What Are Peptides?

Given claims that peptide products can help with everything from skincare to workout recovery, knowing what to believe about them can be hard. Start with the facts.

At the most basic level, peptides are short chains of amino acids, the building blocks of proteins. The human body naturally makes thousands of different peptides that help regulate many of its functions. Most peptides act like messengers, locking on to specific proteins and telling cells what to do. Peptide products made in a laboratory can work the same way.

Some peptide products are used in prescription medicines like GLP-1s (the “P” stands for peptide). Other products are marketed for different purposes. These include peptide injections offered at medical spas and peptide supplements available at stores. However, peptide products can vary widely in their use, safety, and effectiveness.

What do people use peptides for?

Some medicines containing peptides are approved by the US Food and Drug Administration (FDA) to treat diabetes and cancer. These peptide treatments have gone through several phases of clinical trials in humans to show that they are safe and effective.

Other peptide products are marketed with claims that they enhance health and wellness. Influencers and medical spas often promote them as ways to smooth wrinkles, relieve joint pain, or speed up workout recovery. Still others are marketed as dietary supplements taken orally to build muscle or improve skin, hair, and joint function. But studies supporting these claims are limited, and the FDA has not approved these uses of peptide products.

“I’m always interested in learning about new integrative or holistic therapies. Importantly, we need to demonstrate that these new treatments are safe, and that they do what they claim to do,” said Neal Shore, MD, an American Society of Clinical Oncology (ASCO) expert in urologic cancer care. Dr. Shore has been involved in more than 500 clinical trials, including peptide therapies being studied for people with cancer.

Approved peptide medicines

Peptides used in FDA-approved medicines are small and precise. They can be designed to hit a particular mark or take a certain action in the body. This allows them to work in targeted ways to treat certain medical conditions.

Peptide medicines have been approved to treat several conditions, including:

Cancer

• Some peptide-based cancer treatments block hormones that help certain tumors grow, such as some hormonal treatments for prostate cancer and breast cancer.
• Other peptides act as guides to deliver specific cancer drugs directly into cancer cells. Some neuroendocrine tumors are treated in this way.
• Clinical trials are testing cancer vaccines made with peptides designed to help the immune system recognize and attack cancer cells.

Diabetes and excess body weight

• GLP-1 receptor agonists (GLP-1s), like semaglutide, mimic the action of natural gut peptides to help control blood sugar and support weight loss.
• Insulin is a peptide medicine that replaces or acts like the natural insulin made by the body to control blood sugar. Prescribed insulin can be the same as the natural form or changed in a lab to work differently. Millions of people with diabetes use prescribed insulin.

Unapproved “wellness” peptides

Peptides like BPC-157, TB-500, and KPV are marketed for benefits such as muscle repair, gut healing, anti-aging, and more. Although some have been studied in laboratories or animals, they have not been fully tested in human studies. Studies done only on cells or animals are not the same as clinical trials in people that determine if a treatment is safe and works for a specific condition.

“Just because something sounds appealing doesn’t make it effective or safe,” said Dr. Shore.

Quality and purity of unapproved peptide products are other major concerns. These products have not been reviewed by the FDA for safety, quality, and effectiveness. As a result, they can contain harmful chemicals or bacteria.

Glutathione is one example of a peptide that’s not FDA-approved but has been marketed for wellness. It is a natural 3-amino-acid peptide mostly made by the liver to protect cells. Products containing glutathione are often promoted as supplements for benefits like detox, energy, and skin lightening. Again, these benefits have not been well studied in clinical trials.

In 2026, some glutathione products were recalled because of contamination with bacterial toxins. The FDA reported the contamination caused severe reactions in some people who used them.

Peptides and cancer risk

Current evidence from studies does not show if the use of peptides increases a person’s cancer risk. It’s also not known if using peptides can affect existing cancers. But doctors and researchers are taking both possibilities seriously.

Early laboratory tests in cells and animals suggest that some peptides may promote cell growth, repair tissue, and build new blood vessels (a process called angiogenesis). These same processes help both normal and cancer cells grow. More research is needed to determine whether this is a concern for peptide use.

Doctors are also concerned that people with cancer may want to use unapproved peptides instead of standard or traditional cancer treatments. Some peptides are marketed as “natural” or “restorative.” People may think they are safer than cancer treatments like chemotherapy, which can have harsh side effects. However, these claims about peptide products do not mean they are safe or free of side effects.

“I really worry that people are choosing these sorts of treatments instead of proven care,” said Dr. Shore. Making the choice to use unproven therapies could give the cancer time to grow and spread.

Are peptides safe?

The answer depends on the peptide and why it’s being used. If your doctor prescribes an FDA-approved peptide treatment, you can feel confident in its safety. Although they can have side effects, these medicines have been tested in thousands of people during clinical trials. Doctors know the side effects and understand how to manage them safely.

However, taking unapproved wellness peptides is risky. These products have not been evaluated by the FDA for safety or quality, and they can carry hidden contaminants. Oncologists advise people with cancer to be cautious.

“I explain to patients that I cannot endorse unapproved wellness products. I want to see the scientific evidence first, based on well-designed clinical trials,” said Dr. Shore.

Talk with your oncologist or primary care doctor before starting any new medicine or supplement containing peptides.

Learn more about cancer treatment from the American Cancer Society:

• Making Treatment Decisions
• Understanding Integrative (Holistic) Medicine
• Understanding Information About New Cancer Treatments

Dr. Shore is an ASCO member.