Semaglutide Side Effects: What Is Common, What Is Rare and When to Call Your Doctor

Semaglutide is the active ingredient in Wegovy, which is prescribed for weight management, and in Ozempic, which is prescribed for type 2 diabetes. It is one of the most studied weight-loss medicines ever, which means we know a lot about its side effects: which ones are common, when they tend to show up, which ones are rare but serious, and what the warning signs look like.

This guide walks through all of it using the official FDA prescribing information and the published trial data, in plain English. It is not a substitute for advice from your own prescriber, who knows your history and your other medicines.

The short answer

Most semaglutide side effects are digestive, and most are temporary. In the three main Wegovy weight-loss trials, which included 2,116 adults on the 2.4 mg weekly injection and 1,261 on placebo for up to 68 weeks:

• Nausea affected 44% of people on semaglutide versus 16% on placebo.
• Diarrhea affected 30% versus 16%.
• Vomiting affected 24% versus 6%.
• Constipation affected 24% versus 11%.

A pooled analysis of those trials found that 99.5% of these digestive events were non-serious and 98.1% were mild to moderate. They came and went and happened most often during or soon after a dose increase. About 4.3% of people on semaglutide stopped treatment permanently because of digestive side effects.

Serious side effects such as pancreatitis, gallbladder disease and kidney problems from dehydration are uncommon, but they are real, and knowing the warning signs is the most useful thing you can take away from this article.

Semaglutide at a glance

Semaglutide copies the action of GLP-1, a hormone your gut releases after eating. It slows the emptying of your stomach, helps your body release insulin when blood sugar rises and acts on appetite centers in the brain so you feel full sooner and think about food less. For a fuller explanation, see What Is Semaglutide? and how GLP-1s work for weight loss.

Those same effects explain most of its side effects. A slower stomach can mean nausea, fullness, burping and reflux. Changes in how food moves through the gut can mean diarrhea or constipation. Eating much less can contribute to tiredness, dizziness and, over months, hair shedding.

Wegovy now comes in several forms. The current US label covers a weekly injection at a 2.4 mg maintenance dose, a higher 7.2 mg weekly injection, and a 25 mg daily tablet. Ozempic contains the same molecule and is used for diabetes; our comparison of Wegovy vs Ozempic explains how the two differ. The figures in this article come mainly from the Wegovy label because it covers weight-loss use.

The most common side effects, by the numbers

The table below lists every side effect that the Wegovy label reports in at least 2% of adults on the 2.4 mg injection and more often than on placebo, in the weight-loss trials.

Side effect	Semaglutide 2.4 mg	Placebo
Nausea	44%	16%
Diarrhea	30%	16%
Vomiting	24%	6%
Constipation	24%	11%
Stomach (abdominal) pain	20%	10%
Headache	14%	10%
Fatigue	11%	5%
Indigestion (dyspepsia)	9%	3%
Dizziness	8%	4%
Bloating (abdominal distension)	7%	5%
Burping (eructation)	7%	under 1%
Gas (flatulence)	6%	4%
Stomach flu (gastroenteritis)	6%	4%
Reflux (GERD)	5%	3%
Gastritis	4%	1%
Hair loss	3%	1%
Altered skin sensation (dysesthesia)	2%	1%

Source: Wegovy prescribing information, Table 3. Low blood sugar (6% versus 2%) was also reported in the trial of people with type 2 diabetes.

Two things stand out. First, the placebo column is not zero. Many people on placebo also reported nausea, diarrhea and headaches, which is a reminder that some symptoms would have happened anyway. Second, the gap between semaglutide and placebo is largest for nausea and vomiting, which are the side effects most directly tied to the slowing of the stomach.

When side effects happen, and how long they last

The timing of semaglutide side effects follows a clear pattern. Treatment starts at a low dose and is stepped up over several months to reach the maintenance dose. The Wegovy label says digestive reactions were reported most often during this dose escalation, and the pooled STEP analysis found they were mostly transient.

In practice, that means many people notice nausea or fullness in the first days after starting or after each step up, and then feel better as their body adjusts. Once people reach a stable dose, digestive side effects tend to become less frequent. In the STEP 4 trial, which looked at people who had already tolerated 20 weeks of semaglutide, the maintenance dose was described as well tolerated.

