Tirzepatide is Eli Lilly's GLP-1/GIP dual agonist, sold as Mounjaro for type-2 diabetes and Zepbound for obesity. The Phase 3 SURMOUNT and SURPASS programs established it as the most potent incretin therapy approved.
SURMOUNT-5, the head-to-head against semaglutide, read out in April 2026 with 21.6% mean weight loss at 72 weeks versus 15.4% for semaglutide; 36.2% of tirzepatide patients hit ≥25% weight loss versus 19.4% on semaglutide. The drug also has FDA approval for moderate-to-severe obstructive sleep apnea via the SURMOUNT-OSA program, and Truveta EHR data presented at OMA 2026 reproduced the head-to-head signal in routine 12-month care.
Like semaglutide, tirzepatide sits on the FDA's April 30, 2026 proposal to exclude branded actives from the 503B bulks list. Stories here track new readouts, the head-to-head economics, and the long compounding fight.
An ECO 2026 analysis covered May 18 by ScienceDaily examined 89,718 patients starting GLP-1 therapy — 75.6% semaglutide, 17.5% tirzepatide, 6.9% liraglutide — and stratified BMI change at year one. In the first year, 27% reduced BMI by less than 5%, 22.4% by 5-10%, 14.1% by 10-15%, and 15.8% by ≥15%, while 20.8% actually gained weight. Greater weight loss correlated with larger reductions in obesity-related risk endpoints; patients who gained weight after starting treatment faced worse health outcomes than untreated comparators in several measures.
The EASO 2026 Nature Medicine framework published May 14, presented at ECO 2026 — formally privileging semaglutide and tirzepatide as first-line therapy across most obesity complications with differentiated complication-specific recommendations — has generated initial reception coverage. The Endocrine Society and American Diabetes Association haven't yet issued formal endorsement or counter-response statements as of May 16, though informal commentary from US endocrinologists has been broadly favorable. The framework's main US-specific gap is its silence on cost and insurance access — the algorithm assumes prescribers can choose between semaglutide and tirzepatide based on clinical indication, but US patients without diabetes face the Medicare Part D weight-loss-only exclusion. The Medicare GLP-1 Bridge launching July 1, 2026 partly addresses that gap; broader integration awaits CMS rulemaking. ADA 2026 Scientific Sessions in New Orleans June 5-8 will be the next inflection point for guideline alignment between US and EASO positions.
The Lancet formalized SURMOUNT-MAINTAIN on May 14, 2026, the same day the trial was presented at ECO 2026 in Istanbul. The Phase 3b 112-week study from Dr. Deborah Horn and colleagues at UTHealth Houston re-randomized patients who had reached maximum tolerated dose tirzepatide to continue MTD (15 mg or 10 mg), step down to 5 mg, or switch to placebo. Patients continuing MTD were 7x more likely to maintain their weight loss than those switching to placebo; the 5 mg step-down arm was 4x more likely than placebo. At week 112, MTD continuers preserved all of their initial weight loss; 5 mg-step-down patients lost only 5.6 kg of their initial gains on average. The 'seven times more likely' framing — picked up by EurekAlert and the daily science press — is the cleanest patient-facing summary of maintenance economics published to date.
The European Association for the Study of Obesity published an updated pharmacological framework in Nature Medicine, presented at ECO 2026 in Istanbul on Thursday May 14. Semaglutide and tirzepatide are recommended as first-line treatment for obesity across most complications. Tirzepatide is preferred for obstructive sleep apnea and MASH; semaglutide is preferred for knee osteoarthritis and established cardiovascular disease — and is the only agent with current evidence supporting MASH-fibrosis improvement. The framework integrated evidence through November 21, 2025 from 62 randomized controlled trials. The algorithm uses obesity-related complication presence as the primary treatment-selection factor and provides the first major obesity-society guideline to formally privilege incretin-based therapy across the indication mix.
