Weight Loss · Reference
Semaglutide Side Effects: Common, Serious, and What to Report
This page is a practical reference: what to expect, when, what helps, and what to report. The broader question of overall safety, including the long-term trials and what the FDA has said about compounded semaglutide, is covered in is semaglutide safe and is compounded semaglutide safe.
Medically reviewed by Dr. Gene, MD · November 4, 2026
Treatments mentioned
The most common semaglutide side effects are nausea, diarrhea, vomiting, constipation and abdominal pain, and they are worst in the days after starting and after each dose increase. On the approved weight-management label, nausea was reported by 44% of adults on the top dose against 16% on placebo, and most gastrointestinal effects were mild to moderate and transient. The serious side effects are uncommon: pancreatitis, gallbladder disease, dehydration that can injure the kidneys, and allergic reactions. A personal or family history of medullary thyroid carcinoma or MEN 2, pregnancy and breastfeeding rule semaglutide out.
This page is a practical reference: what to expect, when, what helps, and what to report. The broader question of overall safety, including the long-term trials and what the FDA has said about compounded semaglutide, is covered in is semaglutide safe and is compounded semaglutide safe.
Semaglutide Side Effects
The short answer
| Side effect | Semaglutide on the approved label | Placebo | What to do |
|---|---|---|---|
| Nausea | 44% | 16% | Smaller meals, eat slowly, report it |
| Diarrhea | 30% | 16% | Fluids; report if it persists |
| Vomiting | 24% | 6% | Report it; not keeping fluids down is a same-day call |
| Constipation | 24% | 11% | Fluid, fiber, movement; report it by name |
| Abdominal pain | 20% | 10% | Report it; severe pain into the back is a same-day call |
| Headache | 14% | 10% | Often linked to eating and drinking less early on |
| Fatigue | 11% | 5% | Same; report if it persists |
These rates come from three placebo-controlled trials in 2,116 adults treated at 2.4 mg weekly for up to 68 weeks. The medication this page covers:
| Product | What is in it | Price |
|---|---|---|
| Semaglutide | Dose-specific vials at six strengths, starting with 1 mg per 1 mL at the 0.25 mg starting dose | From $99/mo, priced by dose |
The price is all-in: medication, physician review, refill management and shipping, with no membership fee. Pepti's semaglutide is compounded by a PCAB-accredited, FDA-registered US 503A pharmacy and contains no B12. Compounded medications are not FDA approved. The rates on this page come from trials of the approved manufactured product, which contains the same molecule, so the same side effects apply.
Semaglutide Side Effects
Common semaglutide side effects
Semaglutide is a GLP-1 receptor agonist, a modified copy of a hormone the gut releases after eating. It slows the rate at which the stomach empties and acts on appetite centers in the brain. Nearly every common side effect is that mechanism working: a slower stomach produces early fullness, nausea, reflux and constipation, and reduced appetite can tip into eating and drinking too little.
The full list from the approved label
Side effect Semaglutide 2.4 mg Placebo Nausea 44% 16% Diarrhea 30% 16% Vomiting 24% 6% Constipation 24% 11% Abdominal pain 20% 10% Headache 14% 10% Fatigue 11% 5% Dyspepsia (indigestion) 9% 3% Dizziness 8% 4% Abdominal distension (bloating) 7% 5% Belching 7% under 1% Flatulence 6% 4% Reflux 5% 3% Hair loss 3.3% 1% Altered taste 1.7% 0.5% Injection-site reactions 1.4% 1.0% Low blood pressure 1.3% 0.4% Fainting 0.8% 0.2% Overall, 73% of adults on semaglutide and 47% on placebo reported some gastrointestinal side effect. Read the placebo column first: 16% of people on a dummy injection reported nausea and 5% reported fatigue. Not everything you feel on semaglutide is the drug. Low blood pressure and fainting were more frequent in people already taking blood-pressure medication.
Heart rate
Resting heart rate rose by an average of 1 to 4 beats per minute against placebo, and more people on semaglutide had an increase of 20 beats per minute or more at some visit (26% against 16%). The label asks for heart rate to be checked at routine intervals. Palpitations or a racing heart at rest are worth reporting.
