Compounding

Compounding is the practice of a pharmacist preparing a customised medication for an individual patient — adjusting a dose, combining ingredients, removing an allergen, or making a drug that isn't commercially available. In the peptide context, compounding is what makes most research peptides available by prescription in the US before they achieve FDA drug approval. A licensed practitioner writes a prescription for a specific patient; a 503A compounding pharmacy prepares the compound from a bulk active ingredient. Two things constrain this: First, the active ingredient must be on the FDA's approved bulk substances list for 503A compounding — or under active review by the PCAC. Using an unapproved bulk substance is not permitted. Second, a compounder cannot prepare "essentially a copy" of an FDA-approved drug with an active NDA. That's why tesamorelin and bremelanotide (PT-141) cannot be compounded — Egrifta and Vyleesi both have approved equivalents. The rule exists to prevent compounding from circumventing the drug approval process. Compounding is legal and regulated. Grey-market research-chemical sites operating without prescriptions and licensed pharmacies are a different thing entirely — and the regulatory distinction is real, not just semantic.