Not everyone follows this pattern. Some people have very few side effects, and some have symptoms that linger. If you are struggling, the right move is to talk with your prescriber. Dose schedules are set by your prescriber, and clinicians sometimes stay longer at a lower dose when side effects are hard to tolerate. An obesity medicine physician on YouTube summed up the approach she uses with patients as “start low and go slow”, and said it is fine to ask your prescriber whether you can stay at a dose a little longer. That is a conversation to have with your own clinician, not a change to make on your own.

Side effects are not what drives the weight loss

A common belief is that semaglutide works because it makes people feel sick. The data do not support that. In the pooled STEP 1 to 3 analysis, people who never had digestive side effects lost a similar amount of weight to people who did, and less than 1 percentage point of the extra weight loss compared with placebo was explained by those side effects. Most of the effect comes from changes in appetite and fullness, not from nausea.

What changes at the higher 7.2 mg dose

The 2026 Wegovy label includes a higher 7.2 mg weekly injection, studied in two 72-week trials with 1,311 people on 7.2 mg, 304 on 2.4 mg and 303 on placebo. Here is how the most common side effects compared.

Side effect	7.2 mg	2.4 mg	Placebo
Nausea	39%	35%	13%
Vomiting	22%	16%	6%
Altered skin sensation (dysesthesia)	22%	6%	0%
Constipation	20%	19%	8%
Stomach pain	12%	9%	7%
Fatigue	11%	9%	5%
Headache	9%	8%	7%
Dizziness	6%	5%	1%
Hair loss	6%	3%	1%

Source: Wegovy prescribing information, Table 4.

The standout is dysesthesia, a catch-all term for altered skin sensations such as tingling, burning, skin sensitivity or skin that feels painful to the touch. The label says it became more common as the dose and drug levels in the blood went up. Among people who had it on 7.2 mg, most recovered when their clinician lowered the dose or paused treatment, although 18% had not recovered by the end of the trial, mostly people whose dose was left unchanged. About 5% of people on either 7.2 mg or 2.4 mg stopped treatment because of side effects, versus 2% on placebo.

Other side effects worth knowing about

Beyond the top of the list, the label describes several less common effects that people often ask about.

• Hair loss. The label links it to weight reduction. In pooled trials it affected 3.3% of people on 2.4 mg (4% of women and 0.9% of men) versus 1% on placebo, and 5.8% on 7.2 mg. Rapid weight loss of any kind can trigger temporary shedding. Eating enough protein helps your body during weight loss; see how much protein you need on a GLP-1.
• Dizziness, low blood pressure and fainting. Low blood pressure was reported in 1.3% of people on semaglutide versus 0.4% on placebo, and fainting in 0.8% versus 0.2%. Some cases were linked to vomiting, diarrhea and fluid loss, and they were more common in people taking blood pressure medicines.
• A faster heart rate. On average, resting heart rate rose by 1 to 4 beats per minute compared with placebo.
• Changes in taste. Altered taste was reported by 1.7% of people versus 0.5% on placebo.
• Injection site reactions. Redness, itching or irritation at the injection site affected 1.4% versus 1% on placebo, so they were uncommon.
• Appendicitis. It occurred in 0.5% of people on semaglutide versus 0.2% on placebo in the weight-loss trials.
• Kidney stones and fractures. In the large heart outcomes trial (SELECT), kidney stones were reported in 1.2% versus 0.8%. Hip and pelvis fractures were more frequent on semaglutide in women (1% versus 0.2%) and in people aged 75 or older (2.4% versus 0.6%).

The serious risks on the FDA label

These side effects are uncommon, but they are the reason the label has a warnings section. Knowing them helps you act quickly if something feels wrong.

