Research Updates

On April 30, 2026, the FDA issued a formal proposal that, if finalized, would permanently exclude semaglutide, tirzepatide, and liraglutide from the 503B Bulk Drug Substances List. The 503B pathway is the principal federal mechanism by which FDA-registered outsourcing facilities may compound from bulk active pharmaceutical ingredients at scale. With the underlying drug shortages resolved (semaglutide February 2025, tirzepatide December 2024), the FDA stated there is no clinical need for outsourcing facilities to compound these GLP-1 receptor agonists from bulk API when fully approved branded versions remain commercially available.

The proposal does not affect approved branded products (Ozempic, Wegovy, Rybelsus, Mounjaro, Zepbound, Saxenda, Victoza), and it does not directly govern Section 503A compounding pharmacies that prepare patient-specific prescriptions. It would, however, close the principal industrial-scale legal route by which much of the compounded GLP-1 supply has reached telehealth platforms and large clinic networks during 2024 and 2025.

The agency cited safety data as part of its rationale: more than 455 adverse-event reports linked to compounded semaglutide and more than 320 reports linked to compounded tirzepatide had been received as of early 2025, with many cases involving dosing errors from patients self-administering incorrect volumes from multidose vials. A 2024 analysis of compounded semaglutide samples from unregulated online sellers found that approximately 30 percent met basic quality standards, with assayed strengths ranging from roughly 0.4 percent to over 300 percent of labeled values.

The public comment period closes June 29, 2026. This proposal is procedurally separate from the April 15, 2026 removal of twelve healing peptides from Category 2 and from the upcoming July 23–24, 2026 Pharmacy Compounding Advisory Committee meeting, which concerns possible additions to the 503A Bulks List rather than the 503B exclusion at issue here. Several lawsuits filed by compounding pharmacies and telehealth companies challenging FDA's compounding-enforcement framework remain pending in federal court, and court rulings during the comment period could affect the proposal's trajectory.

A collaborative research effort led by Aivocode (a Sanford Burnham Prebys spin-off), IQAC-CSIC, and the University of California, Davis has published preclinical results for CAQK — a four-amino-acid peptide (Cys-Ala-Gln-Lys) — in models of acute traumatic brain injury. The findings, published in EMBO Molecular Medicine, demonstrate that intravenous CAQK selectively accumulates in injured brain tissue by binding to an extracellular matrix glycoprotein complex that is upregulated at injury sites.

In mouse models, CAQK administration reduced neuroinflammation, limited secondary cell death in damaged tissue, and improved functional recovery outcomes. The peptide also showed efficacy in a porcine TBI model, which more closely approximates human brain structure and injury dynamics. No obvious toxicity was observed in either species. The researchers attribute CAQK's selectivity to its affinity for chondroitin sulfate proteoglycans (CSPGs), which are deposited at sites of central nervous system injury but are largely absent from healthy brain tissue.

Aivocode has stated its intention to seek FDA authorisation for Phase I human clinical trials. As a short, simple peptide, CAQK has favourable drug development characteristics: it is easy to synthesise at scale, shows good tissue penetration, and is expected to be non-immunogenic. However, all efficacy data to date comes from animal models, and the transition from preclinical neuroprotection studies to human clinical benefit is historically challenging. No human pharmacokinetic or safety data exists yet.

If clinical development proceeds, CAQK would represent a novel approach to acute neuroprotection — an area with few effective interventions. Current standard of care for TBI is largely supportive, and no targeted pharmacological therapy has achieved FDA approval for acute brain injury. The targeted delivery mechanism (selectively homing to injured tissue via IV administration) is particularly noteworthy, as most neuroprotective candidates fail due to poor blood-brain barrier penetration or lack of specificity.

The FDA granted approval to Stealth BioTherapeutics' elamipretide (brand name Forzinity) for the treatment of Barth syndrome, a rare X-linked mitochondrial cardiomyopathy affecting primarily males. This marks a landmark regulatory milestone — the first FDA-approved therapy specifically for Barth syndrome and one of the very few approved mitochondria-targeting peptides in clinical use.

Elamipretide (SS-31) works by selectively targeting cardiolipin in the inner mitochondrial membrane, stabilising mitochondrial cristae architecture and improving electron transport chain efficiency. The approval was supported by the Phase III TAZPOWER extension trial, which demonstrated sustained improvements in skeletal muscle strength and exercise capacity over 36 weeks.

