GLP-1 and peptide side effects: when to see a doctor

Which symptoms mean call 911, get care today, or tell your doctor?

Call 911 for signs of a severe allergic reaction, heart attack, stroke, sepsis or very low blood sugar. Get care the same day for severe belly pain, vomiting that won’t stop, or a spreading infection. Tell your doctor about the rest.

We sorted these by what FDA-approved labels and CDC, NIH and FDA pages tell people to do. Where a source gives no timeframe, the level is our call and says so. When in doubt, get checked.

Which GLP-1 side effects are common, and do they go away?

Nausea, diarrhea, vomiting and constipation are the most common, mostly while the dose is being raised, and they usually ease over time. On Wegovy 2.4 mg, 44% of people had nausea, compared with 16% on placebo.

• They’re worst early on. Stomach side effects were most common while the dose was being raised, and on Zepbound most nausea, vomiting and diarrhea eased over time.^7,8
• Higher doses bring more of them. On Wegovy HD, 22% of people vomited, compared with 16% on the 2.4 mg dose, and 22% noticed changed skin sensations, compared with 6%.⁷
• A few people stop. On Wegovy 2.4 mg, 4.3% of people stopped because of stomach side effects, compared with 0.7% on placebo. Hair loss affected 3% of people on Wegovy and 1% on placebo.⁷
• PT-141 follows its own pattern. On Vyleesi, nausea usually starts within an hour of a dose and lasts about 2 hours, and is worst after the first dose. Blood pressure rises after every dose and is usually back to normal within 12 hours.¹⁷

What serious problems do GLP-1 drug labels warn about?

Pancreatitis, gallbladder problems, kidney injury from dehydration, severe allergic reactions, low blood sugar alongside diabetes drugs, and a boxed warning about thyroid tumors seen in rodents.

• Thyroid tumors in rodents. Wegovy, Zepbound and Foundayo carry a boxed warning about thyroid tumors seen in rodents; whether the risk applies to people is unknown. Don’t take them if you or a family member has had medullary thyroid cancer, or if you have MEN 2.^7,8,13
• Pancreatitis, sometimes fatal. Inflammation of the pancreas has been seen with GLP-1 drugs, including deaths. The sign to watch for is severe belly pain that won’t go away, sometimes felt through to the back.⁷
• Dehydration can hurt the kidneys. Acute kidney injury, sometimes bad enough to need dialysis, has been reported, mostly after vomiting or diarrhea caused dehydration. Drink enough fluids.^7,8,13
• Low blood sugar, alongside diabetes drugs. In people with type 2 diabetes on tirzepatide, 10.3% of those also taking a sulfonylurea had blood sugar under 54 mg/dL, compared with 2.1% of those who weren’t.⁸
• Tell your doctor before any procedure. In rare cases, food or liquid got into the lungs of people under anesthesia or deep sedation, even when they had fasted as told.^7,8,13
• Never share a pen, even with a new needle. The labels added this warning in 2026, because a shared pen can spread blood-borne infections.^7,8
• The suicidal-thoughts warning came off. In January 2026, after reviewing 91 trials with 107,910 people, FDA found no increased risk and asked for the warning to be removed from the labels. It still asks people to report new or worse depression.²
• Sudden vision loss, very rarely. Europe’s regulator lists NAION, an eye-nerve stroke, as a very rare side effect of semaglutide, in up to 1 in 10,000 people, and the UK says to go urgently to an eye emergency department if it happens. It isn’t on US labels: FDA listed it as a possible risk under evaluation in its report covering late 2024, and we found no FDA action since.^19,20,43,44

What are the risks of unapproved peptides like BPC-157?

Largely unknown. They have no FDA label, so no tested list of warning signs. FDA found too little human safety data on BPC-157 to judge it, and the warnings for melanotan II and MK-677 come from case reports and a trial stopped early.

• BPC-157 has little human data. FDA’s July 2026 review found five small human studies, none using the under-the-skin, oral or nasal routes people actually use, and three reports to FDA of problems after injections: redness and swelling where it went in, shortness of breath that led to an ER visit, and darkened skin and gums. FDA says it’s unclear whether BPC-157 caused them.¹¹ A separate 2026 review found three human studies with 30 people in all, every one of poor quality.⁴⁵ BPC-157 profile
• A vote isn’t a safety finding. FDA’s outside advisers voted 8–6 in July 2026, ABC News reported, to recommend BPC-157 for pharmacy compounding, against FDA reviewers’ advice. The vote isn’t binding.^46,47
• Melanotan II is on FDA’s risk list. FDA lists it among compounding ingredients that may pose significant safety risks:⁴⁸

