FDA's 503B GLP-1 exclusion proposal, in plain English

On April 30, the FDA proposed adding semaglutide, tirzepatide, and liraglutide to the 503B “Do Not Compound” bulk drug substances list. The comment period closes June 29. If finalized, the rule would block one of the two compounding pathways that has kept lower-cost GLP-1 receptor agonists flowing to patients during the past two years of shortage.

This letter is what we wish someone had handed us the first time we read the press release.

503B vs 503A — the part most coverage skips

Drug compounding in the United States runs on two tracks.

503A pharmacies are traditional compounding pharmacies. They compound on a patient-by-patient basis from a prescription. They are state-licensed and inspected mainly by state boards of pharmacy, with FDA exercising authority where federal law applies.

503B outsourcing facilities were created by the Drug Quality and Security Act of 2013. They compound at larger volumes, can stock office-administered drugs, and operate under FDA cGMP-equivalent standards. They register directly with FDA and submit to FDA inspection.

The two tracks have separate bulks lists. A substance can be permitted under 503A while restricted under 503B, or vice versa. The April 30 proposal touches only the 503B side.

What “bulks list” means

Both 503A and 503B require that when a pharmacy compounds from a bulk active pharmaceutical ingredient (not from an FDA-approved finished drug), that ingredient must be one the agency has reviewed. The 503B framework specifies the categories that may appear on its list:

• Substances that appear on the list of bulks the FDA has determined are clinically necessary
• Substances that are on the FDA Drug Shortage List
• Substances whose addition to the list is under consideration

Until the April 30 proposal, semaglutide, tirzepatide, and liraglutide had been compounded by 503B facilities primarily under the shortage exception. The FDA declared semaglutide’s shortage resolved in early 2025 and tirzepatide’s resolved in late 2024. With shortages gone, the shortage exception no longer applies. The proposed rule would close the second possible door — being added to the consideration list — by formally placing the three substances on the exclusion list.

What the rule actually does

Three concrete effects, if finalized as written:

1. A 503B outsourcing facility cannot compound bulk semaglutide, tirzepatide, or liraglutide for any purpose. The exclusion is categorical, not conditional on shortage status.

2. Existing inventory cannot be sold off indefinitely. Outsourcing facilities will have a defined window — typically thirty to ninety days after a final rule — to use or destroy on-hand stock and active production.

3. 503A pharmacies are NOT covered by this proposal. Traditional compounding pharmacies operating under 503A still face the shortage-resolution problem (the FDA has used enforcement discretion to allow some 503A compounding during the GLP-1 shortage), but the April 30 proposal does not bind them.

A med-spa or clinic that has been sourcing compounded GLP-1s from a 503B outsourcing facility will need to find a different source if this rule finalizes. A patient relying on a 503A prescription should not assume the proposal does not affect them — the broader policy momentum is unfavorable to compounded GLP-1s on every track — but the April 30 proposal itself is specifically 503B.

Why FDA gave the reasons it did

The agency cited four general reasons in the proposal:

• The drugs are FDA-approved and commercially available for the indications most patients are receiving compounded versions for.
• The agency has documented adverse-event reports tied to compounded GLP-1 preparations, including dosing errors and incorrect salt forms.
• The agency has concerns about active ingredients that don’t meet U.S. Pharmacopeia (USP) manufacturing standards and non-pharmaceutical “research” salts (semaglutide acetate, semaglutide sodium) reaching consumer markets.
• Removing the substances from the 503B pathway, the FDA argues, does not deprive patients of access to the underlying drugs — the branded versions remain available.

The third reason is the one the comment period will mostly turn on. The branded products are available; what they are not, for many patients, is affordable. Whether that affordability gap is the FDA’s problem to solve is the policy question hidden inside this rule.

How the comment period works

This is the part most readers can actually participate in.

• The proposed rule has been published in the Federal Register.
• A 60-day public comment period is open. Comments close June 29.
• Comments are submitted at regulations.gov using the rule’s docket number, which the press release links.
• The FDA is legally required to review and respond to substantive comments before issuing a final rule. “Substantive” means a comment that raises a specific factual, scientific, or legal issue — not a form letter saying “I disagree.”
• A final rule typically follows the comment period by six to twelve months.

The most consequential comments are usually filed by physician groups, patient advocacy organizations, pharmacy boards, and the compounding industry itself. Individual patient comments matter less for legal weight but more for the public-record context that surrounds the rule.

What we will be watching

• The comment docket — for the structure of the opposing arguments.
• State pharmacy board responses, especially in states with active 503A compounding traditions.
• The pricing response from Novo Nordisk and Eli Lilly during the comment window. If branded prices remain at current levels, the affordability argument against the rule strengthens. If they fall, it weakens.
• Whether the FDA signals a parallel 503A action. Closing 503B without addressing 503A is a half-measure, and the agency historically does not stop at half-measures.

The shortest summary, for a busy reader: this is a real rule, on a fast clock, with one of the largest off-label medication markets in U.S. history hanging on it. If the comment period closes in June and a final rule issues this fall, the compounded-GLP-1 economy as it exists today does not survive that path through 503B.

We will publish the final rule the week it issues.

— The Editors