Receptor targets
Semaglutide is a GLP-1 receptor agonist. It acts on the receptor for glucagon-like peptide-1, a hormone involved in glucose regulation and appetite signaling.
Tirzepatide is a dual agonist. It acts on the GLP-1 receptor and additionally on the GIP receptor — glucose-dependent insulinotropic polypeptide — giving it a second mechanism.
Retatrutide, still under clinical investigation, extends this further by adding glucagon-receptor activity. It is not an approved medication.
What that means practically
Both are prescription-only and are typically administered as weekly subcutaneous injections, with dosing titrated upward gradually under provider supervision.
Titration exists to manage tolerability. The schedule is set by the prescribing provider based on individual response, not by a fixed rule.
Why a provider is not optional here
These medications interact with other conditions and medications, are not appropriate for everyone, and require monitoring. They also carry contraindications that only a clinical review can identify.
Any seller offering either compound without a prescription and a provider assessment is not operating within the regulated channel — regardless of how the product is labeled.
Availability changes
The compounding status of GLP-1 medications has shifted repeatedly in recent years alongside shortage designations and regulatory action.
What is available through a compounding pathway at any given moment is determined by current rules and by your provider — not by what a vendor advertises.