The 503B Bulk Drug Substances List and the Clinical Need Standard

An outsourcing facility compounding under Section 503B does not source bulk drug substances under the same rules a 503A pharmacy uses, a distinction covered in HLA's guide to Bulk Drug Substance Sourcing and the Section 503A Lists. Section 503B of the Federal Food, Drug, and Cosmetic Act restricts outsourcing facilities to substances on the 503B Bulks List, unless the compounded drug is on FDA's drug shortage list at the time of compounding. FDA decides what belongs on that list under a clinical need standard, and on April 30, 2026 proposed excluding semaglutide, tirzepatide, and liraglutide after finding no clinical need for outsourcing facilities to compound them from bulk. A facility that keeps compounding a delisted substance is compounding an unapproved drug.

A Separate List, A Separate Test

The 503A and 503B bulk drug substance lists rest on separate statutory tests, even though both answer the same question: which substances may lawfully anchor a compounded drug. Section 503A governs state-licensed pharmacies and physicians compounding under patient-specific prescriptions. Section 503B governs registered outsourcing facilities, which compound without such prescriptions and operate under current good manufacturing practice (cGMP) obligations. An outsourcing facility cannot justify bulk compounding with a substance's 503A listing; only a 503B Bulks List listing or the shortage-list route satisfies Section 503B.

The Clinical Need Standard

FDA evaluates a nominated substance under four factors from its 2019 guidance: physical and chemical characterization; safety issues raised by compounding use; available evidence of effectiveness for a drug compounded with it; and current and historical use, including the conditions treated and the peer-reviewed literature behind it. FDA weighs those factors, with input from the Pharmacy Compounding Advisory Committee, and lists a substance only where it finds a clinical need for outsourcing facilities to compound it. The semaglutide, tirzepatide, and liraglutide proposal shows the standard in practice: FDA's position is that FDA-approved GLP-1 products already meet patient need, so outsourcing facilities no longer have a clinical need to compound the same molecules from bulk.

The Shortage List as an Alternative Basis

A substance does not need a 503B Bulks List listing for lawful bulk compounding. Section 503B also permits it when the compounded drug appears on FDA's drug shortage list at the time of compounding, regardless of the substance's listing status. That route is why large-scale GLP-1 compounding was lawful for years: semaglutide sat on the shortage list from 2022 until FDA removed it in February 2025, and tirzepatide was removed in October 2024. Once a drug leaves the shortage list, a 503B Bulks List listing is the only basis left.

Interim Categories While Nominations Are Pending

FDA's 2017 interim policy sorted nominations awaiting a 503B Bulks List decision into categories describing where FDA's review stood, not a clinical need finding. Effective January 7, 2025, FDA stopped placing new nominations into that system; a substance nominated on or after that date carries no interim enforcement position and cannot be compounded from bulk until FDA completes its evaluation. Substances already in the system's most favorable category before that date remain within the prior enforcement posture until FDA finishes evaluating them. A facility relying on a pending nomination should confirm where it sits and when it was filed.

A substance that is neither on the 503B Bulks List nor compounding a drug on FDA's shortage list has no lawful basis for bulk compounding under Section 503B, regardless of how long the facility has used it.

When a Relied-Upon Substance Is Not Listed

An outsourcing facility that finds a substance is not on the 503B Bulks List, not covered by a favorable pending nomination, and not compounding a shortage-list drug faces an immediate compliance decision. Continuing exposes the facility to an unapproved-new-drug finding and an FDA warning letter. The lawful options are narrow: stop bulk compounding that substance, confirm whether an FDA-approved version of the finished drug is available to dispense instead, or pursue nomination while monitoring the shortage list for a route back. Document the decision, especially once FDA has questioned a substance's clinical need, as it has for the GLP-1 class.

Why Early Legal Counsel Is Critical

It is critical that outsourcing facilities promptly retain experienced healthcare defense counsel upon receiving an FDA warning letter, inspectional observation, or other government inquiry tied to bulk drug substance sourcing. Early legal intervention can protect the facility's rights, shape its response to FDA requests, avoid inadvertent admissions, preserve relevant defenses, and allow counsel to communicate with FDA on the facility's behalf. Delaying representation can significantly affect the outcome of a matter and expose the facility to unnecessary risk.

How Health Law Alliance Can Help

Health Law Alliance's compounding pharmacy attorneys advise 503A pharmacies and 503B outsourcing facilities on bulk drug substance sourcing, including nomination strategy and shortage-list monitoring for the GLP-1 class. If your facility relies on a substance whose 503B Bulks List status is uncertain, contact us for a free, confidential consultation.