The most common side effects of GLP-1 medicines such as Wegovy (semaglutide) and Zepbound (tirzepatide) are stomach and gut symptoms: nausea, diarrhea, constipation and vomiting. In the trials behind the labels, 73% of people on Wegovy 2.4 mg and 56% of people on Zepbound reported a gut side effect, compared with 47% and 30% on placebo. Both labels say these effects happen most often while the dose is being stepped up and ease over time, and most were mild to moderate. A small number of people get serious problems, such as pancreatitis or gallbladder disease, so it helps to know the warning signs.
Key takeaways
- Nausea is the most common side effect: 44% on Wegovy 2.4 mg vs 16% on placebo, and 25% to 29% on Zepbound vs 8% on placebo, according to the US labels.
- Gut symptoms are most common during the dose step-ups. Wegovy steps up every 4 weeks until week 17; Zepbound starts at 2.5 mg for 4 weeks and rises in 2.5 mg steps.
- 4.3% of people on Wegovy 2.4 mg (vs 0.7% on placebo) and 1.9% to 4.3% on Zepbound (vs 0.5%) stopped treatment because of gut side effects.
- Hair shedding was reported in 3% on Wegovy and 4% to 5% on Zepbound (vs 1% on placebo). Both labels link it to weight loss, and it was more common in women.
- Severe stomach pain that will not go away, especially if it spreads to your back, can be a sign of pancreatitis. Get medical care right away; the labels say the medicine should be stopped if pancreatitis is suspected.
- Both medicines carry a boxed warning about thyroid C-cell tumors seen in rats. A lump in your neck, trouble swallowing or ongoing hoarseness should be checked by your clinician.
What are the most common GLP-1 side effects?
The most common side effects are nausea, diarrhea, vomiting and constipation, followed by belly pain, indigestion, burping, reflux, tiredness and headache. The table shows how often each one was reported in the placebo-controlled weight-loss trials listed in each US prescribing label.
| Side effect | Wegovy 2.4 mg | Placebo (Wegovy trials) | Zepbound 5 to 15 mg | Placebo (Zepbound trials) |
|---|---|---|---|---|
| Nausea | 44% | 16% | 25% to 29% | 8% |
| Diarrhea | 30% | 16% | 19% to 23% | 8% |
| Vomiting | 24% | 6% | 8% to 13% | 2% |
| Constipation | 24% | 11% | 11% to 17% | 5% |
| Belly pain | 20% | 10% | 9% to 10% | 5% |
| Indigestion (dyspepsia) | 9% | 3% | 9% to 10% | 4% |
| Headache | 14% | 10% | not listed | not listed |
| Tiredness (fatigue) | 11% | 5% | 5% to 7% | 3% |
| Dizziness | 8% | 4% | 4% to 5% | 2% |
| Burping (eructation) | 7% | under 1% | 4% to 5% | 1% |
| Reflux (GERD) | 5% | 3% | 4% to 5% | 2% |
| Hair loss | 3% | 1% | 4% to 5% | 1% |
| Injection-site reactions | 1.4% | 1% | 6% to 8% | 2% |
Wegovy figures come from three trials with 2,116 adults on 2.4 mg for up to 68 weeks. Zepbound figures come from two trials (SURMOUNT-1 and SURMOUNT-2) with 2,519 adults treated for up to 72 weeks; the range covers the 5, 10 and 15 mg doses. "Not listed" means the effect was not in that label's table of reactions more common than placebo. The labels warn that rates from different trials cannot be compared directly, so this table shows what to expect, not which drug is gentler.
The daily Wegovy pill (25 mg) had side effects similar in type and frequency to the injection, according to its label. At the higher 7.2 mg Wegovy injection dose, the label reports more nausea (39%) and vomiting (22%), and changes in skin feeling, such as tingling or burning, in 22% of people.
When do side effects start and how long do they last?
Side effects usually start in the first weeks and come back, often milder, after each dose increase. Both labels say most nausea, vomiting and diarrhea happened during dose escalation and decreased over time. The STEP 1 trial of semaglutide described nausea and diarrhea as "typically transient and mild-to-moderate". The SURMOUNT-1 trial of tirzepatide reported that gut events occurred mostly during dose escalation.
| Phase | Wegovy (label schedule) | Zepbound (label schedule) | What many people notice |
|---|---|---|---|
| Weeks 1 to 4 | 0.25 mg starting dose | 2.5 mg starting dose | Less hunger, early fullness, some nausea |
| Weeks 5 to 16 | Steps up every 4 weeks: 0.5, 1, 1.7 mg | 5 mg from week 5, then possible 2.5 mg steps after at least 4 weeks on each dose | Nausea or bowel changes often come back for a while after a step-up |
| Week 17 onward | Maintenance dose (1.7 or 2.4 mg) | Maintenance dose (5, 10 or 15 mg); 15 mg is reached at week 21 at the earliest | Gut symptoms usually settle |
This is what the labels describe, not a plan for you. Your prescriber sets your doses and may hold a step longer if side effects are hard. The titration schedules tool lays out each label schedule side by side.
Many people find symptoms are strongest in the days right after their shot. Keeping a simple note of how you feel each day shows you your own pattern, which is more useful than any average.
What helps with nausea, constipation and diarrhea?
Eating less at a time and stopping as soon as you feel full helps most people. These medicines slow how fast your stomach empties, so a meal that used to feel normal can now sit heavy. Some simple habits:
- Smaller meals, eaten slowly. Stop at the first sign of fullness, even if food is left on the plate.
- Protein first. Start meals with protein, such as eggs, yogurt, fish, chicken, tofu or beans, so the most important food gets eaten before you fill up.
