Eight Days Left: FDA's 17 Revised Draft Peptide Guidances and What the Withdrawn 2021 Framework Means for Generic Developers

Key takeaways

• The FDA published 17 revised draft product-specific guidances (PSGs) for generic peptide products on 28 July 2026; the public comment window closes 28 September 2026.
• The PSGs cover calcitonin salmon, dasiglucagon, glucagon, liraglutide, pegcetacoplan, semaglutide, teriparatide, tirzepatide, and vosoritide across 16 brand-name reference products, plus one additional formulation variant.
• Five technical areas were updated: ANDA submission pathways for recombinant, synthetic, and semi-synthetic peptides; innate immune response testing; impurity thresholds; higher-order structure assessment; and biological activity assessment.
• The FDA simultaneously withdrew its May 2021 guidance on ANDAs for highly purified synthetic peptide drug products referencing biologics-origin drugs, citing scientific obsolescence — a replacement is expected later in 2026 but no text has been published.
• Sponsors and CDMOs whose chemistry, manufacturing and controls (CMC) packages were designed around the 2021 framework now face a narrow window to identify gaps before the revised PSGs are finalised.

What the FDA published and why it matters

The FDA announced on 28 July 2026 that it had published 17 revised draft PSGs for peptide products — described by the agency as "a significant advancement in the agency's scientific and regulatory approach to generic peptide drug assessment." The Federal Register notice carrying the accompanying withdrawal notice was published the following day, and the public comment period is set to close on 28 September 2026.

Product-specific guidances are not binding regulations. They are recommendations that tell generic-drug developers what evidence the FDA expects in an abbreviated new drug application (ANDA), addressing how to demonstrate bioequivalence to the brand-name product and what analytical and quality data the agency expects to review. A sponsor may propose an alternative approach to bioequivalence study design, though departures from the published recommendations generally invite closer regulatory scrutiny than following them directly.

The comment deadline falls in eight days. For UK-based laboratories and CDMOs supplying API or reference materials into programmes targeting the US generic market, this window to formally influence the final standards is narrow and should not be overlooked.

The 17 reference products covered

The revised PSGs address the following reference drugs:

• Calcitonin salmon (Calcimar; Miacalcin) — for osteoporosis
• Dasiglucagon hydrochloride (Zegalogue) — for hypoglycaemia
• Glucagon (Baqsimi; Glucagon; Gvoke) — for hypoglycaemia
• Liraglutide (Victoza; Saxenda) — for type 2 diabetes and obesity
• Pegcetacoplan (Syfovre; Empaveli) — for macular degeneration and paroxysmal nocturnal haemoglobinuria
• Semaglutide (Ozempic; Wegovy) — for type 2 diabetes and obesity
• Teriparatide (Forteo; Teriparatide) — for osteoporosis
• Tirzepatide (Mounjaro; Zepbound) — for type 2 diabetes and obesity
• Vosoritide (Voxzogo) — for achondroplasia

The reference drugs span conditions including obesity, type 2 diabetes, osteoporosis, and macular degeneration, illustrating that the FDA's updated framework is a cross-portfolio harmonisation of peptide characterisation standards rather than an intervention targeted solely at the GLP-1 class.

Five technical areas updated

The revised PSGs provide updated recommendations across five domains:

1. ANDA submission pathways — updated expectations for recombinantly, synthetically, or semi-synthetically produced peptides seeking abbreviated approval.
2. Innate immune response testing — new or revised testing expectations to characterise the potential for non-specific immune activation distinct from adaptive immunogenicity.
3. Impurity thresholds — revised limits and testing methodologies for peptide-related impurities, which are particularly consequential given that impurities in peptide generics carry both quality and immunogenicity implications that differ from small-molecule generics.
4. Higher-order structure assessment — updated approaches for characterising three-dimensional conformation, which affects bioequivalence determinations for larger or more structurally complex peptides.
5. Biological activity assessment — revised expectations for demonstrating functional equivalence between generic and reference products.

For generic developers working on semaglutide, tirzepatide, liraglutide, and other high-value peptides, this represents the most significant shift in the ANDA pathway for peptides in years, according to regulatory counsel tracking the docket.

The withdrawn 2021 guidance: the practical problem

The element of this update most likely to disrupt active development programmes is the simultaneous withdrawal of the May 2021 guidance. The FDA withdrew the guidance titled ANDAs for Certain Highly Purified Synthetic Peptide Drug Products That Refer to Listed Drugs of rDNA Origin on 28 July 2026, stating that it "no longer reflects FDA's current scientific thinking". The agency has indicated it plans to issue a replacement later in 2026, per the CDER 2026 Guidance Agenda, but no replacement text or firm publication date has been confirmed.

This creates an interim gap. Sponsors who structured their CMC packages and sameness arguments around the 2021 framework now face a period in which the document they relied upon no longer carries regulatory authority, while its replacement remains unpublished. The 17 revised draft PSGs partly fill that space for the specific reference products they cover, but the broader synthetic-peptide population — any peptide not among the 17 covered products — is currently navigating without the overarching guidance framework that defined the baseline from 2021 onwards.

Inclusion of semaglutide and tirzepatide in the updated guidances also signals that the FDA is actively laying the analytical groundwork for generic competition as patents and exclusivity periods approach their end. Updated thresholds for impurities and revised expectations for structural and functional characterisation can require redevelopment for programmes already in flight, particularly for organisations that had advanced CMC work prior to 28 July.

Compounding context: a distinct but related signal

The generic ANDA pathway is separate from the compounding pharmacy framework, but the two interact in practice. As of early 2025, the FDA had received more than 455 adverse event reports linked to compounded semaglutide and more than 320 linked to compounded tirzepatide, many involving dosing errors requiring hospitalisation. That adverse event record has reinforced the agency's drive to establish rigorous analytical standards for any non-originator peptide product entering the market, whether through the ANDA or compounding route.

The semaglutide and tirzepatide shortages that justified compounding pharmacy access to these molecules were resolved in February and December 2024–25 respectively, and phased enforcement grace periods have now expired. The revised PSGs therefore arrive at a moment when the regulatory boundary between approved generics and compounded alternatives is under renewed scrutiny at the FDA.

What research-procurement teams should note

For UK laboratories procuring peptide reference standards, impurity markers, or API from suppliers whose clients include US generic developers, the near-term implications are practical:

• Comment window closes 28 September 2026. Organisations with a substantive view on the proposed impurity thresholds, immune-response testing requirements, or higher-order structure assessment methodologies have one week to engage with the docket electronically via regulations.gov or in writing to the FDA's Dockets Management Staff.
• CMC package reviews are advisable now. Sponsors whose development plans were calibrated to the 2021 guidance should audit the gap between their existing CMC documentation and the five revised areas before the draft PSGs are finalised.
• The replacement framework for the withdrawn 2021 guidance is pending. Until the FDA publishes revised general guidance for synthetic peptide ANDAs — expected before year-end 2026 per the CDER agenda — the regulatory environment for peptides not covered by one of the 17 PSGs is operating without a current general framework document.
• Supply chain positioning. For CDMOs and analytical laboratories, the updated impurity thresholds and structural characterisation expectations in the PSGs represent the clearest available signal of where the bar will sit for the next wave of generic peptide approvals, particularly for GLP-1 class molecules where commercial interest is highest.

The FDA's formal announcement is available at fda.gov, and the Federal Register notice was published 29 July 2026 (Vol. 91, No. 144). Comments can be submitted to the FDA docket referenced in that notice before 28 September 2026.