May 2026 in Peptides: TRIUMPH-1, the Maintenance Pivot, and the First HDV Drug

May 2026 was a conference month, and three meetings set the agenda. ECO 2026 in Istanbul (May 12–15) turned the obesity conversation from how much weight a drug removes to whether patients can keep it off, with SURMOUNT-MAINTAIN in The Lancet and ATTAIN-MAINTAIN in Nature Medicine landing the same week as a new EASO first-line framework. On May 21, Lilly's TRIUMPH-1 topline gave retatrutide a 28.3% mean weight loss at 80 weeks, the highest Phase 3 obesity number on record, alongside a dysesthesia signal at the top dose. EASL 2026 in Barcelona (May 27–30) confirmed MASH as a multi-mechanism field, with survodutide in NEJM, pemvidutide, Aligos, Arrowhead, and Madrigal all dropping data, while a separate thread opened the HBV/HDV functional-cure race, anchored by Gilead's May 22 approval of Hepcludex (bulevirtide), the first US treatment for hepatitis delta and a 47-amino-acid lipopeptide. ASCO 2026 in Chicago (May 29 onward) moved peptide oncology from abstract to podium across Bicycle, Avacta, Corbus, BriaCell, Telix, Immutep, and Mayo. Underneath it all, Novo's oral semaglutide pulled decisively ahead of Lilly's Foundayo in the launch race, Mounjaro overtook Keytruda as the world's top-selling drug, and the FDA kept tightening the compounding channel.

The oral GLP-1 launch race tilted hard toward Novo Nordisk in May. The company retired the Rybelsus brand and relaunched the same molecule as the Ozempic Pill in 70,000-plus US pharmacies starting May 4, with GoodRx self-pay tiers at $149, $199, and $299 per month by strength. Its obesity counterpart, the Wegovy pill, reached roughly 113,000 weekly US prescriptions by early May, posted $354 million in Q1 sales (about twice consensus), and surpassed one million US users 16 weeks after launch. Wegovy accounted for 65% of new US GLP-1 prescriptions, a position CEO Mike Doustdar framed as a turnaround.

Lilly's Foundayo (orforglipron) climbed but stayed far behind: IQVIA readings ran 5,612 prescriptions in launch week three, then 7,335, 10,248, and roughly 17,000 by the week ending mid-May. A Foundayo liver-failure FAERS report surfaced on May 4 and knocked the stock before Lilly released updated safety data from its 11,000-patient program showing no drug-induced liver injury signal, which RBC called baseline noise rather than a mechanism.

ECO 2026 in Istanbul reframed obesity treatment around durability. Lilly published two maintenance trials on May 12: SURMOUNT-MAINTAIN in The Lancet showed patients held on the maximum tolerated tirzepatide dose were seven times more likely to maintain their weight loss than those switched to placebo, and a 5 mg step-down held a four-fold edge; ATTAIN-MAINTAIN in Nature Medicine showed adults switching off injectable semaglutide or tirzepatide to once-daily oral orforglipron kept most of their loss, regaining about 1 kg (semaglutide switch) and 5 kg (tirzepatide switch) over 52 weeks. A new EASO framework in Nature Medicine, presented May 14, put semaglutide and tirzepatide first-line with a complication-specific algorithm.

The pipeline filled in around them. Viking's oral VK2735 delivered 12.2% mean weight loss (26.6 lbs) at 13 weeks; CagriSema's REDEFINE 1 body-composition substudy showed 35.7% fat-mass loss and moved 50.7% of treated patients below a BMI of 30; higher-dose Wegovy 7.2 mg drove 28% loss in early responders; Innovent's mazdutide GLORY-2 posted 18.55%; and AstraZeneca's oral eleglipron met its Phase 2b endpoints. A Prime Therapeutics claims analysis supplied the counterweight: just 8.1% of patients stayed on anti-obesity medication for three years.

