Can peptides cause cancer? What doctors actually know

Short answer, by type of peptide

• GLP-1 drugs (Wegovy, Ozempic, Zepbound): FDA approved. Their labels carry a boxed warning about thyroid tumors seen in rodents. Studies in people are mixed (see below).
• Tesamorelin (Egrifta SV): FDA approved for belly fat in some people with HIV. Its label says not to use it if you have active cancer, because it raises growth hormone.
• Teriparatide (Forteo): FDA approved for weak bones. It caused bone cancer in rats, but a 15-year US study did not find more bone cancer in people. The boxed warning was removed in 2020.
• BPC-157, TB-500 and other unapproved peptides: no long-term cancer studies in people. Lab studies show some help grow new blood vessels. That is why cancer doctors are careful.
• Growth hormone boosters (CJC-1295, ipamorelin, MK-677): they raise IGF-1, a growth signal. Higher natural IGF-1 is linked to a bit more of some cancers. That is not proof these products cause cancer.

• GLP-1 side effects
• Other side effects: clots, hair loss and more

Do GLP-1 drugs like Ozempic cause thyroid cancer?

• In rats and mice, semaglutide and tirzepatide caused thyroid C-cell tumors. That is why Wegovy, Ozempic and Zepbound have a boxed warning. The labels say it is not known if they do this in people.
• A French study (2,562 people with thyroid cancer, 45,184 without) found 58% higher risk of thyroid cancer after 1 to 3 years on a GLP-1 drug.
• A study in Denmark, Norway and Sweden (145,410 GLP-1 users) did not find more thyroid cancer. About 1.3 people per 10,000 got it each year on GLP-1 drugs vs 1.5 on another diabetes pill.
• Two reviews of randomized trials (Florence, 2024 and 2025) found about 1.5 times the risk of thyroid cancer. The 2024 review says that is about 1 extra case for every 1,349 people treated for 5 years.
• So the risk, if real, looks small. Thyroid cancer is rare. More checkups on these drugs may also find more small cancers.

• GLP-1: what it is and the drugs list

Who should not take GLP-1 drugs because of cancer?

• The Wegovy and Zepbound labels say not to use them if you or a family member ever had medullary thyroid cancer (MTC), or if you have a condition called MEN 2.
• Tell your doctor about a lump in your neck, trouble swallowing, a hoarse voice or shortness of breath. The labels list these as possible signs of a thyroid tumor.
• This warning is about one rare type of thyroid cancer. It is not a warning about every cancer.

Can GLP-1 drugs lower cancer risk?

• Maybe for some cancers, but this is not proven. A big US health-record study of 1.65 million people with type 2 diabetes compared GLP-1 drugs with insulin.
• People on GLP-1 drugs had lower rates of 10 of 13 cancers linked to extra weight, like colon, liver and pancreas cancer.
• Compared with metformin, GLP-1 drugs did not lower any cancer, and kidney cancer was more common.
• A 2025 review of 50 randomized trials found no overall change in cancer risk.
• Health-record studies can show a link, not a cause. No GLP-1 drug is approved to prevent cancer.

Why do growth hormone peptides raise cancer questions?

• CJC-1295, ipamorelin, sermorelin and MK-677 (a pill, not a peptide) are sold to raise growth hormone and IGF-1.
• In a small study of healthy adults, one shot of CJC-1295 raised IGF-1 1.5 to 3 times for 9 to 11 days.
• A 2004 review in The Lancet found people with naturally high IGF-1 had a bit more prostate cancer and breast cancer before menopause.
• The Egrifta SV (tesamorelin) label says growth hormone is "a known growth factor." It says not to use it with active cancer, and to stop if cancer comes back.
• None of this proves these peptides cause cancer. It is a reason to be careful, and to ask your doctor about IGF-1 tests.

Why does BPC-157 raise cancer questions?

• A 2017 lab study found BPC-157 helped grow new blood vessels in chick eggs, in rats and in human cells.
• New blood vessels help wounds heal. Tumors also need new blood vessels to grow.
• No study in people has checked whether BPC-157 causes or speeds up cancer. Unknown is not the same as safe or harmful.
• The FDA says it has no, or only a little, safety data on BPC-157 in people.

Does a cancer warning in rats mean it happens in people?

• Not always. Teriparatide (Forteo) caused bone cancer (osteosarcoma) in rats given high doses for most of their lives.
• A 15-year US study then looked for bone cancer in people who took it. It found 3 cases, when about 4 were expected by chance.
• In 2020, the FDA label was changed and the boxed warning was removed.
• Rodent tumors are a signal to watch. Only long studies in people can show the real risk, and most unapproved peptides have none.

• Teriparatide page

What do cancer centers say?

• MSK cancer doctor Larry Norton says many wellness peptides have not been tested the right way in people.
• MSK notes that some peptides claim to reduce swelling or speed healing. Those effects could also affect cancer cells. Nobody knows for sure yet.
• MSK says people with cancer should ask their care team, not order untested products online.
• Dana-Farber cancer experts say there is very little human evidence about peptides and cancer.
• They warn that some peptides may promote blood-vessel growth or other pathways that cancer cells also use.

What about TB-500?

• KFF Health News reports that a scientist who studies TB-4 (related to TB-500) planned to screen people for early cancer first.
• He said TB-4 can help new blood vessels grow, which might also help cancers grow.
• That is a caution for research planning. It is not proof that TB-500 causes cancer in people.

Are approved peptide drugs different?

• Insulin, some cancer hormone drugs, and GLP-1 shots like Ozempic and Wegovy are peptide medicines.
• Those went through careful tests and FDA approval. That is not the same as "research" peptides sold online.

What to do

• If you have cancer now, or had cancer before, ask your cancer doctor before using any unproven peptide.
• Do not start BPC-157, TB-500, KLOW blends, or other wellness peptides on your own.
• Use our printable doctor questions sheet if you want a checklist for your visit.

What should I tell my doctor?

• Every peptide, shot or supplement you take, including "research" products.
• Any cancer you have had, and any thyroid cancer in your family.
• New lumps, a hoarse voice or trouble swallowing, if you take a GLP-1 drug.
• Ask if you need an IGF-1 blood test if you take a growth hormone peptide.

More charts: Peptides by the numbers

Studies of peptides and cancer in people

We read each study on PubMed on Oct 28, 2026. Most are about approved GLP-1 drugs. We found no long-term cancer study in people for BPC-157, TB-500 or CJC-1295.