What is Semaglutide made of?
A familiar gut hormone, carefully altered. The small substitutions are the interesting part.
Semaglutide peptide
Semaglutide is a synthetic analogue of GLP-1, the gut hormone released after food. Its chain shares approximately 94% structural similarity with human GLP-1. The resemblance lets it activate the same receptor; the alterations help it survive long enough to serve as a medicine.
I enjoy that combination of familiarity and deliberate alteration. Calling the molecule synthetic gives only the beginning of its description. The useful questions concern which building blocks were changed, what those changes accomplish, and what happens when the resulting signal persists.
Natural GLP-1 is cleared within about two minutes. Semaglutide has an elimination half-life of approximately one week: the time it takes the amount in circulation to fall by half. That difference underlies the weekly injection form. Its molecular formula, C187H291N45O59, identifies a particular substance; it cannot express the full clinical experience of receiving it.
What makes Semaglutide last longer
An enzyme called DPP-4 rapidly breaks down natural GLP-1. In semaglutide, alpha-aminoisobutyric acid replaces alanine at position 8, protecting the chain against that cleavage. At position 34, arginine replaces lysine. A C18 fatty di-acid side chain is attached at the remaining lysine at position 26; its reversible binding to albumin, a blood protein, slows clearance and metabolism.
The distinction matters: the position-8 substitution supplies resistance to DPP-4, while the fatty side chain supplies albumin binding. I prefer the actual alterations to the vague assurance that a molecule has been improved. Here the improvement has a physical description.
That persistence also outlasts a decision to stop. Semaglutide remains in circulation for roughly five weeks after the final dose. The same construction that permits a long interval between injections helps explain why the effects of a change cannot be assumed to end overnight.
Chemistry explains why the molecule lasts; it does not decide who should use it. At mypromise.com, Promise Peptides prescribes semaglutide today after an individual assessment; the decision belongs to its clinician, licensed in the U.S. Its clinicians can refuse a prescription; its care reaches patients within the U.S., with options set by the patient's state and the treatment under consideration. Semaglutide has FDA-approved products; compounding creates a preparation with no FDA approval.
How does Semaglutide work?
GLP-1 receptor activation increases insulin secretion when glucose rises and suppresses inappropriate glucagon release; glucagon is a hormone that helps raise blood sugar. Semaglutide also slows stomach emptying. The safety review discusses the stomach and bowel effects alongside the medicine's clinical benefits.
Appetite brings the brain into the account. Semaglutide reached appetite-related brainstem and hypothalamic regions in mice and rats, where food intake fell and food preference changed without reduced energy expenditure. Earlier mouse work with liraglutide examined the arcuate nucleus, an appetite-related region. That earlier experiment concerns another GLP-1 receptor agonist, and provides background for the later semaglutide work.
The appetite pathway displaced my picture of a chemical somehow dissolving body fat. The observations concern eating, signaling and whole-body changes. The body-composition substudy then asks which tissues accounted for the weight lost.
Semaglutide formulations
The weekly subcutaneous injection places semaglutide beneath the skin. The daily oral tablet has an additional problem to solve: passage through the stomach wall. SNAC, its absorption enhancer, temporarily changes local conditions so a small share of the peptide can reach circulation. The oral formulation review reports bioavailability of about 0.4–1%.
Approved uses include type 2 diabetes, chronic weight management and certain cardiovascular risk reductions. The current indication history also includes a 2025 approval for a form used in MASH, a fatty liver illness with inflammation. Approval concerns particular products and indications; a compounded version of semaglutide has no FDA approval.
The organ trials and study doses separate these questions more usefully than a single list of things semaglutide does. The molecule's construction impresses me, especially at the point where its neat chemistry encounters a complicated body.