How many people stop
In the pooled trials, 6.8% of adults on semaglutide and 3.2% on placebo stopped permanently because of a side effect. Stopping for a gastrointestinal reason was 4.3% against 0.7%. In SELECT, a much longer trial in older adults with heart disease, 16.6% stopped for an adverse event against 8.2% on placebo. So most people continue, and the share who stop rises with age and length of treatment.
Semaglutide Side Effects
When side effects show up in the dose ladder
The approved label states that gastrointestinal reactions increased during dose escalation, and it instructs prescribers to follow the escalation schedule to minimize them. The approved adult schedule is four weeks each at 0.25 mg, 0.5 mg, 1 mg and 1.7 mg once weekly before a maintenance dose.
| Pepti strength | Vial | Draw |
|---|---|---|
| 0.25 mg weekly, the starting dose | 1 mg per 1 mL (1 mg/mL) | 0.25 mL (25 units) |
| 0.5 mg weekly | 2 mg per 2 mL (1 mg/mL) | Printed on the vial |
| 1 mg weekly | 4 mg per 2 mL (2 mg/mL) | Printed on the vial |
| 1.7 mg weekly | 7.5 mg per 3 mL (2.5 mg/mL) | 0.68 mL (68 units) |
| 2 mg weekly | 10 mg per 2 mL (5 mg/mL) | Printed on the vial |
| 2.5 mg weekly | 10 mg per 2 mL (5 mg/mL) | Printed on the vial |
Because each strength is a separate vial at its own concentration, the number of units you draw can change when the strength changes. Never carry a number over from a previous vial; read the new label. The arithmetic is in how long does a peptide vial last.
What patients commonly describe
Point in treatment What is typical First days at the starting dose Early fullness, some queasiness, appetite change First days after each step up The peak of it: nausea, fullness, sometimes reflux Weeks at the same strength Usually easing After two or more missed doses Tolerance fades, so restarting can feel like the beginning again These are patterns, not promises. Some people barely notice the steps, some feel every one, and some cannot tolerate semaglutide at all.
Holding and stepping back are built into the rules
The approved label says that if a dose is not tolerated during escalation, the next increase can be delayed for four weeks, and that an untolerated top maintenance dose can be reduced to 1.7 mg. If side effects have not settled, tell your care team before the next step. Your physician sets your directions after reviewing how you are doing, and they are printed on the vial. Never change your own dose.
Why missed doses matter
The approved label states that if two or more consecutive doses are missed, escalation restarts at a lower dose to reduce gastrointestinal side effects. Stopping for a few weeks and restarting at the old strength is the reliable way to relive the first week. Message your care team before restarting after a gap.
Why side effects fade slowly after stopping
Semaglutide has an elimination half-life of about a week, and the label notes it stays in circulation for roughly five to seven weeks after the last dose. A side effect tapers over weeks rather than hours.
Semaglutide Side Effects
Semaglutide GI side effects and what helps
These measures are grounded in how the drug works and in clinical experience, not in trials that randomized people to eating advice. They are low-risk and sensible.
| Symptom | What usually helps | When to tell your care team |
|---|---|---|
| Nausea | Smaller portions, stop at the first fullness, eat slowly, protein first, avoid fried and very fatty food | If you are not eating properly, or it is not easing at the same strength |
| Constipation | Fluid, fiber, regular movement | If it persists; name it specifically, because the answer differs from nausea |
| Diarrhea | Fluids, plain meals | If it lasts more than a day or two, or you feel dizzy |
| Reflux, belching, bloating | An earlier last meal, staying upright after eating, less alcohol | If it wakes you or is not responding |
| Vomiting | Small sips of fluid | Same day if you cannot keep fluids down |
| Headache, fatigue, dizziness | Regular meals with enough protein and fluid | If they persist |
Pepti physicians can prescribe ondansetron for nausea where they judge it appropriate. It treats the symptom; if the dose has climbed faster than your stomach can adapt, slowing the schedule is still the main answer. The longer guide is GLP-1 nausea: how to manage it, and alcohol is covered in can you drink alcohol on semaglutide.