Risk	What the label says	Warning signs to watch for
Thyroid C-cell tumors (boxed warning)	Seen in rodents; unknown whether this happens in humans. Not for people with a personal or family history of medullary thyroid cancer or MEN 2.	A lump or swelling in the neck, trouble swallowing, shortness of breath, persistent hoarseness
Acute pancreatitis	Confirmed in 4 people on Wegovy (0.2 cases per 100 patient-years) versus 1 on placebo in weight-loss trials; fatal cases reported after approval.	Severe stomach pain that will not go away, sometimes spreading to the back, with or without vomiting
Gallbladder disease	Gallstones in 1.6% versus 0.7% (injection) and 2.5% versus 1% (tablet); gallbladder inflammation in 0.6% versus 0.2%.	Pain in the upper right belly, fever, yellowing of skin or eyes, clay-colored stools
Acute kidney injury	0.4 versus 0.2 cases per 100 patient-years; often linked to dehydration from vomiting or diarrhea.	Much less urine than usual, swelling, confusion, severe or ongoing vomiting or diarrhea
Low blood sugar	Higher risk with insulin or sulfonylureas.	Shakiness, sweating, confusion, fast heartbeat, dizziness
Severe digestive reactions	Severe events in 4.1% versus 0.9%. Not recommended in severe gastroparesis.	Vomiting you cannot control, being unable to keep fluids down
Serious allergic reactions	Anaphylaxis and angioedema reported.	Swelling of the face, lips, tongue or throat, trouble breathing, severe rash
Diabetic eye disease	In type 2 diabetes, rapid blood sugar improvement can temporarily worsen retinopathy.	Changes in vision
Aspiration during anesthesia	Rare reports of stomach contents being inhaled during sedation.	Tell every surgeon and anesthesiologist you take semaglutide

Source: Wegovy prescribing information, Boxed Warning, sections 5 and 6, and Medication Guide.

After approval, the label also lists reports of bowel blockage (ileus and intestinal obstruction) and severe constipation, including impacted stool. Because reports like these are voluntary, their true frequency is not known. We cover the biggest of these risks in depth in our guides to GLP-1s and pancreatitis and GLP-1s and gallbladder problems.

The eye condition NAION

In June 2025, the European Medicines Agency’s safety committee concluded that NAION (non-arteritic anterior ischemic optic neuropathy), an eye condition that can cause loss of vision, is a very rare side effect of semaglutide medicines, meaning it may affect up to 1 in 10,000 people. It advised that semaglutide be stopped if NAION is confirmed. The US Wegovy label we reviewed does not list NAION, but the practical advice is the same anywhere: if you notice sudden vision loss or rapidly worsening eyesight, contact a doctor without delay.

What about mood and suicidal thoughts?

This was a worry for several years, and the Wegovy label once carried a warning about it. In January 2026, FDA said a comprehensive review found no increased risk of suicidal ideation or behavior with GLP-1 medicines and asked for that warning to be removed from the Wegovy, Zepbound and Saxenda labels. Anyone who notices new or worsening low mood, or thoughts of self-harm, should still reach out to a healthcare professional, whatever the cause.

Everyday ways people ease the common side effects

A 2023 expert consensus from a multidisciplinary panel of endocrinologists, primary care physicians, cardiologists, nephrologists, internists and diabetes nurse educators lists simple habits that may reduce digestive side effects on GLP-1 medicines. These are general habits, not medical instructions, and your prescriber may suggest others.

At meals

• Eat slowly, without distractions, and stop when you feel full.
• Choose smaller portions and, if needed, eat more often.
• Favor easy-to-digest, lower-fat foods, and cook by baking, grilling or boiling rather than frying.
• Avoid lying down right after a meal and avoid eating close to bedtime.

For nausea

• Foods such as crackers, apples, mint and ginger may help.
• Avoid strong smells.

For vomiting or diarrhea

• Pay close attention to fluids; sip small amounts often. Dehydration is the main link between digestive side effects and kidney problems.
• The panel suggests avoiding coffee, alcohol, dairy and fizzy drinks while diarrhea lasts.

For constipation

• Make sure you get enough fiber, drink plenty of water and stay physically active. Our guide to fiber and hydration on GLP-1s has the details.

Keeping a simple food diary can help you spot meals that make symptoms worse. For deeper dives, see our guides to managing GLP-1 nausea, constipation and diarrhea, what to eat on GLP-1s and alcohol and GLP-1s.

Do not start anti-nausea medicine, laxatives or supplements without checking with your prescriber or pharmacist first, especially if you take other prescription medicines. Semaglutide slows stomach emptying and can change how some oral medicines are absorbed. The label notes, for example, that the semaglutide tablet raised levothyroxine (thyroid hormone) levels by about a third in a drug interaction study.

