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GLP-1 receptor agonist · safety

Semaglutide side effects

The semaglutide side effects reported most often are nausea, diarrhea and constipation. The full list is below, with the FDA label cited at the bottom of the page.

Rarer, but worth being able to spot: acute pancreatitis, gallbladder disease and hypoglycemia (with insulin or a sulfonylurea), and 3 more in the table below. Semaglutide also carries a boxed warning for risk of thyroid C-cell tumors.

These effects tend to cluster at the start and after each dose increase, and to settle down while the dose stays the same.

Semaglutide is the drug in Wegovy, Ozempic and Rybelsus. It copies a gut hormone called GLP-1, which helps control appetite and blood sugar. People take Wegovy for long-term weight management, and Ozempic or Rybelsus for type 2 diabetes.

All three products have FDA approval. Wegovy and Ozempic are weekly injections; Rybelsus is a daily tablet, and each has its own schedule.

Also sold as Wegovy and Ozempic and Rybelsus — one molecule, so these reactions apply to every brand of it.

Further down: the full list with frequencies · when to get medical help · questions

Medically reviewed by Jennifer Montecillo, MD · non-practicing medical reviewerReviewed 2026-08-20open the primary sources

At a glance

Common reactions listed

9

Serious reactions listed

6

Boxed warning

Yes

Strongest source

FDA label

The counts show how many distinct reactions the FDA label names. The percentages show how often a reaction appeared in a study group, not the chance that it will happen to you.

Boxed warning

Risk of thyroid C-cell tumors

Semaglutide caused thyroid C-cell tumors in rodents. It is not known if this happens in people. The label rules it out for anyone with a personal or family history of MTC or MEN 2.

Source: Wegovy (semaglutide) — FDA-approved Prescribing Information (DailyMed) · retrieved 2026-08-20

Common reactions

The full list, with the frequency band the FDA label gives for each one.

◆ Common reactionslabel frequency
ReactionFrequency
NauseaVery common (≥10%)
DiarrheaVery common (≥10%)
ConstipationVery common (≥10%)
VomitingVery common (≥10%)
Abdominal painCommon (1–10%)
HeadacheCommon (1–10%)
FatigueCommon (1–10%)
Dyspepsia (indigestion)Common (1–10%)
Injection-site reactionsCommon (1–10%)

Serious reactions to watch for

These are rarer, and they are the ones clinicians monitor for. Seek medical care if you have symptoms.

◆ Serious — monitorwarning/precaution
ReactionFrequency
Acute pancreatitisSerious — monitor
Gallbladder disease (cholelithiasis)Serious — monitor
Hypoglycemia (with insulin or a sulfonylurea)Serious — monitor
Acute kidney injury (from dehydration)Serious — monitor
Diabetic retinopathy complicationsSerious — monitor
Severe hypersensitivity reactionsSerious — monitor

FDA labelEvery reaction above comes from the product’s regulatory document. These are label facts, not personal advice.

When to seek medical care

Each one below is a serious reaction from the table above, written as the signs you would actually notice. Spotting them is the job of this section; working out what they mean is a clinician’s.

Acute pancreatitis

Urgent

Signs: Severe pain high in the abdomen that will not let up and may bore through to the back, often with nausea or vomiting that does not settle. People describe it as different from ordinary post-dose nausea, in that it does not come and go with meals.

The prescribing information lists this as a reaction that needs medical assessment. Call a clinician without waiting for the next appointment, or emergency services if the pain is severe.

Gallbladder disease

Prompt

Signs: Pain in the upper right side of the abdomen, sometimes after eating, with fever, yellowing of the skin or the whites of the eyes, unusually pale stools, or dark urine.

These are signs to get seen promptly rather than wait and watch.

Acute kidney injury from dehydration

Prompt

Signs: Vomiting or diarrhea bad enough that you cannot keep fluids down, passing much less urine than usual, dizziness when you stand up, or unusual weakness.

The label links the risk to dehydration, so ongoing fluid loss is worth reporting early. A clinician can check kidney function.

Severe hypersensitivity reaction

Urgent

Signs: Swelling of the face, lips, tongue or throat, trouble breathing or swallowing, a rash or hives spreading fast, or suddenly feeling faint.

This is the one on the list that does not wait. Call emergency services immediately rather than a clinic.

