What Are Peptides? A Plain-English Guide to Peptide Therapy

Peptides, proteins, and drugs

Every protein in your body is a chain of amino acids folded into a shape. A peptide is the same thing, just short — by convention, fewer than about fifty amino acids. Insulin is a peptide. So are oxytocin, the hormone released during labor and bonding, and GLP-1, the gut hormone that tells your brain you have eaten.

That size puts peptides in an interesting middle ground. Small-molecule drugs (aspirin, statins) are tiny and can be swallowed as pills, but they tend to touch many targets at once. Full proteins (antibodies, growth hormone) are large and precise but expensive to make and fragile. Peptides are precise like proteins — each one fits a specific receptor — but simple enough to synthesize reliably, which is why more than eighty peptide drugs have reached the market and hundreds more are in trials (Wang 2022).

The trade-off is delivery. Peptides are digested like food, so with rare exceptions they cannot be taken as pills. Almost every peptide in this guide is injected under the skin with an insulin syringe, once a day or once a week.

How peptide therapy works

A therapeutic peptide is either an exact copy of a signal your body already makes, or a modified version of one — an analog — engineered to last longer or bind more tightly.

• Semaglutide is an analog of GLP-1 with two changes that stretch its half-life from minutes to a week.
• Sermorelin is the first 29 amino acids of growth-hormone-releasing hormone, enough to trigger the pituitary.
• BPC-157 is a fragment of a protein found in gastric juice, studied for its role in tissue repair.

In each case the peptide is not adding a foreign substance so much as turning up a signal the body already uses. That is why peptide side effects tend to be extensions of the signal itself: a GLP-1 analog slows digestion (nausea), a growth-hormone secretagogue can cause water retention, and so on.

Where peptides come from

Injectable peptides for human use are made in one of two ways:

1. Branded pharmaceuticals — semaglutide as Ozempic or Wegovy, tesamorelin as Egrifta — manufactured under FDA approval for a specific indication.
2. Compounded medications — the same or related molecules prepared by a licensed compounding pharmacy for an individual patient, under a prescription. Most of the peptides in this guide are available only this way.

A third category exists online: vials labelled "for research use only." These are sold without a prescription and are not manufactured, tested, or labelled for human use. The legal and purchasing topic in this guide covers why that distinction matters.

What peptides are used for

The peptides in this guide fall into a handful of families:

Each family has its own section in this guide, and every compound has a dosage calculator that turns a prescribed dose into a syringe measurement.

What to expect as a patient

Peptide therapy is a prescription, so the process starts with a provider, not a checkout page:

1. Consultation — a video visit covering your goals, history, and current medications.
2. Prescription — if appropriate, the provider writes for a specific peptide, dose, and duration.
3. Delivery — the pharmacy compounds it and ships it cold-chain; you reconstitute the vial at home.
4. Follow-up — doses are adjusted based on how you respond, and refills are approved by the provider.

The rest of this guide walks through each of those steps in detail, starting with the practical skills — reconstituting a vial and giving a subcutaneous injection.

FREQUENTLY ASKED

SOURCES

1. Wang L, et al. Therapeutic peptides — current applications and future directions. Signal Transduction and Targeted Therapy (2022)
2. Lau JL, Dunn MK. Therapeutic peptides — historical perspectives, current development trends, and future directions. Bioorganic & Medicinal Chemistry (2018)