An Active Pharmaceutical Ingredient is the substance in a drug product responsible for its physiological effect — the compound itself, before it is incorporated into a finished dosage form.
In compounding, the API is the starting material. A 503A pharmacy purchases APIs from suppliers, then combines them with excipients, solvents, and a delivery format — oral, topical, sterile injectable — to produce a patient-specific compounded preparation under a valid prescription.
The finished compounded drug is the regulated product. The API is one of its inputs. Documentation moves with the API: identity, purity, source, and storage conditions are recorded so the downstream compounder can satisfy state board and USP requirements.
APIs sold to 503A pharmacies by US Peptide Clinic are not finished drugs. They are starting materials. The COA covers identity, purity, and storage; the pharmacy retains all responsibility for compounding under USP <797> or <795>, state board recordkeeping, and patient-specific dispensing.