Hypoglycemia when combined with insulin or a sulfonylurea

Prompt

Signs: Shakiness, sweating, confusion, sudden hunger, a racing heart, blurred vision or trouble concentrating — especially in someone also taking insulin or a sulfonylurea.

The source ties this risk to that combination specifically, which makes your full medicine list worth going through with whoever prescribes for you. Severe confusion, a seizure or passing out is an emergency call.

Diabetic retinopathy complications

Prompt

Signs: New or fast-changing vision — blurring, floaters, dark patches, or losing part of the field of view — in someone who already has diabetic eye disease.

Vision changes get assessed by an eye specialist, and the source treats existing retinopathy as the context that matters. Report changes rather than waiting to see whether they settle.

EmergencySome symptoms should not wait for an appointment. Call emergency services (911 in the US) if they are severe, getting worse fast, or involve trouble breathing, chest pain, fainting or confusion.

3Read deeperTiming, evidence limits, and product context

When these effects tend to occur

GLP-1 labels and trial reports place stomach and gut effects most often at the start and after dose increases. A later increase can bring that early pattern back.

The same sources describe most of these effects as temporary — showing up after a step and easing off while the dose stays put. That is the pattern across whole trial populations. It is not a promise about you, and the sources do not commit to how long the easing takes.

The steps that matter

This is why approved schedules do not start at the full dose. The opening dose introduces the drug rather than treating the condition, and each step lasts for a minimum time before the next one is considered. The schedule is designed around how well people can handle each step as much as the dose itself. The semaglutide label schedule runs 0.25 mg → 0.5 mg → 1 mg → 1.7 mg → 2.4 mg, with each step held at least 4 weeks before the next is considered. Those changeovers are where the sources place the reactions.

See the full semaglutide titration schedule →

Making side effects easier to discuss

None of this is a recommendation, and none of it is treatment. These are the side-effect topics clinicians and drug labels tend to raise. They are written down here so your conversation with a prescriber starts further along than it otherwise would.

Meal size and pace
Portion size and how fast you eat are usually the first things raised when nausea tracks with meals. They come up because they are things you can describe precisely at your next appointment, which makes them useful information either way.
Fluids
Fluid intake comes up in almost every side-effect conversation. The reason is already on this page: where kidney injury appears in the serious list, dehydration is the route named. Vomiting and diarrhea are what lose fluid. That is why clinicians want to hear about them early rather than have you put up with them quietly.
Noticing patterns rather than guessing
Clinicians often suggest keeping track of what came before a bad day — the meal, the timing relative to the injection, how recently the dose changed. A specific account is worth more at an appointment than a vague one, and it is the part only the person taking the compound can supply.
How fast the dose moves
How quickly the dose goes up is a clinician’s call and belongs in that conversation, not on this page. Approved schedules set a minimum time at each step and treat the next step as conditional on the current one going well. Staying longer at a step is a recognized option, and the prescriber is the one who uses it.
Constipation as its own topic
Constipation usually gets discussed separately from nausea, because what helps is different and because anything reached for over the counter interacts with the rest of a medicine list. That makes it a question for a clinician or pharmacist rather than a search box.
Reporting rather than enduring
A side effect is information, not a test you failed. Clinicians want to hear about reactions early. They can hold a step, change the timing or look for another cause. The right choice depends on your symptoms, history and other medicines.

Starting, holding, changing, pausing or stopping a dose is a decision for the person who prescribes it.

Wegovy, Ozempic and Rybelsus side effects

Wegovy, Ozempic and Rybelsus are brand names for semaglutide. The frequency bands above describe the molecule. Percentages can still differ by brand because each label may be based on different trials, doses and groups of people.

The per-brand tables are published separately: Wegovy side effects in full and Ozempic side effects in full.

FDA has approved the branded pens, and the oral tablet Rybelsus.

FDA declared the semaglutide shortage resolved in February 2025. Mass compounding has wound down since. FDA has also proposed dropping it from the 503B bulks list.

Common questions

How long do semaglutide side effects last, and do they go away?

The sources do not commit to a set number of days. What they describe is a pattern — reactions cluster after you start and after each increase, then ease while the dose is held steady. Any page quoting an exact number of days is quoting something the sources do not say.

What are the most common semaglutide side effects?

