503A Compounding

503A Compounding

Section 503A of the Federal Food, Drug, and Cosmetic Act covers state-licensed pharmacies that compound drugs for named individual patients with a valid prescription. 503A compounding is exempt from some FDA rules that apply to commercially made drugs, most notably new-drug approval, the full cGMP manufacturing standards and labeling rules. In return, the conditions are strict. The drug must be compounded for a specific patient. The bulk drug substance must be on an FDA-approved list or meet specific qualifying criteria. And the pharmacy must work under the oversight of its state board of pharmacy.

The related section 503B covers “outsourcing facilities.” These registered facilities may compound drugs without individual prescriptions, but they must meet requirements closer to cGMP and accept FDA inspection.

Neither 503A nor 503B compounding is legal for investigational compounds such as retatrutide. For compounding to be legal, the bulk drug substance must be on an applicable FDA-approved list (or meet specific monograph or listing criteria), and retatrutide does not qualify. It is investigational. It has never been FDA-approved. It has never been on the FDA drug shortage list (the temporary route that briefly allowed semaglutide and tirzepatide to be compounded). And it has no applicable USP or NF monograph.

The FDA has acted on this. In September 2025 it sent more than fifty warning letters to compounders selling products labeled as retatrutide. In December 2025 it sent a warning letter to Darmerica, an importer of active pharmaceutical ingredients, citing cGMP violations, distribution to 503A compounding pharmacies and failure to list all drugs it shipped across state lines. The legal and safety upshot: any product sold as retatrutide outside an authorized clinical trial is unapproved, is not made under the controls that apply to approved drugs, and may not even contain the active ingredient it claims.