Peptides: Their Uses and Misuses

You may have heard about peptides lately: from a wellness influencer online or your friend at the gym. The purported benefits of taking peptides are wide-ranging: more muscle, less fat, better memory, quicker wound healing and healthier skin. But what are they? And are they safe? Can they really do what their promoters claim?

What are peptides? Peptides are short chains of amino acids — basically fragments of proteins. They occur naturally in the body, and we also make them by breaking down the food we eat.  While they are closely related to proteins, peptides are smaller and typically consist of between two and about fifty amino acids. This relatively simple structure allows peptides to act as highly specific signaling molecules in the body, regulating processes such as metabolism, immune response, tissue repair, and cell communication. Many different naturally occurring peptides are found in all living organisms. In humans, thousands of peptides have been identified, many of which function as hormones, neurotransmitters, or immune modulators. Examples include leptin, which helps regulate appetite, and endorphins, which help control pain perception.

A peptide is formed when amino acids are linked together through peptide bonds. Amino acids themselves are the fundamental building blocks of proteins, but peptides differ from proteins mainly in size and structural complexity. While proteins often fold into complex three-dimensional shapes, peptides are generally much smaller and more flexible, allowing them to interact precisely with specific receptors in the body. This specificity is one of the main reasons peptides are so valuable in biological applications.  They help digestion, trigger ovulation, regulate blood pressure, and more. Insulin, the hormone that helps the body process sugar in the blood, is a peptide. In the same way as scientists have made insulin, some peptides have been synthesized outside the body and turned into medications. The latest class of diabetes and weight-loss drugs, GLP-1s such as Ozempic and Zepbound, are peptides. Other peptides, such as collagen peptides, can be taken orally and sold over the counter alongside vitamins and dietary supplements.

Peptides are primarily involved in cell signaling. They act as chemical messengers that bind to specific receptors on the surface of target cells, triggering a cascade of biological responses. Different peptides can trigger the release of hormones, activate of immune defenses, or stimulate cell growth and repair. In contrast to chemical drugs, which often trigger unwanted reactions in the body, causing unpleasant side-effects, peptides are highly selective in their actions. They can regulate complex physiological processes with minimal unintended effects. Peptides also play a role in the body’s innate defense mechanisms. Antimicrobial peptides, for example, can directly destroy bacteria, fungi, and some viruses by disrupting their cell membranes. This function makes them an important area of research in the fight against antibiotic-resistant infections.

Federally approved peptide medications are meant to treat specific conditions, but physicians can prescribe them off-label to treat other conditions, as was the case with diabetes drugs now used for weight loss.  But even if they are being used off-label, approved peptides have been tested for safety in clinical trials. The same is not true for numerous peptides being used by athletes and advertised by wellness influencers. A vast majority of these non-approved peptides are injected. These injectable peptides, many of which have Star Wars droid-like names, have a wide range of purported benefits. Some are said to improve muscle mass, cognition, and sleep by stimulating the production of human growth hormone. Others are promoted for muscle and tissue healing. Some people recommend taking them together, as a peptide cocktail. These are just a few of the growing peptide options on the market, several of which are banned for professional athletes by the World Anti-Doping Agency.

Most of the safety and efficacy evidence for these peptides comes from studies in animals — not humans. The lack of clinical data in humans makes it challenging to figure out benefit, appropriate dosing, and unintended side effects. Long-term safety risks are completely unknown!

Like GLP-1s, some of these medications may one day be approved therapeutics, but currently, evidence is limited. A gray market has emerged with online retailers marketing peptides for human health, without safety or efficacy studies. That hasn't stopped online shoppers from buying and self-administering various peptides! Beyond peptides' unknown safety profiles, getting injectable medications online comes with great uncertainty and risk. Independent labs have found that what is being advertised isn't always what buyers receive.

Peptides as medicine have huge potential, and much research is ongoing about their applications for human health. However, as we write this, many possible long-term effects are not known. Our bodies’ own natural peptides are broken down in minutes, but synthetic drug peptides persist in the body for much longer. It makes sense to us that if a biologically active substance is amping up cell signalling, it’s important to understand just what message you are amping up.