Post-marketing surveillance data for bremelanotide (Vyleesi), the FDA-approved subcutaneous peptide for hypoactive sexual desire disorder (HSDD) in premenopausal women, was compiled and analysed across multiple US healthcare systems. Real-world data broadly corroborated Phase III trial findings, with nausea remaining the most commonly reported adverse effect (occurring in roughly 40% of users) and transient blood pressure elevations noted in a subset of patients with pre-existing cardiovascular risk factors.

Prescribers reported that patient counselling on the nausea profile and on-demand dosing expectations significantly improved adherence and satisfaction outcomes. The data reinforced current label guidance recommending against use in patients with cardiovascular disease.

A pooled meta-analysis of 11 randomised and quasi-randomised trials (n = 1,847 patients) examined thymosin alpha-1 (Zadaxin) as an adjunct therapy in moderate-to-severe COVID-19. The analysis, published in a peer-reviewed infectious disease journal, found a statistically significant reduction in 28-day mortality (RR 0.71, 95% CI 0.58–0.87) and shorter ICU length of stay in the thymosin alpha-1 arms compared with standard-of-care controls.

The authors noted significant heterogeneity in dosing protocols (1.6 mg vs. 3.2 mg, twice weekly vs. daily) and cautioned that most trials were conducted in China, where Zadaxin is approved and commercially available, limiting generalisability. No serious adverse events attributable to the peptide were reported across the pooled cohort.

A Phase I dose-escalation safety trial for oral BPC-157 was registered and initiated, representing the first prospective controlled human trial for this widely researched peptide. The trial, sponsored by a Croatian academic consortium, enrolled healthy adult volunteers to evaluate pharmacokinetics, tolerability, and bioavailability of an orally administered BPC-157 formulation across three dose cohorts.

Prior to this trial, human use of BPC-157 had been exclusively anecdotal or extrapolated from an extensive animal literature. The initiation of a formal Phase I study is a significant step toward generating regulated safety data, though results are not expected until 2026 at the earliest.

Investigators published extended follow-up data from a two-year open-label continuation of an earlier MK-677 (ibutamoren) trial in older adults with GH deficiency. The analysis confirmed durable increases in IGF-1 and lean body mass but documented a clinically meaningful incidence of insulin resistance (fasting glucose elevation ≥10% from baseline in 23% of participants) and fluid retention requiring dose adjustment in 18%.

The data support prior short-term findings while reinforcing that metabolic monitoring — particularly fasting glucose and HbA1c — is essential during extended MK-677 use. The compound remains investigational and is not approved in any jurisdiction for anti-aging or body composition indications.

Researchers using transcriptomic profiling (RNA-seq) in human fibroblast and keratinocyte cell lines documented that GHK-Cu modulates expression of over 4,000 human genes — including upregulation of genes involved in antioxidant defence, DNA repair, and collagen synthesis, and downregulation of pro-inflammatory and oncogenic pathways.

While this in vitro work reinforces the pleiotropic signalling biology of GHK-Cu, the authors cautioned that gene expression changes in isolated cell lines do not directly translate to clinical outcomes. In vivo and clinical studies remain limited. The findings are consistent with earlier landmark work by Pickart et al. and extend the mechanistic rationale for topical and systemic GHK-Cu research.

Registry-based outcome analyses from Russian neurological centres where Semax (Met-Glu-His-Phe-Pro-Gly-Pro) is an approved pharmaceutical provided updated clinical data on its use in ischaemic stroke rehabilitation. Pooled registry data from 14 centres (n = 2,340 patients) reported that Semax adjunct therapy was associated with significantly improved neurological deficit scores (NIHSS) at 30 days and reduced rates of post-stroke cognitive impairment at 6 months compared with matched controls receiving standard rehabilitation alone.

This remains observational registry data rather than a randomised controlled trial, and Semax is not approved outside Russia and several former Soviet states. Independent replication in controlled Western trial settings is lacking.

Paradigm Biopharmaceuticals reported top-line Phase IIb results for intra-articular AOD-9604 (Pentosan Polysulfate Sodium — PPS) in knee osteoarthritis. The trial met its primary endpoint of pain reduction at 12 weeks (VAS score), with the 3-injection PPS group showing a statistically significant improvement over placebo (p = 0.031). Secondary endpoints of WOMAC function scores also trended favourably, though did not reach pre-specified significance thresholds.

Note: Paradigm's clinical programme primarily focuses on Pentosan Polysulfate Sodium rather than the AOD-9604 fragment peptide specifically; the two are distinct compounds that are sometimes conflated in online peptide communities. AOD-9604 itself (a lipolytic GH fragment) has no active regulated clinical programme as of 2024.