FDA proposes permanently excluding semaglutide, tirzepatide and liraglutide from 503B bulks list: compounding of GLP-1 peptides faces definitive end

What has the FDA proposed?

The US Food and Drug Administration (FDA) has moved to permanently exclude semaglutide, tirzepatide and liraglutide from the 503B Bulks List — the register of bulk drug substances that outsourcing facilities may use to compound drugs under Section 503B of the Federal Food, Drug, and Cosmetic Act.

If finalised, the proposal would make it unlawful for 503B outsourcing facilities to compound products containing these three GLP-1 receptor agonists, closing a regulatory pathway that had been used to supply compounded versions of Wegovy, Ozempic, Mounjaro and Saxenda during periods of branded-drug shortage.

Context: from shortage to permanent exclusion

Compounded GLP-1 products proliferated during the semaglutide and tirzepatide shortages of 2023–2024. Outsourcing facilities operating under Section 503B were permitted to compound these drugs using bulk active pharmaceutical ingredients (APIs) while the drugs remained on the FDA's shortage list.

In late 2024, the FDA formally resolved the semaglutide shortage, triggering a wind-down period for compounding. The new proposal goes further: rather than simply waiting for shortage status to lapse, the FDA is proposing to remove these substances from the 503B Bulks List altogether, making the exclusion permanent regardless of future shortage designations.

Why is the FDA taking this step?

The FDA's rationale centres on several factors:

Patient safety: Compounded GLP-1 products have been linked to adverse events, including reports of incorrect dosing, contamination and the use of non-pharmaceutical-grade salts (such as semaglutide sodium rather than the approved base form).
Market availability: With branded supply now sufficient to meet demand, the public health justification for compounded alternatives has diminished.
Regulatory clarity: The proposal provides a definitive position rather than relying on the temporary status of shortage lists, which can change.

The agency has also raised concerns about improper supply of GLP-1 medicines, including compounding operations that may not have met current good manufacturing practice (cGMP) standards.

What does this mean for peptide researchers?

For the research-peptide community, the proposal has several implications:

Reduced availability of compounded GLP-1 APIs: Outsourcing facilities that previously sold compounded semaglutide and tirzepatide to clinics and research institutions may cease production, tightening the supply of these peptides for research purposes.
Increased scrutiny of research-grade suppliers: With the compounding pathway closing, researchers may increasingly turn to dedicated research-peptide vendors. The FDA's heightened attention to GLP-1 products may extend to suppliers marketing these substances for non-clinical use.
UK and EU ripple effects: While the FDA's 503B framework is US-specific, the regulatory signal reinforces a global trend of tightening oversight on GLP-1 compounds. The MHRA has separately reiterated that GLP-1 medicines are prescription-only in the UK, and improper supply — including via online channels — remains an enforcement priority.

UK regulatory position

In the UK, semaglutide (Wegovy, Ozempic), tirzepatide (Mounjaro) and liraglutide (Saxenda) are licensed prescription-only medicines (POMs). They are not approved for over-the-counter supply, and compounding these substances for human use without a licence would contravene the Human Medicines Regulations 2012.

For research purposes, these peptides may be sold by research-chemical suppliers provided they are clearly labelled and marketed as 'not for human consumption' and 'for research use only'. The FDA's proposal does not directly affect UK research-supply channels, but it underscores the regulatory direction of travel.

What happens next?

The FDA's proposal will go through a public comment period before a final rule is issued. Outsourcing facilities and interested parties may submit comments, but the agency's direction appears clear. Researchers who rely on compounded GLP-1 products should anticipate reduced availability and plan accordingly.

This article is for research and educational purposes only and does not constitute medical or legal advice.

This article is AI-researched and editorially reviewed. It is provided for research and educational purposes only and is not medical advice. Research peptides are not licensed for human consumption in the UK.