Food and Drug Administration

This article is for general educational purposes and is not medical or legal advice. Statements have not been evaluated by the FDA, and treatments referenced are not intended to diagnose, treat, cure, or prevent any disease. Compounded medications are not FDA-approved. Individual results vary. Always consult a licensed provider before starting any treatment.