On May 21, Eli Lilly released TRIUMPH-1 topline data, the registrational Phase 3 readout for the triple GLP-1/GIP/glucagon agonist retatrutide. In 2,339 adults with obesity or overweight and at least one weight-related comorbidity without diabetes, retatrutide produced 28.3% mean weight loss at 12 mg, 25.9% at 9 mg, and 19.0% at 4 mg over 80 weeks, against 2.2% on placebo. Among 12 mg patients, 45.3% reached at least 30% weight loss, a threshold that overlaps bariatric-surgery outcomes, and a 104-week extension in the BMI ≥35 subgroup pushed mean loss to 30.3%.

The safety profile drew the closest reading. Discontinuation ran 4.1%, 6.9%, and 11.3% across the 4, 9, and 12 mg arms versus 4.9% on placebo, and analysts flagged a dose-dependent dysesthesia signal (about 12.5% at 12 mg) tied to glucagon-receptor activation, alongside transient ALT elevations that normalized by week 24. William Blair read a high-BMI confinement into the discontinuation curve; Leerink and RBC called it a clean win. Full data lands at ADA 2026 in June.

EASL 2026 in Barcelona settled any question about whether MASH has one winning mechanism. Boehringer and Zealand published full 48-week survodutide Phase 2 data in NEJM, with MASH improvement and no fibrosis worsening in 47–62% of patients versus 14% on placebo. Altimmune's pemvidutide IMPACT trial showed qFibrosis regression at 24 weeks and, at 48 weeks, a 1.8 mg dose cutting triglycerides 23.7% and weight 7.5% at roughly 1% discontinuation. Aligos' ALG-055009, a THR-β agonist, hit 46.2% placebo-adjusted liver-fat reduction at 12 weeks; Arrowhead's RNAi candidate ARO-INHBE cut liver fat 44%; and Madrigal added eight Rezdiffra posters spanning cardiovascular and portal-hypertension markers.

The meeting's other thread was viral. Gilead won FDA accelerated approval for Hepcludex (bulevirtide-gmod) on May 22, the first and only US treatment for chronic hepatitis delta and a 47-amino-acid lipopeptide that blocks the NTCP entry receptor shared by HBV and HDV. Around it, the functional-cure field showed its range: Assembly's oral ABI-6250 entry inhibitor, Precision's PBGENE-HBV gene editor reporting the first evidence of cccDNA elimination in patient biopsies, TUNE-401's epigenetic silencer, and Brii's BRII-179 therapeutic vaccine.

ASCO 2026 abstracts dropped May 21 and the meeting opened May 29 in Chicago, loading the calendar with peptide and conjugate oncology. Bicycle Therapeutics' Duravelo-2 showed a 65% objective response rate for the bicyclic peptide-drug conjugate zelenectide pevedotin plus pembrolizumab in first-line urothelial cancer. Corbus' CRB-701 Nectin-4 ADC posted 42.9% ORR in second-line oropharyngeal and 34.4% in cervical cancer. Avacta's FAP-activated AVA6000 held salivary-gland responses; Sapience's lucicebtide projected a 28.4-month median PFS in glioblastoma; BriaCell's Bria-IMT reported 16.6-month median overall survival in heavily pretreated breast cancer; Telix's ProstACT PSMA radioligand met its Phase 3 Part 1 safety objectives; and Immutep's eftilagimod alfa showed a 7.7-month survival gain in immune responders across 592 patients.

The deal side moved too. Regeneron and Parabilis Medicines signed a $2.325 billion antibody-helicon-conjugate collaboration, and Parabilis filed for an IPO on the strength of its helical peptide zolucatetide, which posted a 74% response rate in desmoid tumors.

The compounding channel kept narrowing. The FDA's April 30 proposal to strike semaglutide, tirzepatide, and liraglutide from the 503B outsourcing-facility bulks list ran through its comment window, which closes June 29, while BSR Intelligence reported compounded semaglutide shipments down 90% year over year and counterfeit purity ranging from 5% to 75% with lead levels ten times the safety limit. The FDA sent a warning letter to Chinese supplier Harbin Jixianglong on May 20 over semaglutide API sourced from a non-green-list facility, and added an AI-informed inspection pilot on May 15 that will apply machine learning to facility reviews, peptide manufacturing included.