• What the case reports describe. One man who injected 6 mg spent 3 days in intensive care with muscle breakdown and kidney injury. A 2017 review counted four melanoma reports in melanotan users but found no proof the drug caused them.^36,41
• MK-677 (ibutamoren): a trial stopped early. A trial in 123 older adults recovering from hip fractures was stopped early over heart failure, and FDA lists it as a significant safety risk. In a year-long trial, it raised blood sugar and HbA1c.^38,40,48
• Others on FDA’s list. CJC-1295: a raised heart rate and a body-wide reaction of the blood vessels. Ipamorelin: serious events including a death when given IV in a study. GHRP-6: possible effects on cortisol and blood sugar. TB-500 and MOTS-c: FDA found no data on people taking them.⁴⁸
• Approved relatives have labels. PT-141 is sold as Vyleesi, melanotan I as Scenesse, and growth hormone and tesamorelin are approved drugs. Their labels list the known risks, from raised blood pressure on Vyleesi to fluid retention and higher blood sugar on growth hormone and tesamorelin.^{14,17,18,39,49}
• When it goes wrong, nobody may know why. Two women were put on breathing tubes after peptide injections at a 2025 anti-aging festival in Las Vegas. Nevada’s pharmacy board couldn’t determine the cause or test the products.⁵⁰
• No established safety profile. A 2026 physician review says unapproved peptides such as BPC-157, TB-500 and melanotan II lack established human safety profiles.⁵¹

Can a contaminated or compounded product make you sick?

Yes. Bacterial toxins in an injection can cause fever, chills and shock within hours, and contaminated injections have caused outbreaks. FDA doesn’t review compounded drugs before they’re sold.

• Bacterial toxins act fast. FDA says too much endotoxin in an injection can cause fever, chills, muscle pain, headache, nausea, vomiting, low blood pressure, shock and death. In CDC-led studies of a contaminated IV drug, reactions came within 3 hours.^22,34,52
• A 2026 example. At least 30 people had fever, chills and shock-like symptoms after IV glutathione compounded from supplement-grade powder. Some were hospitalized.⁵³
• Contaminated injections have caused outbreaks. Contaminated steroid shots from one compounding pharmacy caused 753 fungal infections and 64 deaths in 20 states in 2012. An unapproved “stem cell” product put 12 people in hospital in 2018, and counterfeit Botox harmed 17 people in 9 states in 2024.^54,55,56
• No review before sale. Compounded drugs don’t go through FDA review for safety, effectiveness or quality before they’re sold.⁵⁷ What each kind of vial guarantees

What should you do if you took too much?

Call Poison Help at 1-800-222-1222 right away, even if you feel fine; it’s free and open around the clock. Call 911 if the person has collapsed, has trouble breathing or has severe chest pain.

• Call Poison Help first. 1-800-222-1222 connects you to your local poison center. It’s free and confidential, answered by pharmacists, nurses, doctors and other poison experts, with interpreters in 161 languages. You can call with a question, too.^1,10
• When it’s 911 instead. If the person has collapsed or won’t wake up, has severe chest pain or trouble breathing, or shows other life-threatening signs.⁶⁴
• What a GLP-1 overdose looks like. Severe nausea, severe vomiting and severe low blood sugar, says Wegovy’s label. FDA’s reports of compounded semaglutide overdoses add fainting, headache, migraine, dehydration, pancreatitis and gallstones.^7,57
• It can last for days. Semaglutide’s half-life is about a week and tirzepatide’s about 5 days, so an overdose may need watching for a long time.^7,8
• Measuring mix-ups. Confusing units, milliliters and milligrams when measuring with a syringe has led people to inject 5 to 20 times their intended dose, FDA reports.⁵⁷ How to avoid it

How do you report a side effect to FDA?

Tell your doctor first, then report it to FDA’s MedWatch program online or at 1-800-FDA-1088. It matters most for compounded products, because the pharmacies that make them often don’t have to report.

• Three ways to report. Use MedWatch’s online form, call 1-800-FDA-1088 on weekdays from 8 a.m. to 4:30 p.m. Eastern, or fax consumer form 3500B to 1-800-FDA-0178. MedWatch doesn’t give medical advice.^65,66
• Why it matters for compounded drugs. Federal law doesn’t require state-licensed pharmacies that aren’t outsourcing facilities to report problems to FDA, so it may not hear about them otherwise.^57,63

Sources

Warning signs come from FDA-approved drug labels and CDC, NIH and FDA pages; rates from the labels’ trial tables; peptide risks from FDA reviews, studies and case reports. Tap a number anywhere on this page to see its source.