The dehydration and kidney link
Acute kidney injury occurred in 0.4 per 100 patient-years on semaglutide in the pooled trials, and post-marketing reports, some needing dialysis, were mostly in people whose nausea, vomiting or diarrhea led to dehydration. The label now names the section after that mechanism: kidney injury due to volume depletion. Drink, and report vomiting that lasts more than a day.
Semaglutide Side Effects
Serious side effects of semaglutide: what to report urgently
| Symptom | What it may be | What to do |
|---|---|---|
| Severe, persistent abdominal pain, sometimes into the back, with or without vomiting | Acute pancreatitis | Seek medical care the same day; stop the medication if pancreatitis is suspected |
| Pain under the right ribs, fever, yellowing skin or eyes | Gallstones or gallbladder inflammation | Seek care the same day |
| Not keeping fluids down, dark urine, not passing urine | Dehydration, with a risk to the kidneys | Contact your care team the same day |
| Swollen, painful abdomen, vomiting that will not stop, no gas or stool | Bowel obstruction or ileus | Emergency care |
| Swelling of the face, lips or throat, widespread rash, trouble breathing | Serious allergic reaction | Emergency care first |
| A lump in the neck, persistent hoarseness, trouble swallowing | The thyroid symptoms the label asks people to watch for | Contact your physician promptly |
| Shakiness, sweating, confusion, if you take insulin or a sulfonylurea | Low blood sugar | Treat it, then report it |
| Sudden vision loss, or worsening vision with diabetic retinopathy | Needs urgent assessment | Urgent eye care and a message to your care team |
| A racing heart at rest | Heart rate increase | Report it |
How often the serious ones happened
Confirmed acute pancreatitis occurred in 4 adults on semaglutide in the pooled trials, about 0.2 cases per 100 patient-years, against 1 on placebo. Gallstones were reported by 1.6% against 0.7%, and gallbladder inflammation by 0.6% against 0.2%; the label notes the excess persisted after accounting for the amount of weight lost. Severe gastrointestinal reactions were 4.1% against 0.9%. Ileus, intestinal obstruction and severe constipation including fecal impaction have been reported after approval, where frequency cannot be estimated.
Low blood sugar
On its own, semaglutide lowers glucose only when it is high and rarely causes low blood sugar. With insulin or a sulfonylurea the risk rises; in the trial of adults with type 2 diabetes, clinically significant low blood sugar was 6.2% against 2.5%. The label also singles out a history of bariatric surgery as a risk factor in people without diabetes.
Eyes
In people with type 2 diabetes and existing retinopathy, rapid improvement in glucose has been linked with temporary worsening: in SUSTAIN-6, retinopathy complications were 3.0% against 1.8%. Separately, a 2024 observational study in JAMA Ophthalmology reported an association with NAION, a rare cause of sudden painless vision loss in one eye; it cannot establish cause, and the US label carries no NAION warning as of its June 2026 revision. Sudden vision loss is urgent either way.
The thyroid warning
The approved label carries a boxed warning because semaglutide caused thyroid C-cell tumors in rodents. Whether it does in people is unknown. That is why a personal or family history of medullary thyroid carcinoma or MEN 2 rules it out. The detail is in is semaglutide safe.
Before surgery, sedation or a colonoscopy
Because the stomach empties slowly, there are rare reports of food still in the stomach and aspiration under general anesthesia or deep sedation despite normal fasting. Tell the team before any planned procedure and let them plan with your prescriber.
Semaglutide Side Effects
Semaglutide side effects in women
| Topic | What the sources say | What it means in practice |
|---|---|---|
| Hair loss | 3.3% against 1% on placebo, almost entirely in women; the label attributes it to weight reduction | Report it; protein intake and the pace of change matter |
| Bone fractures | In SELECT, hip and pelvis fractures were more frequent on semaglutide in women (1.0% against 0.2%) | Bone health and frailty get a closer look, especially over 75 |
| Fertility | Weight loss can bring back ovulation in people who had stopped ovulating | Pregnancy is possible even if it was not before; plan contraception |
| Pregnancy | Stop when pregnancy is recognized, and at least two months before a planned pregnancy because of the long half-life | Tell your care team early if you are planning a pregnancy |
| Breastfeeding | No human data | Not prescribed while breastfeeding |
More on this is in do peptides affect fertility and peptides for women.
