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New to Peptides · Part 1: Start here

What is a peptide, in plain words?

Lesson 12.1.1 · 4 min read · Free lesson

A peptide is a short chain of building blocks called amino acids, joined end to end like beads on a string 1. When the chain gets long and folds into a complex shape, scientists usually call it a protein instead. There is no sharp line between the two, but peptides are the short ones 1.

Your body is full of them

You don't need a lab to find peptides. Your body makes many of them every day and uses them as messengers. A peptide made in one place travels to another place and tells cells what to do 2.

The best-known example is insulin. Your pancreas makes it after a meal, and it tells your cells to take sugar out of the blood. People with diabetes who can't make enough insulin have used insulin as a medicine for about a hundred years 23.

Why companies make peptide medicines

Because peptides are the body's own kind of messenger, a peptide medicine can be very precise. It can fit one "lock" (a receptor) on a cell and leave most others alone 2. That is one reason many new medicines are peptides.

Peptides also have weak spots. Stomach acid and enzymes break most of them down, so most peptide medicines are given as shots instead of pills 2. Chemists change the chain to make it last longer in the body. Later in this course you'll meet medicines that last a whole week after one shot.

Check what you learned: take this lesson's quick quiz in the Academy. It is free.

Sources

  1. Forbes J, Krishnamurthy K. Biochemistry, Peptide. StatPearls, NCBI Bookshelf (last update 08/28/2023)
  2. Wang L, et al. Therapeutic peptides: current applications and future directions. Signal Transduct Target Ther 2022;7:48 (PMC8844085)
  3. DailyMed - HUMULIN R (insulin human) injection, prescribing information (revised 6/2023)
  4. FDA - Step 3: Clinical Research (content current as of 01/04/2018)
  5. FDA - Step 4: FDA Drug Review (content current as of 01/04/2018)
  6. FDA - Compounding Laws and Policies
  7. FDA Warning Letter - Gram Peptides (MARCS-CMS 721806), March 31, 2026
  8. FDA - Step 2: Preclinical Research (content current as of 01/04/2018)
  9. Józwiak M, Bauer M, Kamysz W, Kleczkowska P. Multifunctionality and Possible Medical Application of the BPC 157 Peptide - Literature and Patent Review. Pharmaceuticals 2025;18(2):185

All lessons in New to Peptides · Medicine, trial drug, or "research chemical"? →