01 /What the incretins are
Incretins are gut peptides that signal to the pancreas in response to oral nutrient intake. The two primary incretins are glucagon like peptide 1 (GLP 1) and glucose dependent insulinotropic polypeptide (GIP). Both are released from intestinal endocrine cells, both bind G protein coupled receptors on pancreatic islet cells, and both modulate insulin secretion, glucagon secretion, gastric emptying, and central appetite signaling.
The third major hormone in the same regulatory network is glucagon, released from pancreatic alpha cells. Together GLP 1, GIP, and glucagon form an interconnected loop that researchers and pharmaceutical developers have spent two decades mapping.
02 /First generation: GLP-1 receptor agonists
Native GLP 1 has a half life of about 2 minutes; the enzyme dipeptidyl peptidase 4 (DPP 4) cleaves it almost immediately. The first generation of incretin drugs were modified GLP 1 analogs designed to resist DPP 4 cleavage and circulate longer.
Liraglutide is a 31 amino acid GLP 1 analog with a fatty acid side chain that binds albumin and extends the half life to about 13 hours, enabling once daily dosing. It is approved as a prescription medicine in regulated markets.
Semaglutide is a further modified GLP 1 analog with structural changes that extend the half life to about 165 hours (one week), enabling once weekly dosing. It is approved as a prescription medicine in regulated markets.
03 /Second generation: dual incretin agonists
Tirzepatide is a 39 amino acid peptide that binds both the GIP and GLP 1 receptors as a co agonist. It is the first commercially developed dual incretin agonist and is approved as a prescription medicine in regulated markets.
The rationale for the dual agonist approach is that GIP and GLP 1 pathways are complementary: GIP enhances insulin secretion under hyperglycemic conditions, while GLP 1 also slows gastric emptying and reduces appetite. Binding both at once produces a different signaling profile than either alone.
04 /Third generation: triple agonists
Retatrutide is a triple agonist that binds GLP 1, GIP, and glucagon receptors. It is in late stage clinical research and not yet broadly approved at the time of writing. The glucagon component adds an energy expenditure signal alongside the appetite and insulin signals from GLP 1 and GIP.
Other triple agonists and tri specific molecules are in earlier development. The category is moving quickly; the published literature in 2024 to 2025 has been particularly active.
05 /Adjacent gut peptides
PYY (3-36) is a 34 amino acid fragment of the longer Peptide YY, produced by L cells in the distal intestine. It is a selective Y2 receptor agonist studied alongside GLP 1 in appetite signaling research. Apothify lists PYY (3-36) for encyclopedia coverage in the body composition category.
Oxyntomodulin is a related gut peptide that engages both GLP 1 and glucagon receptors as a natural dual agonist. It has been studied as a parent template for several synthetic dual agonists.
06 /Why these are ELEVATED in the Apothify library
All four major synthetic incretins (Liraglutide, Semaglutide, Tirzepatide, Retatrutide) are classified ELEVATED in the Apothify library. They are presented as encyclopedia entries only with no cart, no checkout, and no price.
The reason is regulatory rather than scientific. These are approved prescription medicines in regulated markets. Selling them outside of a prescription pathway puts the seller in a category of regulatory exposure that Apothify is not in business to take. The encyclopedia listing exists so the library is comprehensive, not because the products are available for purchase.
PYY (3-36) is also ELEVATED for similar reasons; while not as broadly approved as the others, the regulatory landscape around incretin family compounds is uniformly tight.
07 /Interaction rules across the family
Semaglutide and Liraglutide are flagged as redundant (both are GLP 1 receptor agonists with overlapping mechanism). Stacking adds no research signal.
Tirzepatide, Retatrutide, Semaglutide, and Liraglutide are flagged as caution in any pairwise combination, except Semaglutide plus Liraglutide which is flagged as redundant (both are GLP-1 receptor agonists with overlapping mechanism). The pathways overlap heavily and the combinations are not studied as well as the individual compounds.
PYY (3-36) plus Semaglutide and PYY (3-36) plus Liraglutide are flagged as synergy because the satiety pathway and the GLP 1 pathway are complementary.
08 /What researchers actually study
Current research questions in this family include receptor selectivity and the role of dual or triple agonism, the durability of effect over very long acting analogs (multiweek), the central appetite pathway and how it differs across compounds, the cardiovascular and renal signaling that has emerged in clinical data, and the boundary conditions where incretin signaling stops producing useful research signal.
The peer reviewed literature on this family is large and growing fast. The Apothify pages summarize the receptor profile and the canonical comparisons; the original literature is the primary source for any specific question.
09 /How to use the Apothify entries
Read the pages for orientation and family relationships. The compare tool puts any two of these compounds side by side. The interaction matrix flags the redundant or caution rules. Because all entries are encyclopedia only, there is no cart pathway; the entries link to no products.
If you need access to one of these compounds for your research, the appropriate channel is a prescription through a licensed clinician or, for clinical research, an Investigational New Drug pathway through the FDA. Apothify does not provide either.