Semaglutide Side Effects
Who should not take semaglutide
| Situation | Status |
|---|---|
| Personal or family history of medullary thyroid carcinoma | Rules it out |
| Multiple endocrine neoplasia type 2 (MEN 2) | Rules it out |
| Previous serious allergic reaction to semaglutide or an ingredient of the vial | Rules it out |
| Pregnancy, or planning pregnancy within two months | Not used |
| Breastfeeding | Not used |
| Severe gastroparesis | Not recommended |
| Previous pancreatitis | Not automatic, but needs careful discussion |
| Active gallbladder disease | Needs discussion |
| Diabetic retinopathy | Needs monitoring |
| Taking another GLP-1 medication, including tirzepatide | Not combined |
| Under 18 | Pepti prescribes to adults only |
Bloodwork is not required for any Pepti treatment. If your physician wants labs for your care, they'll ask through your account.
Semaglutide Side Effects
Semaglutide vs tirzepatide side effects
They share the same side-effect categories, serious risks and contraindications. Their label percentages come from different trials in different populations and cannot be compared directly. The comparison is in semaglutide vs tirzepatide; the tirzepatide version of this page is tirzepatide side effects, and the class overview is GLP-1 side effects.
Semaglutide Side Effects
What the evidence shows, honestly
Semaglutide's side-effect profile comes from large randomized trials, outcome trials running several years, and years of reports after approval. Its common effects, serious risks and contraindications are documented rather than inferred.
The limits: the trial rates belong to the approved manufactured product, not to any compounded preparation, though the molecule and therefore the side effects are the same. The eating advice is sensible but untested in trials. Post-marketing events have no reliable frequency. And claims that a compounded version, or a vitamin added to the vial, reduces nausea have no trial behind them.
One risk specific to compounded vials is dosing error. The FDA has received reports of people drawing the wrong amount from multi-dose vials, which is why Pepti prints the dose in both millilitres and syringe units for the exact vial you receive. If the label does not match what you expected, do not inject; message your care team.
Semaglutide Side Effects
Where to get semaglutide prescribed
Semaglutide cannot be bought legitimately without a prescription. Products sold "for research use only" have no accountable pharmacy behind their identity, purity, sterility or concentration. The prescription route:
- Complete a free online intake covering your history, medications and what you want help with.
- A physician licensed in your state reviews it, usually within 24 hours.
- If it is appropriate, a state-licensed, FDA-registered US pharmacy compounds it to that prescription. Lot test results are published at /quality/lab-results.
- It ships refrigerated with ice packs, with sterile syringes and alcohol prep pads, and your directions printed on the vial.
- Your care team stays reachable for side effects and dose questions. Refills run every 28 days, one vial per fill.
Pepti is cash-pay and does not bill insurance. The step-by-step page is how to get semaglutide prescribed online.
References
What this is based on.
References
- Wilding JPH, Batterham RL, Calanna S, et al.. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1) · New England Journal of Medicine (2021) · PMID 33567185
- Lincoff AM, Brown-Frandsen K, Colhoun HM, et al.. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT) · New England Journal of Medicine (2023) · PMID 37952131
- Wadden TA, Bailey TS, Billings LK, et al.. Effect of subcutaneous semaglutide vs placebo as an adjunct to intensive behavioral therapy on body weight in adults with overweight or obesity (STEP 3) · JAMA (2021) · PMID 33625476
- Rubino D, Abrahamsson N, Davies M, et al.. Effect of Continued Weekly Subcutaneous Semaglutide vs Placebo on Weight Loss Maintenance in Adults With Overweight or Obesity: The STEP 4 Randomized Clinical Trial · JAMA (2021) · PMID 33755728
- Marso SP, Bain SC, Consoli A, et al.. Semaglutide and Cardiovascular Outcomes in Patients with Type 2 Diabetes (SUSTAIN-6) · New England Journal of Medicine (2016) · PMID 27633186
- Davies M, Færch L, Jeppesen OK, et al.. Semaglutide 2.4 mg once a week in adults with overweight or obesity, and type 2 diabetes (STEP 2): a randomised, double-blind, double-dummy, placebo-controlled, phase 3 trial · The Lancet (2021) · PMID 33667417