State enforcement diverged, with California logging more than 30 actions since 2023 against a more permissive Texas posture for licensed 503A operations. Telehealth pricing kept compressing, with Ozari Health anchoring compounded semaglutide at $86 a month. The fixed regulatory point remains the July 23–24 PCAC meeting on whether seven research peptides (BPC-157, KPV, TB-500, MOTs-C, Emideltide, Semax, and Epitalon) should join the 503A bulks list.

The non-GLP-1 field had a full month. Nature published the TransCODE consortium's addition of 1,785 microproteins to the human proteome on May 6, expanding it by about 10% and formalizing a "peptideins" framework that widens the druggable map. In neuromuscular disease, Entrada's ENTR-601-44 posted a statistically significant 2.36% mean dystrophin increase in Duchenne muscular dystrophy, while PepGen abandoned its DMD program after a 0.59% dystrophin reading and pivoted to myotonic dystrophy, where Vertex's cyclic-peptide-oligonucleotide conjugate VX-670 also advances.

Radioligands and depots stacked up regulatory dates: Crinetics' oral acromegaly drug Palsonify booked $10.3 million in its first full quarter, Camurus' octreotide depot Oclaiz carries a June 10 PDUFA, and ITM's Lu-edotreotide-177 has an August 28 PDUFA in neuroendocrine tumors. Amylyx opened an expanded-access program for the GLP-1 antagonist avexitide in post-bariatric hypoglycemia, Entera submitted a Phase 3 plan for its oral PTH tablet EB613, and the cosmetic wave kept building, with Neurogan's 2% GHK-Cu body care and a clutch of copper-peptide and hair-peptide launches.

May reordered the pharmaceutical leaderboard. Mounjaro became the world's top-selling drug at $8.66 billion in Lilly's Q1 versus Keytruda's $7.9 billion, ending the checkpoint inhibitor's two-year reign. Novo reported Q1 on May 6 with the Wegovy pill beat offset by tightened full-year guidance; Hims & Hers printed $608 million in Q1 revenue on May 11 but closed that week down 13% as the compounded-semaglutide wind-down compressed margins and analysts split on the GLP-1 pivot.

Manufacturers spent against the demand curve. Lilly committed an additional $4.5 billion to its Lebanon, Indiana sites, including a first dedicated genetic-medicine facility tied to Foundayo and retatrutide; CordenPharma confirmed a $500 million Boulder solid-phase peptide expansion; and PolyPeptide widened its credit facility to €200 million. On the access side, Health Canada approved a second generic semaglutide (Apotex) on May 1, and a Lancet analysis put generic semaglutide production cost at $28–140 per person-year, enough to reach 84% of the global obesity burden by year-end.

June front-loads its biggest event. ADA 2026 opens June 5–8 in New Orleans, where Lilly presents full TRIUMPH-1 data plus retatrutide's first diabetes Phase 3, TRANSCEND-T2D-1 (A1C down up to 2.0%, 16.8% weight loss at 40 weeks), and oral Foundayo's head-to-head win over oral semaglutide. Innovent's mazdutide brings GLORY-2 and the DREAMS-3 head-to-head versus semaglutide; AstraZeneca's eleglipron carries full Phase 2b data; and Lilly's GLP-1/GIP/glucagon/amylin/calcitonin quintuple agonist takes a plenary slot. ASCO runs through June 2 with the Bicycle, Mayo TPIV200, and Telix ProstACT podium readouts.

The regulatory calendar tightens around two dates: Camurus' octreotide depot Oclaiz has a June 10 PDUFA, and the FDA's 503B GLP-1 exclusion comment window closes June 29, with Lantheus' PNT2003 Lutathera radioequivalent moving into its approval window the same month. Roche's petrelintide-plus-enicepatide Phase 2 combination is set to open mid-year, and the July 23–24 PCAC meeting on the seven research peptides remains the field's next regulatory fixed point. May built the positions; June tests how much of the data holds up at full readout.