What exactly are peptides?

Peptides are short chains of amino acids (typically between 2 and 50) linked together by peptide bonds. Think of amino acids as individual Lego bricks. When you snap a few together, you get a peptide. Snap hundreds or thousands together, and you get a protein. Your body produces thousands of peptides naturally. They act as signaling molecules, telling your cells what to do.

Scientists first identified peptides in the early 20th century, but therapeutic applications have exploded in recent decades. Insulin, one of the earliest peptide therapies, has been used since the 1920s to treat diabetes. Today, more than 80 peptide drugs have been approved worldwide, with hundreds more in clinical trials.

Peptides vs. proteins vs. hormones

Feature Peptides Proteins Hormones
Size 2-50 amino acids 50+ amino acids Varies (can be peptides, proteins, or steroids)
Structure Simple chains, sometimes cyclic Complex 3D folded structures Depends on type
Examples BPC-157, GHK-Cu Collagen, hemoglobin Insulin (peptide), testosterone (steroid)
Function Signaling, modulation Structural, enzymatic, transport Systemic regulation

Some hormones are peptides. Insulin is a peptide hormone. So is oxytocin. But not all hormones are peptides. Testosterone and estrogen are steroid hormones built from cholesterol, not amino acids.

Common categories of therapeutic peptides

GLP-1 receptor agonists

GLP-1 receptor agonists mimic a natural gut hormone that regulates blood sugar and appetite. This category has gotten enormous mainstream attention thanks to semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound). Semaglutide demonstrated average weight loss of about 15% of body weight in the STEP 1 trial.

Growth hormone secretagogues

These peptides stimulate your pituitary gland to produce and release more growth hormone. Unlike synthetic HGH, they work with your body's natural feedback loops. Popular examples include ipamorelin, CJC-1295, and tesamorelin.

Healing and recovery peptides

BPC-157 is the most discussed peptide in this category. Derived from a protein found in gastric juice, it has shown strong tissue-healing properties in animal studies. TB-500 (thymosin beta-4) is another recovery peptide studied for wound healing and tissue repair.

Skin and anti-aging peptides

GHK-Cu (copper peptide) is a naturally occurring tripeptide that declines with age. Research suggests it promotes collagen synthesis, has anti-inflammatory effects, and may support wound healing and skin remodeling.

Cognitive and nootropic peptides

Selank and semax are synthetic peptides developed at the Institute of Molecular Genetics in Russia. Both are approved as medications in Russia but are not FDA-approved in the United States.

How peptide therapy works: routes of administration

  • Subcutaneous injection: The most common route. A small needle injects the peptide into the fat layer just under the skin. Most GLP-1 agonists, growth hormone secretagogues, and healing peptides use this method.
  • Oral administration: Historically difficult because stomach acid destroys peptides. Advances like oral semaglutide (Rybelsus) use absorption enhancers to protect the peptide.
  • Nasal spray: Some peptides are absorbed well through the nasal mucosa. Selank and semax are commonly administered this way.
  • Topical application: Peptides like GHK-Cu are applied directly to the skin in creams and serums for localized effects.

FDA-approved vs. research peptides

Several peptide therapies have gone through full clinical trials and received FDA approval, including semaglutide and tesamorelin. When a peptide is FDA-approved, it has been rigorously tested for safety and efficacy in human trials and is manufactured to pharmaceutical-grade standards.

Many popular peptides (BPC-157, ipamorelin, CJC-1295, TB-500) exist in a regulatory gray area. They're sold as "research chemicals" not intended for human consumption. In 2023, the FDA issued warning letters to several compounding pharmacies and took steps to restrict certain peptides being marketed without approval.

Quality matters: Research peptides are not manufactured under the same strict controls as FDA-approved drugs. Third-party testing has found that some peptide products contain incorrect doses, contaminants, or entirely different compounds. If you choose to use research peptides, seek out suppliers that provide certificates of analysis from independent labs.

Safety considerations

  • Injection site reactions: Redness, swelling, or itching at the injection site is the most common side effect across nearly all injectable peptides.
  • GI issues: GLP-1 agonists like semaglutide frequently cause nausea, vomiting, and diarrhea, especially when starting therapy.
  • Hormonal effects: Growth hormone secretagogues can cause water retention, joint pain, numbness, and tingling.
  • Unknown long-term risks: For many research peptides, we simply don't have long-term human safety data.

How to evaluate peptide research

  • Check the study type. Randomized controlled trials (RCTs) in humans are the gold standard. Animal studies don't reliably translate to humans.
  • Look at sample size. A study with 10 participants tells you much less than one with 1,000.
  • Consider the source. Was it published in a peer-reviewed journal? Is the journal reputable?
  • Watch for conflicts of interest. Was the study funded by a peptide manufacturer?
  • Look for replication. Has the finding been reproduced by independent groups?

Talk to a healthcare provider: This guide is for educational purposes only and is not medical advice. Peptide therapy should be pursued under the guidance of a qualified healthcare provider who can evaluate your individual health status, screen for contraindications, and monitor for side effects.

Sources

  1. Muttenthaler M, et al. Therapeutic peptides: historical perspectives, current development trends, and future directions. Nature Reviews Drug Discovery. 2021;20(4):309-325.
  2. Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med. 2021;384(11):989-1002.
  3. Sikiric P, et al. Stable gastric pentadecapeptide BPC 157: novel therapy in gastrointestinal tract. Current Pharmaceutical Design. 2011;17(16):1612-1632.
  4. Pickart L, et al. GHK peptide as a natural modulator of multiple cellular pathways in skin regeneration. BioMed Research International. 2015;2015:648108.
  5. Ghigo E, et al. Growth hormone secretagogues: history, mechanism of action, and clinical development. J Endocrinol Invest. 1997;20(7):432-444.
  6. Lau JL, Dunn MK. Therapeutic peptides: current status and future directions. Bioorganic & Medicinal Chemistry. 2018;26(10):2700-2707.