Can peptides cause blood clots, hair loss, diarrhea and more? Short answers
Approved and unapproved peptides are very different
FDA-approved peptides have known side effects on their labels. Most unapproved peptides were never tested enough to know.
By the Peptide Science Desk Editorial TeamFact-checked against FDA and official sources · Not yet reviewed by a licensed clinician. How we check facts
Short answer: It depends on the peptide. FDA-approved GLP-1 drugs like Wegovy and Zepbound often cause diarrhea, and their labels also list hair loss, kidney problems from dehydration and a thyroid tumor warning from rodent studies. Wegovy lowered heart attacks in a big trial. Blood clots, kidney stones, ED and acne are not listed on those labels. Unapproved peptides like BPC-157 and TB-500 were never tested well enough to know what they cause.
Can peptides cause blood clots?
- The Wegovy and Zepbound labels do not list blood clots as a side effect.
- The hCG label (a fertility hormone) lists blood clots in arteries, mostly linked to a problem called ovarian hyperstimulation during fertility treatment.
- For unapproved peptides, nobody has checked. Get emergency help for a swollen, painful leg, chest pain or sudden shortness of breath.
Can peptides cause diarrhea?
- Yes, GLP-1 drugs often do. On the Wegovy label, 30% of people had diarrhea vs 16% on placebo.
- On Zepbound, 19% to 23% (by dose) vs 8% on placebo.
- Retatrutide, not approved, caused diarrhea in 27% to 34% vs 13% on placebo in a Lilly trial.
- Diarrhea and vomiting can dry you out and hurt your kidneys. Drink fluids and tell your doctor if it does not stop.
Can peptides cause hair loss?
- Yes, it is on GLP-1 labels. Hair loss happened in 3.3% on Wegovy vs 1% on placebo, and 4% to 5% on Zepbound vs 1%.
- It is often shedding linked to fast weight loss.
Can peptides cause a heart attack?
- For Wegovy, a big trial showed the opposite. In SELECT, 17,604 adults with heart disease, heart attacks happened in 2.8% on Wegovy vs 3.8% on placebo. Wegovy is FDA approved to lower heart attack, stroke and heart death risk in these adults.
- The Wegovy and Zepbound labels say heart rate can go up a little.
- Vyleesi (PT-141) raises blood pressure for a few hours after a shot. Its label says not to use it with uncontrolled high blood pressure or known heart disease.
- MK-677 (a pill, not a peptide, and not approved) had a trial stopped early after heart failure in some patients. For most unapproved peptides, nobody knows.
Can peptides cause infertility?
- The Wegovy and Zepbound labels do not list infertility as a side effect. They do warn about pregnancy, based on animal studies.
- The Wegovy label says to stop it at least 2 months before a planned pregnancy, because it lasts long in the body. Ask your doctor first.
- Zepbound and Mounjaro can make birth control pills work less well. The label says to use a non-pill method or add a barrier method for 4 weeks after starting and after each dose increase.
- For unapproved peptides, nobody has studied fertility in people.
Can peptides cause kidney stones?
- Kidney stones are not listed on the Wegovy or Zepbound labels.
- The NIH says drinking enough fluid, mostly water, is the most important way to prevent kidney stones. Diarrhea and vomiting can make you low on fluid.
- For unapproved peptides, nobody has checked.
Can peptides cause kidney problems?
- GLP-1 labels warn about sudden kidney injury, mostly when vomiting or diarrhea dries people out. Some cases needed dialysis.
- Ozempic is also approved to lower the risk of kidney disease getting worse in adults with type 2 diabetes and chronic kidney disease.
- For unapproved peptides, nobody has checked.
Can peptides cause erectile dysfunction?
- ED is not listed on the Wegovy or Zepbound labels.
- Vyleesi (PT-141) is approved only for low sexual desire in some women before menopause. It is not approved for men or for ED.
- We found no study in people of unapproved peptides and ED.
Can peptides cause acne?
- Acne is not listed on the Wegovy or Zepbound labels.
- We found no study in people of unapproved peptides and acne. If a new rash or skin change worries you, see a doctor.
What about cancer?
- Wegovy and Zepbound have a boxed warning: they caused thyroid C-cell tumors in rodents. Nobody knows if they do that in people.
- People with a personal or family history of a thyroid cancer called MTC, or a condition called MEN 2, should not use them.
