Peptides 101

What a peptide actually is

A peptide is a short chain of amino acids, the same building blocks that make up proteins. Where a protein might be hundreds of amino acids long, a peptide is usually somewhere between two and fifty. That small size is the point: peptides act as messengers, carrying a specific instruction to a specific type of cell.

Your body already runs on them

Insulin is a peptide. So are oxytocin, growth hormone-releasing hormone, and the GLP-1 that your gut releases after a meal. Most of the compounds in the library are either copies of a natural signalling peptide, fragments of one, or tweaked versions designed to last longer in the bloodstream.

Why they are usually injected

Peptides are digested like any other protein, so swallowing most of them breaks the message apart before it reaches the blood. A small subcutaneous injection into the fatty layer under the skin bypasses digestion. A few, like BPC-157, are also studied orally because they are unusually stable.

The main families

How to read a dosing line

Peptides arrive as a freeze-dried powder in a small vial, labelled by total weight in milligrams. Before use the powder is dissolved in bacteriostatic water. The amount of water you add sets the concentration, and the concentration is what converts a dose in micrograms into a mark on the syringe.

Standard insulin syringes are marked in units, where 100 units is one millilitre. So a 10-unit draw is 0.1 mL. The calculator handles the conversion, and the guide walks through the physical steps.

Cycles and titration

Most research protocols run for a set number of weeks and then pause. The pause matters for compounds that act on receptors, which can become less responsive with continuous exposure. Metabolic peptides like Tirzepatide are instead titrated: the starting dose is deliberately low and stepped up over weeks to let the gut adapt.