Nausea, diarrhea, constipation and vomiting — the table above has the rest, each with its frequency band and source.

What is the semaglutide boxed warning?

Semaglutide carries a boxed warning for risk of thyroid C-cell tumors — the most serious warning a label can carry. Semaglutide caused thyroid C-cell tumors in rodents. It is not known if this happens in people. The label rules it out for anyone with a personal or family history of MTC or MEN 2.

Can the semaglutide dose be lowered if side effects are hard to tolerate?

That decision belongs to the prescribing clinician. The label schedule already sets a minimum time at each step and makes the next increase depend on how the current dose is going, so holding at a step is a recognized option inside the schedule.

Does semaglutide cause hair loss?

Hair loss is not among the reactions listed on this page for semaglutide, because the FDA label cited here does not carry it. Anything missing from the tables is outside what can be sourced here rather than ruled out, and a symptom that worries you belongs with a clinician.

Is fatigue a listed semaglutide side effect?

Yes — it is in the common reactions table above, with its frequency band. Being listed means it came up often enough in the trial population to reach the FDA label; it does not establish the cause in any one case.

Is constipation a listed semaglutide side effect?

Yes — it appears on this page among the reactions reported in the FDA label. It usually gets discussed separately from nausea, partly because anything reached for over the counter interacts with the rest of a medicine list.

What should someone do about a serious semaglutide reaction?

Contact a clinician promptly, and emergency services if symptoms are severe or getting worse quickly. The section above describes what those reactions actually look like, so they can be spotted early rather than explained away.

Do the frequencies on this page mean the chance it happens to one person?

No. These figures describe groups in a study. A band shows how often a reaction appeared under that trial’s conditions. It cannot predict what will happen to one person.

Related

The schedule these reactions were recorded against, the comparisons, and the sourcing rules behind every grade on this page.

The labeled semaglutide escalation, from first step to maintenance

Published semaglutide dose information, not a personal schedule to follow.

How strong the evidence is for semaglutide

The strongest source for semaglutide is an approved label.

The semaglutide half of tirzepatide vs semaglutide

Each page in tirzepatide vs semaglutide on its own terms, rather than folded into semaglutide.

Wegovy vs zepbound, with the semaglutide page in full

Approved uses, populations, schedules and devices, apart from semaglutide.

Convert a semaglutide amount to units on a U-100 barrel

Every step of the semaglutide arithmetic is printed, so the result can be checked by hand.

Semaglutide, then the page behind FDA’s GLP-1 mental-health finding

A class-level safety finding kept separate from individual symptoms and claims that a drug works. alongside semaglutide.

From semaglutide to the alcohol evidence, with the outcomes kept separate

A three-study ledger separated from personal drinking limits and treatment advice. alongside semaglutide.

The Ozempic trial tables behind the semaglutide page

5 rows at the Ozempic label’s own cut-off, not at a semaglutide threshold.

Questions readers ask

How long to lose 30 pounds on semaglutide?

Nothing published pins it to a specific week. SURMOUNT-5 reports an average 13.7% reduction in body weight after 72 weeks.

A percentage only becomes pounds once you know the starting weight, and an average only describes the group rather than the person reading it.

What are the dangers of taking semaglutide?

The label names them itself. Pancreatitis, gallbladder disease and kidney injury after fluid loss are three. The others are low blood sugar alongside insulin, worsening diabetic eye disease, and severe allergic reactions.

Above all of those sits the boxed warning about thyroid C-cell tumors in rodents. The label says it is unknown whether the same happens in people, which is a narrower statement than either side of the argument usually makes.

When are the worst side effects of semaglutide?

Nobody has published a timeline. The label counts how many people reported an effect at all across a trial, not which week they reported it in.

The one structural clue is the ladder itself. The label steps the dose every four weeks rather than starting at the top. That schedule exists because the drug is harder to take at a dose reached too quickly.

Are there long-term side effects from semaglutide?

The longest published windows in this repo are the trials themselves — up to 68 weeks on the Wegovy label, 72 weeks in SURMOUNT-5. Beyond that, nothing here reports what happens over years.

That is missing evidence, not proof of safety. FDA continues collecting reports after approval, but report counts are not incidence rates.

1primary source, each with the day we read it — open the documents used on this page