- Garvey WT, Batterham RL, Bhatta M, et al.. Two-year effects of semaglutide in adults with overweight or obesity: the STEP 5 trial · Nature Medicine (2022) · PMID 36216945
- Rubino DM, Greenway FL, Khalid U, et al.. Effect of Weekly Subcutaneous Semaglutide vs Daily Liraglutide on Body Weight in Adults With Overweight or Obesity Without Diabetes: The STEP 8 Randomized Clinical Trial · JAMA (2022) · PMID 35015037
- Aronne LJ, Horn DB, le Roux CW, et al.. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5) · New England Journal of Medicine (2025) · PMID 40353578
- Sanyal AJ, Newsome PN, Kliers I, et al.. Phase 3 Trial of Semaglutide in Metabolic Dysfunction-Associated Steatohepatitis (ESSENCE) · New England Journal of Medicine (2025) · PMID 40305708
- Wilding JPH, Batterham RL, Davies M, Van Gaal LF, Kandler K et al.. Weight regain and cardiometabolic effects after withdrawal of semaglutide: The STEP 1 trial extension · Diabetes Obes Metab (2022) · PMID 35441470
- Batsis JA, Gavras A, Gross DC, Cheever CR, Da Silva BR et al.. Effect of Incretin-Based and Nonpharmacologic Weight Loss on Body Composition: A Systematic Review · Ann Intern Med (2026) · PMID 41996180
Citations are provided for educational purposes. They do not constitute medical advice. Always discuss any peptide protocol with your prescribing physician.
Common questions
Semaglutide Side Effects, answered.
Nausea (44% against 16% on placebo), diarrhea (30% against 16%), vomiting (24% against 6%), constipation (24% against 11%) and abdominal pain (20% against 10%), on the approved weight-management label at 2.4 mg. Most were mild to moderate and clustered around dose increases.
The approved label states that gastrointestinal reactions increased during dose escalation, and most people describe them easing at a steady strength. There is no fixed timeline. Because semaglutide stays in circulation for five to seven weeks after a last dose, effects also fade slowly after stopping.
Acute pancreatitis, gallbladder disease, kidney injury from dehydration, severe gastrointestinal reactions including bowel obstruction, serious allergic reactions, low blood sugar with insulin or a sulfonylurea, and retinopathy complications in people with diabetes. Each is uncommon, and each has a recognizable warning sign listed above.
Hair loss was reported in 3.3% against 1% on placebo, almost entirely in women, and the label attributes it to weight reduction rather than a direct drug effect. Report it, and keep protein intake up.
Headache was reported in 14% against 10% on placebo, and fatigue in 11% against 5%. Both are often linked to eating and drinking less in the early weeks. Report either if it persists.
Slightly, on average: 1 to 4 beats per minute against placebo. A racing heart at rest should be reported, and the label asks for heart rate to be checked at routine intervals.
Severe abdominal pain that persists or goes through to the back; a swollen, painful abdomen with vomiting and no gas or stool; swelling of the face, lips or throat or trouble breathing; and sudden vision loss. Not keeping fluids down or right-sided upper abdominal pain with fever needs same-day care.
Ask your care team. Pepti physicians can prescribe ondansetron where they judge it appropriate. Slowing the pace of increases is usually the bigger lever.
Yes. It is the same molecule, so the same side effects, serious risks and contraindications apply. Compounded medications are not FDA approved; what differs is the preparation, covered in is compounded semaglutide safe.
Current evidence does not support it. A Nature Medicine cohort of over 240,000 people reported lower rates of suicidal ideation on semaglutide than on other weight-management drugs, and the approved weight-management label's suicidal-behavior warning was removed in February 2026. Any change in mood should still be reported.
Tell the team in advance. The label records rare aspiration under anesthesia or deep sedation because food can remain in the stomach, and says data are insufficient to know whether stopping beforehand helps. The team plans it with your prescriber. The free assessment goes to a physician licensed in your state. A consultation does not guarantee a prescription.
Next step
See what a physician recommends for you.
A licensed physician in your state reviews your intake and decides what is appropriate. A consultation does not guarantee a prescription.