How Peptides Work
Lock-and-key signalling
Peptides work by binding to specific receptors on cell surfaces, kicking off a cascade inside the cell. The receptor is the lock, the peptide is the key. Precise fit = precise effect. Miss the fit = nothing happens.
Half-life is destiny
Natural GLP-1 lasts ~2 minutes in the blood before enzymes chew it up. Semaglutide is engineered to resist those enzymes and bind to albumin, stretching its half-life to ~7 days — which is why you inject it weekly instead of continuously.
Order the lifecycle
Drag these into the correct order for a subcutaneous peptide injection.
Specificity is the upside
Because a peptide's shape determines which receptor it fits, well-designed peptides have remarkably few side effects vs. small-molecule drugs — which often bind promiscuously to many receptors. Specificity is also why peptides are harder to formulate: tiny structural changes can kill the activity.
Compounded vs FDA-approved — the regulatory split
Most peptides discussed in longevity circles (BPC-157, TB-500, CJC-1295, ipamorelin, semax) are NOT FDA-approved drugs. They're sold by US compounding pharmacies under a §503A exemption that allows individualised prescription compounding. As of 2024 the FDA explicitly added several to its 'Category 2' bulk-substance list, restricting which pharmacies can compound them. The implications: quality control varies pharmacy-to-pharmacy; insurance won't cover them; a doctor with a compounding-friendly pharmacy network is needed. FDA-approved peptides (semaglutide, tirzepatide, terlipressin, octreotide) sit in a different regulatory tier with full pharmacovigilance.
Key Takeaway
Peptides are receptor-specific keys. Their half-life determines dosing schedule. Their shape determines their effect. Their fragility is why most need to be injected. And the regulatory tier (FDA-approved vs compounded) determines quality control — most longevity peptides sit in the compounded grey zone.