When to call your prescriber, and when to get urgent care

Contact your prescriber soon if you have:

• Nausea, vomiting or diarrhea that does not settle, or that stops you from eating normally.
• Constipation that lasts several days despite fluids and fiber.
• Dizziness or lightheadedness, especially if you take blood pressure medicine.
• Noticeable hair shedding, tingling or burning skin, or a racing heartbeat.
• Low blood sugar symptoms if you also take diabetes medicines.
• Any planned surgery or procedure with sedation.

Get urgent medical care if you have:

• Severe stomach pain that will not go away, with or without vomiting, sometimes spreading to your back.
• Signs of a serious allergic reaction, such as swelling of the face, lips or throat, or trouble breathing.
• Vomiting so severe you cannot keep fluids down, or signs of dehydration such as very little urine.
• Pain in the upper right belly with fever or yellowing of the skin or eyes.
• Sudden loss of vision.
• A severely swollen, painful belly with no bowel movements or gas, which can signal a blockage.

The Medication Guide also says that taking too much semaglutide can cause severe nausea, severe vomiting and severe low blood sugar. In the US, the Poison Help line is 1-800-222-1222.

Who is more likely to have problems

Some groups need extra care, according to the label:

• People with kidney problems had more kidney-related side effects, which occurred more often during dose increases.
• People who take insulin or a sulfonylurea have a higher risk of low blood sugar.
• People who have had bariatric surgery had more episodes of serious low blood sugar in the heart outcomes trial (2.3% versus 0%), though the numbers were small.
• People with type 2 diabetes and existing diabetic retinopathy should be monitored for eye changes.
• People taking blood pressure medicines had more low blood pressure.
• Older adults and women had more hip and pelvis fractures in the heart outcomes trial.
• People who are pregnant or planning pregnancy should not use Wegovy; the Medication Guide says to stop at least 2 months before a planned pregnancy.

For the full list of people who should avoid or use these medicines with caution, see who should not take a GLP-1.

Where your medicine comes from also matters. Side effect data in this article come from trials of the approved products. Unapproved or poorly made semaglutide can carry extra risks, including dosing errors. Our guide to spotting unsafe online GLP-1 sellers explains what to look for.

What people are saying online

On X, semaglutide side effect threads tend to fall into two camps. Some posts simply list nausea, vomiting, diarrhea, stomach pain and constipation, which matches the label. Others swing toward alarm, with screenshots and anecdotes presented as if they were typical. Physicians and science communicators posting about the topic often stress that the common effects tend to ease over time, while serious risks such as pancreatitis and gallbladder problems are uncommon but worth recognizing.

On YouTube, obesity medicine doctors sharing practical tips repeat the same themes as the expert consensus: go slowly with dose increases under your prescriber’s guidance, eat smaller meals, stop at fullness, cut back on greasy food and stay hydrated. That overlap between clinicians’ advice and the published guidance is reassuring.

The balanced view sits between the extremes. Side effects are common, usually manageable and usually temporary, and a small minority of people have serious problems that need prompt care.

Questions to ask your prescriber

1. Which side effects should I expect in the first weeks, and which ones should make me call you?
2. If I have a hard time with side effects, what are my options?
3. Do any of my current medicines, such as diabetes, blood pressure or thyroid medicines, need monitoring or adjusting?
4. Does anything in my history, such as gallstones, pancreatitis, kidney disease or diabetic eye disease, raise my risk?
5. Who do I contact if I have severe symptoms at night or on a weekend?
6. How should I plan around surgery or procedures that need sedation?

Our first 30 days guide can help you prepare for that conversation.

The bottom line

Semaglutide side effects are mostly digestive and mostly temporary. Nausea, diarrhea, vomiting and constipation affect a large share of people, especially around dose increases, but in the trials they were usually mild to moderate and only about 4% of people stopped treatment because of them. Hair loss, dizziness and altered skin sensations are less common and more frequent at the 7.2 mg dose.

Serious problems, including pancreatitis, gallbladder disease, kidney injury from dehydration and serious allergic reactions, are uncommon. Learn their warning signs, keep your prescriber informed and never hesitate to get help for severe or unusual symptoms.

Explore more in our Semaglutide hub, see how the drug performed in semaglutide clinical trial results, or browse every side effect guide in our Side Effects hub.