- Go easy on greasy, fried and very rich food. These sit longest in the stomach and are common nausea triggers.
- Sip fluids through the day. Water, broth and drinks with electrolytes help, especially if you have diarrhea or vomiting. The water calculator gives you a daily target.
- Add fiber gradually. Fruit, vegetables, oats and beans help with constipation, but adding a lot at once can cause gas and bloating. Raise it slowly and drink more as you do.
- Do not lie down right after eating. This can help with reflux and burping.
If constipation lasts more than a few days or diarrhea will not stop, talk to your clinician or pharmacist before trying a new remedy.
Why do GLP-1s cause tiredness, headache and hair shedding?
Tiredness, headache and hair shedding are usually linked to eating much less and losing weight quickly. Tiredness was reported in 11% on Wegovy and 5% to 7% on Zepbound. Headache was reported in 14% on Wegovy vs 10% on placebo. Low food intake, too little fluid and poor sleep can all add to both.
Both labels say hair loss was associated with weight loss. On Wegovy 2.4 mg it was reported in 4% of women and 0.9% of men; on Zepbound in 7.1% of women and 0.5% of men. In the Zepbound trials, no one stopped treatment because of it. Enough protein and steady eating help, and shedding linked to fast weight loss often settles with time.
What happens at the injection site?
Mild redness, itching, bruising or pain where you inject is the most common skin reaction. It was reported in 6% to 8% of people on Zepbound and 1.4% on Wegovy. Rotating sites, such as belly, thigh and upper arm, helps the skin recover. A rash that spreads, hives, or swelling of your face, lips or throat is different: that can be an allergic reaction.
Which GLP-1 side effects are serious?
Serious side effects are uncommon, but both labels list warning signs that need prompt care. Gut side effects were severe in 4.1% on Wegovy and 1.7% to 3.1% on Zepbound.
Get medical care right away if you have severe stomach pain that will not go away (with or without vomiting), signs of an allergic reaction such as swelling of the face, lips, tongue or throat, trouble breathing or a fast heartbeat, or signs of dehydration such as very little urine, dizziness or confusion.
- Pancreatitis. Severe, ongoing belly pain, sometimes spreading to the back, is the key sign. The labels say to stop the medicine if pancreatitis is suspected. Seek care right away.
- Gallbladder problems. Gallstones were reported in 1.6% on Wegovy (vs 0.7% on placebo) and 1.1% on Zepbound (vs 1%). Pain in the upper right belly, fever, yellow skin or eyes, or clay-colored stools need a call to your clinician.
- Kidney injury from dehydration. Repeated vomiting or diarrhea can dry you out and strain your kidneys. If you cannot keep fluids down, contact your clinician.
- Low blood sugar with diabetes medicines. If you have type 2 diabetes, low blood sugar was more common on Wegovy (6.2% vs 2.5%) and Zepbound (4.2% vs 1.3%), and more likely with insulin or a sulfonylurea. Shakiness, sweating, confusion or a racing heart are the signs. Your prescriber may adjust your other medicines.
- Thyroid C-cell tumors (boxed warning). These tumors were seen in rats; it is not known if this happens in people. Do not use these medicines if you or a family member has had medullary thyroid cancer or MEN 2. Tell your clinician about a neck lump, trouble swallowing, shortness of breath or hoarseness that does not go away.
- Allergic reactions. Serious reactions, including anaphylaxis and swelling (angioedema), have been reported. Get emergency help.
- Surgery or sedation. These medicines slow stomach emptying. Tell your care team you take one before any procedure that needs anesthesia or deep sedation.
How Morning helps
Morning keeps a shot log with the dose plan you and your clinician set, and its side-effect check-ins show whether your nausea or tiredness clusters around shot day. The food photo scan counts protein, fiber and water toward your daily targets, which covers most of the habits above. Ask Sunny, your chat coach, can talk through food and side-effect questions any time, though never dose advice, and the doctor report gathers your notes to bring to appointments.
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Questions
How long do GLP-1 side effects last?
For most people, gut side effects are worst in the first weeks and after each dose increase, then ease. Both the Wegovy and Zepbound labels say most nausea, vomiting and diarrhea happened during dose escalation and decreased over time.
Are side effects worse on semaglutide or tirzepatide?
The labels list similar side effects for both, and they warn that rates from different trials cannot be compared directly. Your own experience depends on your dose, how fast it rises and how you eat, so track your pattern and share it with your prescriber.
Do side effects mean the medicine is working?
Not necessarily. Many people lose weight with few or no side effects. Side effects reflect how your gut reacts to the medicine, not how much weight you will lose.
What should I do if I cannot keep fluids down?
Contact your clinician the same day. Repeated vomiting or diarrhea can lead to dehydration and, in some cases, kidney injury, which both labels warn about.
Should I skip or lower a dose if I feel sick?
That is a decision for your prescriber. Follow your prescriber and the label; the labels allow a prescriber to delay a step-up or choose a lower maintenance dose when side effects are hard.
Is hair loss on a GLP-1 permanent?
Both labels link hair loss to weight loss rather than to the medicine directly, and in the Zepbound trials no one stopped treatment because of it. Shedding linked to fast weight loss often settles over time; if it worries you, ask your clinician.
Sources
- Wegovy (semaglutide) US prescribing information, Novo Nordisk
- Zepbound (tirzepatide) US prescribing information, Eli Lilly
- DailyMed: Wegovy label
- DailyMed: Zepbound label
- Wilding JPH et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med 2021;384:989-1002
- Jastreboff AM et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med 2022;387:205-216
Keep reading
Educational information, not medical advice. Talk to your clinician about your treatment.