What GLP-1 actually is
GLP-1, short for glucagon-like peptide-1, is a hormone your gut releases after you eat. It tells your pancreas to release insulin, slows how fast food leaves your stomach, and signals your brain that you’re full. Drugs in this class copy that hormone’s effect, lasting far longer than the natural version, which breaks down within minutes.
Retatrutide and tirzepatide go further. Tirzepatide also activates the GIP receptor, and retatrutide activates GIP and glucagon receptors on top of GLP-1. Each is a peptide chain, which is exactly why it needs mixing before use rather than arriving ready to inject.
Why lyophilised, not liquid
Peptides are more stable as a freeze-dried powder than as a liquid, so most research-grade retatrutide and tirzepatide ships lyophilised. That stability is the whole reason reconstitution, mixing the powder with water, exists as a separate step rather than the product simply arriving pre-mixed.
From powder to a measurable dose
Reconstitution turns a vial of powder into a liquid with a known concentration, which is what makes it possible to draw an exact dose with a syringe. The ratio of water to powder determines that concentration, and getting the ratio right is what everything else in dosing depends on.
Why the ratio, not just “add water”, matters
Two vials with identical mg content, mixed with different amounts of water, produce solutions with different concentrations. The same syringe draw of each would deliver two different doses. This is why a specific, known ratio matters more than just “enough water to dissolve it.”
The takeaway
Understanding how these drugs work also means understanding why the mixing step exists and why the exact ratio used isn’t a minor detail.