FDA Proposes Removing Semaglutide, Tirzepatide, and Liraglutide from the 503B Outsourcing Bulks List

FDA Proposes Regulatory Changes to the 503B Outsourcing Bulks List

The U.S. Food and Drug Administration has issued a formal proposal to remove three GLP-1 receptor agonist drugs — semaglutide, tirzepatide, and liraglutide — from the list of bulk substances that licensed 503B outsourcing facilities are permitted to use in compounding operations. The agency's stated rationale centers on its assessment that no sufficient clinical need exists for these particular substances to be compounded from bulk starting materials by outsourcing facilities at this time.

### What Is the 503B Bulks List?

Under Section 503B of the Federal Food, Drug, and Cosmetic Act, registered outsourcing facilities may compound drug preparations from bulk substances, provided those substances appear on an FDA-nominated and evaluated list. Placement on this list is not automatic — the FDA conducts reviews that weigh factors such as whether an FDA-approved finished drug product is already available, the medical rationale for compounding, and whether compounding from bulk substances would present additional risk considerations.

When the agency determines that approved alternatives adequately address the landscape, it may propose to exclude a substance or decline to add it. That is precisely the regulatory mechanism being invoked here.

### The Proposal and Its Scope

According to the FDA's press announcement, the agency is moving to formally exclude semaglutide, tirzepatide, and liraglutide from 503B bulk compounding eligibility. All three compounds have FDA-approved finished drug counterparts — including commercially developed formulations — which the agency cited as part of its evaluation framework. The FDA noted that, given the existence of these approved products, the agency did not identify a basis for concluding that bulk compounding of these substances by outsourcing facilities is warranted under the current statutory criteria.

This proposal follows a period during which drug shortages had previously created a regulatory opening for compounded versions of GLP-1 class drugs to enter the market through both 503A pharmacies and 503B outsourcing facilities. As shortage designations have been updated, the FDA has moved to reassess the ongoing regulatory status of these substances in the compounding framework.

### Implications for the Research and Regulatory Landscape

From a research standpoint, semaglutide, tirzepatide, and liraglutide are each investigated in the context of metabolic pathway research, GLP-1 receptor signaling studies, and related preclinical models. The regulatory action described here pertains specifically to the compounding and commercial distribution framework under 503B — it is a regulatory and institutional development, not a scientific one.

Researchers working with these compounds in in vitro systems or animal models operate under entirely separate frameworks governed by institutional review, DEA scheduling status (where applicable), and standard research-use-only sourcing protocols. The FDA proposal does not alter the scientific literature surrounding these molecules, nor does it affect their status as subjects of ongoing basic and translational research.

Stakeholders in the outsourcing and compounding industry will have an opportunity to submit comments during the public comment period that accompanies the proposed rule. The FDA's formal process includes review of those submissions before any final determination is made.

### Research Context

Semaglutide is investigated in research models examining GLP-1 receptor activation and downstream signaling cascades. Tirzepatide, a dual GIP/GLP-1 receptor agonist, is studied in preclinical contexts related to receptor pharmacology and metabolic biology research. Liraglutide has been the subject of research examining pancreatic beta-cell biology and neuroendocrine signaling pathways in animal models. Each of these areas of inquiry remains active regardless of the regulatory developments described above.

The FDA's proposal represents a significant institutional action within the compounding regulatory space, and the research community will be watching the public comment process closely as the agency moves toward a final rule.

*For research use only. Not for human or animal consumption.*