What are peptides? A plain-language guide

Think of peptides as instructions for cells. Your body makes thousands of them, and each one carries a message: release this, store that, slow down, speed up. Insulin is a peptide. GLP-1, the gut hormone that tells your body you've eaten, is a peptide. So are many of the medicines built to copy those messages. It's a very broad category, which is why "peptide" on its own tells you little until you know which one you're talking about.

What is a peptide?

The chemistry, briefly. A peptide is a short chain of amino acids joined end to end. Amino acids are the small molecules your body uses to build proteins, and the link between two of them is called a peptide bond. Chemists call a chain a peptide while it's short and a protein once it's long, and they draw that line in slightly different places, often somewhere around 50 amino acids. We asked Dr. Humaira Ali how she explains it to a friend.

"A short chain of amino acids that acts as a signal. I think of a peptide as a text message running through your body, telling other cells what to do: ramp this up, dial that down."

How are peptides different from proteins?

Both are made of amino acids. Peptides are shorter chains. Proteins are longer chains that fold into shapes, and the shape is what lets a protein do complex work, like carrying oxygen or speeding up a chemical reaction. The word "polypeptide" sits in between: a long chain that hasn't folded into a working protein.

What do peptides do in the body?

Mostly, they carry messages. One organ releases a peptide into the blood, and cells elsewhere pick up the signal: insulin and GLP-1 work this way, and so do other hormones you've heard of. Other peptides help with digestion or form part of the immune system's defenses. That messenger role is why peptides interest medicine: a medicine built to resemble a natural signal can be made to carry a signal of its own.

What are peptides used for?

Peptides turn up in three places: in medicines, in skin care, and in the lab. Peptide medicines go back about a century, to the first insulin injections of the 1920s, and dozens are approved today.

What is peptide therapy?

"Peptide therapy" isn't one treatment. It's the general name for being prescribed a peptide medicine by a clinician for a specific goal, usually as an injection you give yourself at home, with the clinician following up. Which peptide, what dose and for how long are the prescriber's decisions, made for you. This guide doesn't recommend any product.

Are peptides steroids?

No. Peptides are chains of amino acids; steroids are a different class of molecule built on a ring-shaped carbon structure. Dr. Ali is blunter.

"No. Completely different drug classes, different mechanisms, a very different evidence base. That goes for anabolic steroids and for the anti-inflammatory kind."

If you compete in a sport, check the World Anti-Doping Agency's current list before starting any prescription, because some peptides are on it.

What about collagen peptides?

Collagen peptides are a different thing again. They're a supplement: collagen from animal sources broken into short chains so it dissolves in a drink. They're sold as food, not medicine, so they don't need a prescription and FDA doesn't review them before sale. They're not the peptides a prescriber prescribes, and this guide doesn't weigh the evidence on supplements.

What do peptides do in skin care?

In skin care, peptides are ingredients in creams and serums. A product that says it improves how skin looks is sold as a cosmetic. A product that claims to change how skin works would be regulated as a drug, and FDA decides which is which by what the product is meant to do. "Cosmeceutical" sounds official, but FDA says the word has no legal meaning. A prescription medicine and a face cream can both list peptides on the label and have little else in common. Dr. Ali's shortcut skips the chemistry.

"A peptide in a cream is still a peptide, it just doesn't get into you the same way. The better question is: do I need a prescription for this? If yes, there's a specific dose and real oversight behind it. If no, someone put the word peptide on a label."

Is NAD+ a peptide?

No. NAD+ is a coenzyme, a molecule your cells use in energy metabolism, not a chain of amino acids. It often gets grouped with peptides because it's also a prescription injection.

Are peptides legal?

Yes, with a prescription. Approved peptide medicines and compounded peptide prescriptions are both prescription drugs: a licensed clinician writes the prescription and a licensed pharmacy fills it. Skin care peptides and collagen supplements are sold over the counter. Where people run into trouble is buying prescription-only peptides without a prescription, or from a seller that isn't a licensed pharmacy. That includes vials sold online "for research use only": being able to buy one, even with a certificate of analysis, doesn't make it approved or safe for people.

FDA approves finished medicines after reviewing the manufacturer's evidence that they're safe and effective. Compounded medications don't go through that review. Most are prepared by a traditional compounding pharmacy (called a 503A pharmacy) for an individual's prescription and are overseen mainly by state pharmacy boards. Others come from FDA-registered outsourcing facilities (called 503B facilities), which can make larger batches and must meet federal manufacturing standards. Either way, the medication itself isn't FDA-approved, so responsibility rests with the prescriber who orders it and the pharmacy that prepares it. If you'd like the longer version, read 503A vs 503B: what it means for your prescription.

How do you get prescription peptides?

The same way you get any prescription: a clinician reviews your health history and decides whether a medicine is right for you. At The Protocole, you meet a clinician live or complete an intake on your own, a doctor reviews everything and makes the call, and if you're prescribed, the pharmacy prepares your medication and ships it to your door with an injection guide. If you're curious how the injection itself works, read How to inject peptides at home, step by step.

Are peptides safe?

It depends on which peptide, and on you. A prescription peptide is a prescription medicine, so the usual rules apply: it has side effects, listed in the information that comes with it, and it isn't right for everyone. That's why your prescriber needs your full health history, including every medicine and supplement you take, before writing anything. If something doesn't feel right after a dose, call your prescriber. Collagen supplements and skin care are a different conversation, and this guide doesn't cover them.

Before any prescription, Dr. Ali wants the conversation to start with you, not with the peptide.

"Start with your goal and your medical history. Tell your prescriber what you're already doing for the basics: how you sleep, how you exercise, how you eat, how much water you drink, how you handle stress. Then tell them what you actually want from this. A targeted goal is how you use peptides properly. These things do have side effects."