- The Egrifta SV (tesamorelin) label warns about a possible higher risk of tumors growing.
- For BPC-157, TB-500 and other unapproved peptides, no long-term studies in people checked for cancer. Unknown is not the same as safe or harmful.
The numbers in charts
Can peptides cause it? What the evidence says
10 worries people search for, checked against 2 FDA labels and the research on unapproved peptides
- On the label (side effect or warning)
- A big trial found LOWER risk
- Not listed on the label
- Never properly tested: unknown
- 1 GLP-1: Wegovy (semaglutide) label
- 2 GLP-1: Zepbound (tirzepatide) label
- 3 Unapproved peptides (BPC-157, TB-500, CJC-1295 and others)
| Worry | 1 | 2 | 3 |
|---|---|---|---|
| Cancerthyroid tumors in rodents | !GLP-1: Wegovy (semaglutide) label: On the label (side effect or warning) | !GLP-1: Zepbound (tirzepatide) label: On the label (side effect or warning) | ?Unapproved peptides (BPC-157, TB-500, CJC-1295 and others): Never properly tested: unknown |
| Blood clots | ·GLP-1: Wegovy (semaglutide) label: Not listed on the label | ·GLP-1: Zepbound (tirzepatide) label: Not listed on the label | ?Unapproved peptides (BPC-157, TB-500, CJC-1295 and others): Never properly tested: unknown |
| Diarrhea | !GLP-1: Wegovy (semaglutide) label: On the label (side effect or warning) | !GLP-1: Zepbound (tirzepatide) label: On the label (side effect or warning) | ?Unapproved peptides (BPC-157, TB-500, CJC-1295 and others): Never properly tested: unknown |
| Hair loss | !GLP-1: Wegovy (semaglutide) label: On the label (side effect or warning) | !GLP-1: Zepbound (tirzepatide) label: On the label (side effect or warning) | ?Unapproved peptides (BPC-157, TB-500, CJC-1295 and others): Never properly tested: unknown |
| Heart attack | ↓GLP-1: Wegovy (semaglutide) label: A big trial found LOWER risk | ·GLP-1: Zepbound (tirzepatide) label: Not listed on the label | ?Unapproved peptides (BPC-157, TB-500, CJC-1295 and others): Never properly tested: unknown |
| Infertilitypregnancy cautions | !GLP-1: Wegovy (semaglutide) label: On the label (side effect or warning) | !GLP-1: Zepbound (tirzepatide) label: On the label (side effect or warning) | ?Unapproved peptides (BPC-157, TB-500, CJC-1295 and others): Never properly tested: unknown |
| Kidney stones | ·GLP-1: Wegovy (semaglutide) label: Not listed on the label | ·GLP-1: Zepbound (tirzepatide) label: Not listed on the label | ?Unapproved peptides (BPC-157, TB-500, CJC-1295 and others): Never properly tested: unknown |
| Erectile dysfunctionED | ·GLP-1: Wegovy (semaglutide) label: Not listed on the label | ·GLP-1: Zepbound (tirzepatide) label: Not listed on the label | ?Unapproved peptides (BPC-157, TB-500, CJC-1295 and others): Never properly tested: unknown |
| Acne | ·GLP-1: Wegovy (semaglutide) label: Not listed on the label | ·GLP-1: Zepbound (tirzepatide) label: Not listed on the label | ?Unapproved peptides (BPC-157, TB-500, CJC-1295 and others): Never properly tested: unknown |
| Kidney problemsfrom dehydration | !GLP-1: Wegovy (semaglutide) label: On the label (side effect or warning) | !GLP-1: Zepbound (tirzepatide) label: On the label (side effect or warning) | ?Unapproved peptides (BPC-157, TB-500, CJC-1295 and others): Never properly tested: unknown |
"Not listed" means the label does not name it as a side effect. It is not a promise that it can never happen. "?" means nobody has measured it, not that it is safe or harmful.
Diarrhea is the most common "can it cause" answer that is a yes
Share of people with diarrhea in the main trials, drug vs placebo
GLP-1: Wegovysemaglutide, FDA label
30%
16%
GLP-1: Zepboundtirzepatide, FDA label (highest dose)
23%
8%
Retatrutidenot approvednot approved; TRIUMPH-2, Lilly (highest dose)
34%
13%
Zepbound by dose: 19%, 21% and 23% vs 8% on placebo. Retatrutide numbers are from a Lilly news release, not an FDA label.
