What Are Peptides? Benefits, Side Effects and Risks to Know

Peptides are short chains of amino acids, the same building blocks that make up proteins. The body naturally produces thousands of peptides that act as signals, helping regulate processes such as metabolism, hormone activity, immune function and tissue repair.

Scientists can also create peptides for use in prescription medications, skin care products and supplements.

“Peptides are not one specific treatment or a single category of product,” says Mark Esguerra, MD, an internal medicine physician at Scripps Clinic in Carmel Valley “Some are well-studied prescription medications approved for specific conditions. Others are cosmetic ingredients, dietary supplements or experimental compounds that have very little research behind them.”

That distinction matters. A peptide serum purchased at a cosmetics store is very different from an FDA-approved injectable medication or an unapproved peptide sold online for muscle growth and injury recovery.

The safety of a peptide depends on the specific product, how it is used and whether it has been tested and approved for that purpose.

Certain prescription peptide medications have been studied in clinical trials and approved by the U.S. Food and Drug Administration. These include insulin and several medications used to treat diabetes, obesity and other medical conditions.

However, many peptides promoted by wellness clinics, fitness influencers and online retailers have not been FDA-approved. Some are labeled “for research use only” or “not for human consumption,” even though they are marketed to consumers for injection.

“Peptide is a scientific term, not a guarantee that something is safe, natural or effective,” says Dr. Esguerra. “Before putting a peptide on your skin, swallowing it or injecting it, you need to know exactly what it is, what evidence supports it and where it came from.”

Compounded medications also require careful consideration. Compounded drugs can meet an individual patient’s medical needs in certain circumstances, but they are not FDA-approved. This means the FDA does not evaluate their safety, effectiveness or quality before they are sold.

Peptides are common ingredients in anti-aging creams, moisturizers and serums. They are often promoted as a way to support collagen production, reduce the appearance of fine lines and improve skin firmness.

Some research suggests that certain topical peptides may modestly improve skin hydration, texture and the appearance of wrinkles. Results can vary depending on the type and concentration of peptide, the product’s formulation and how consistently it is used. More large-scale, independent studies are needed to determine which products provide meaningful benefits.

Topical peptide products are generally considered lower risk than injectable peptides. Possible side effects include:

• Redness
• Itching
• Dryness
• Burning or irritation
• Allergic reactions

People with sensitive skin should introduce one new product at a time and consider testing it on a small area first. Stop using the product if irritation develops.

“Peptide skin care may provide some benefit, but it should not replace the basics,” says Dr. Esguerra. “Daily broad-spectrum sunscreen, avoiding tobacco and using proven ingredients such as retinoids generally have stronger evidence for preventing or improving visible skin aging.”

A dermatologist can help patients select products based on their skin type and address persistent irritation, acne, discoloration or other concerns.

Yes. Glucagon-like peptide-1, or GLP-1, is a hormone produced naturally in the body. It helps regulate blood sugar, slows stomach emptying and influences appetite.

Prescription GLP-1 and related medications mimic these natural signals. Some people call these GLP-1 peptides, but they are prescription drugs, not wellness trends. Depending on the specific drug, FDA-approved versions may be prescribed to treat type 2 diabetes, obesity or overweight accompanied by certain health conditions. Some also have approved cardiovascular, kidney or liver-related indications.

GLP-1 medications have far more clinical evidence than most of the peptides promoted online. However, they are powerful prescription drugs and are not appropriate for everyone.

Common side effects may include:

• Nausea
• Vomiting
• Diarrhea
• Constipation
• Abdominal discomfort
• Reduced appetite

Less common but potentially serious risks can include pancreatitis, gallbladder problems, kidney injury related to dehydration, severe gastrointestinal problems and serious allergic reactions. Certain medications also carry warnings related to thyroid C-cell tumors based on animal studies and should not be used by people with specific personal or family medical histories.

People taking insulin or certain other diabetes medications may also be at increased risk for low blood sugar.

“A GLP-1 medication should be prescribed as part of an individualized treatment plan,” says Dr. Esguerra. “Patients need appropriate screening, a gradual dosing schedule when indicated and follow-up to monitor side effects, nutrition, muscle mass and overall health.”

Patients should tell their care team about all medications and supplements they take, as well as any history of pancreatitis, gallbladder disease, kidney problems, severe digestive disorders or relevant endocrine conditions.

Consumers should also be cautious about compounded or unapproved products marketed as alternatives to FDA-approved GLP-1 medications. Products obtained from unverified online sellers may contain an incorrect dose, a different ingredient or contaminants.

Peptides such as BPC-157, TB-500, CJC-1295 and ipamorelin are promoted online for increasing muscle, reducing body fat, accelerating recovery and healing injured tendons or ligaments.

The marketing claims often go well beyond the available evidence. Several of these compounds have limited or no high-quality human clinical trial data supporting their safety and effectiveness for muscle growth or injury recovery. They are not FDA-approved for these uses.

Potential risks vary by compound and may include:

• Contamination or incorrect dosing
• Injection-site infections
• Allergic or immune reactions
• Fluid retention
• Headache, dizziness or nausea
• Changes in blood sugar
• Hormonal disruption
• Joint pain or numbness
• Unintended tissue growth
• Unknown long-term health effects

Products purchased through social media or websites may not contain what the label claims. Sterility is another serious concern when a product is injected.

“The greatest concern is that people may assume an injectable peptide is safe because it is popular in fitness or wellness circles,” says Dr. Esguerra. “With many of these products, we do not have reliable human evidence, standardized dosing or good long-term safety data.”

Some performance-enhancing peptides are also prohibited in competitive sports. Athletes should verify any medication or supplement before using it.

For building or preserving muscle, proven strategies include resistance training, adequate protein, sufficient sleep and treatment of underlying medical or nutritional issues. A sports medicine physician or physical therapist can create an evidence-based recovery plan for an injury.

Use caution if a peptide product or provider:

• Promises rapid weight loss, muscle gain, anti-aging or injury healing
• Uses terms such as “miracle,” “biohack” or “research chemical”
• Sells peptide injections without a prescription
• Does not require a medical history, examination or follow-up
• Does not identify a licensed pharmacy
• Encourages “stacking” several peptides
• Claims there are no side effects
• Uses celebrity testimonials instead of clinical evidence
• Labels the product “for research use only”

A licensed medical professional should review the exact product, proposed benefit, potential side effects and alternatives before a patient uses any injectable or prescription peptide.

Talk with your primary care physician before using a peptide if you:

• Take prescription medications
• Have diabetes or another metabolic condition
• Have kidney, liver, gallbladder or pancreatic disease
• Have a history of severe digestive problems
• Are pregnant, breastfeeding or planning a pregnancy
• Are preparing for surgery or a procedure requiring sedation
• Are considering an injectable, compounded or online peptide
• Develop new or severe symptoms after starting a product

Seek immediate medical care for severe abdominal pain, persistent vomiting, trouble breathing, facial or throat swelling, fainting or signs of a serious infection.

“Bring the product name, ingredient list and a photo of the label to your appointment,” says Dr. Esguerra. “Your doctor can help you separate realistic benefits from marketing claims and identify safer, evidence-based options.”

Peptides include everything from cosmetic ingredients to important prescription medications. Some have established medical uses and strong clinical evidence. Others offer modest cosmetic benefits or remain largely experimental.

Do not assume that all peptides work the same way or carry the same risks. Avoid injectable products from unverified sellers and consult a licensed health care professional before using a peptide for weight loss, muscle growth, injury recovery or another medical purpose.