Show the numbers as a table
| Drug (source) | On the drug | On placebo |
|---|---|---|
| GLP-1: Wegovy semaglutide, FDA label | 30% | 16% |
| GLP-1: Zepbound tirzepatide, FDA label (highest dose) | 23% | 8% |
| Retatrutide (not approved) not approved; TRIUMPH-2, Lilly (highest dose) | 34% | 13% |
Where these answers come from
| Study type | People | Main finding | Limits |
|---|---|---|---|
| FDA label: Wegovy (June 2026) | Thousands in trials | Diarrhea 30% vs 16%; hair loss 3.3% vs 1%; thyroid tumor warning (rodents) | Trial people may differ from you |
| FDA label: Zepbound (Aug 2026) | Thousands in trials | Diarrhea 19-23% vs 8%; hair loss 4-5% vs 1% | Paid for by the maker |
| Randomized trial (SELECT) | 17,604 | Heart attacks 2.8% on Wegovy vs 3.8% on placebo | Only adults who already had heart disease |
| Review of unregulated peptides, 2026 | Review | Lists risks of unregulated peptide products | Review, not a trial |
FAQ
Do peptides have side effects?
Yes. Approved peptide drugs have side effects listed on their labels. Unapproved peptides may too, but nobody measured them well.
Is "not on the label" the same as "can't happen"?
No. It means it was not seen often enough in trials to list. Report anything new to your doctor and to FDA MedWatch.
Can collagen peptides cause these problems?
Collagen peptides are a food supplement. The FDA does not approve supplements before they are sold, and we did not check them here.
Where can I report a side effect?
To FDA MedWatch at 1-800-FDA-1088 or fda.gov/medwatch.
Can peptides cause weight gain?
GLP-1 drugs cause weight loss. Weight often comes back after people stop them.
Related pages
- GLP-1: Wegovy / Ozempic (semaglutide)FDA approved · Proof: Strong
- GLP-1: Zepbound / Mounjaro (tirzepatide)FDA approved · Proof: Strong
- GLP-1: RetatrutideIn testing · Proof: Strong
- BPC-157Not approved · Proof: Early
- TB-500Not approved · Proof: Animal or lab only
- CJC-1295Not approved · Proof: Early
- Egrifta (tesamorelin)FDA approved · Proof: Strong
- Vyleesi (bremelanotide, PT-141)FDA approved · Proof: Some
- MK-677 (ibutamoren)Not approved · Proof: Mixed
- Can peptides cause cancer? What doctors actually knowGuide
- Peptide side effects: what is common and what is serious?Guide
- GLP-1 side effects: the full list, and how common each one isGuide
- GLP-1 hair loss: how common is it, and does it grow back?Guide
- Can peptides make you infertile?Guide
- Are Peptides Safe? What to Know FirstGuide
- Peptide injection site reaction: red, itchy or a lump. When to worryGuide
- Peptides for loose skin after weight loss: does GHK-Cu work?Guide
- Peptide side effects checkerTool
- Peptide drug interaction checkerTool
- How long do peptides take to work?Tool
- Compare GLP-1: Wegovy / Ozempic vs GLP-1: Zepbound / MounjaroComparison tool
We never share doses or tell you where to buy. Always ask your doctor. Print our doctor questions sheet.
Sources
- DailyMed (FDA label): Wegovy (semaglutide) prescribing information, June 2026
- DailyMed (FDA label): Zepbound (tirzepatide) prescribing information, Aug 2026
- DailyMed (FDA label): Ozempic (semaglutide) injection prescribing information, June 2026
- DailyMed (FDA label): Vyleesi (bremelanotide) prescribing information
- DailyMed (FDA label): Egrifta SV (tesamorelin) prescribing information
- DailyMed (FDA label): Chorionic gonadotropin for injection prescribing information
- PubMed: Lincoff et al., Semaglutide and cardiovascular outcomes in obesity without diabetes (SELECT), NEJM 2023
- Eli Lilly news release: retatrutide TRIUMPH-2 and TRIUMPH-3 results (July 23, 2026)
- NIDDK (NIH): Eating, diet and nutrition for kidney stones
- FDA: Bulk drug substances that may present significant safety risks
- PubMed: Review of unregulated peptide use and risks, Mo Med 2026