Eli Lilly published SURMOUNT-MAINTAIN in The Lancet and ATTAIN-MAINTAIN in Nature Medicine on May 12, with concurrent presentation at ECO 2026 in Istanbul. SURMOUNT-MAINTAIN tested lower-dose Zepbound (tirzepatide 5 mg) vs maximum tolerated dose: at week 112, MTD preserved all weight loss while the 5 mg arm lost only 5.6 kg additional. ATTAIN-MAINTAIN tested Foundayo (orforglipron) as a switch from injectable GLP-1s in SURMOUNT-5 participants: orforglipron preserved 79.3% of injectable-phase weight loss vs 37.6% on placebo at week 52; Wegovy MTD switchers regained only 0.9 kg, Zepbound MTD switchers regained 5.0 kg. The dual readout reframes the maintenance-versus-discontinuation conversation: dose-tapering and oral-switching strategies now have Phase 3 evidence behind them, validating the long-term-treatment chronic-disease framing.
Bloomberg reported May 6 that Eli Lilly's Mounjaro displaced Merck's Keytruda as the world's best-selling pharmaceutical in Q1 2026 — $8.66B Mounjaro Q1 sales vs Keytruda's $7.9B Q1 sales. The Mounjaro+Zepbound combined tirzepatide platform generated $36.5B in 2025, outpacing Keytruda's $31.6B. Keytruda had held the #1 ranking since Q1 2023, when it displaced AbbVie's Humira. The shift is the first time a peptide therapeutic has taken the top spot since the historical run of insulin biosimilars. The narrative also frames Lilly's $4.5B Lebanon Indiana manufacturing recommitment and the broader $21B Indiana capital plan as the supply-chain answer to demand at that scale.
Barclays analyst Emily Field raised her price target on Eli Lilly to $1,400 from $1,350 May 5 and reiterated an Overweight rating, citing tirzepatide momentum continuing to outpace the GLP-1 class and easing concerns around the Foundayo launch trajectory. LLY stock had recovered roughly 11% off the May 4 Foundayo FAERS-driven dip to about $966 by mid-week. Barclays simultaneously trimmed its 2026 Foundayo revenue estimate to approximately $1B (vs. ~$1.4B consensus) on the early IQVIA gap to Wegovy pill, but the higher headline target reflects confidence that Mounjaro and Zepbound's volume growth more than absorbs Foundayo's slower start.
Eli Lilly stock has gained roughly 11% over the past week, recovering from the May 4 Foundayo hepatic-failure FAERS report-driven 3% premarket dip and consolidating gains from the April 30 Q1 beat. Per the May 6 analyst consensus across 19 covering firms, LLY now carries an average 12-month price target of $1,228 — implying 24.15% upside from current $966 — with a Buy consensus rating. The recovery framework: tirzepatide volume (+125% global Q1 growth) anchors the floor, retatrutide TRIUMPH program (seven Phase 3 readouts due in 2026) anchors the upside, the small-molecule manufacturing economics of Foundayo offset peptide CDMO bottlenecks, and Pfizer's MariTide/MET-097i and Novo's CagriSema higher-dose program don't read out until 2027.
Eli Lilly reported Q1 2026 worldwide revenue of $19.8 billion, up 56% year over year on 65% volume growth partially offset by a 13% price decline. Mounjaro hit $8.66 billion globally (+125%), Zepbound delivered $4.16 billion in U.S. sales (+80%), and reported Q1 EPS jumped 170% to $8.26. Lilly raised 2026 revenue guidance by $2 billion at each end to $82–85 billion and lifted non-GAAP EPS guidance to $35.50–$37.00. The release also recapped five positive Phase 3 readouts, six new Phase 3 starts, and the closings of the Orna, Centessa, Colonia, and Ajax acquisitions in the quarter.
The FDA announced a proposal on April 30 to exclude semaglutide, tirzepatide, and liraglutide from the 503B outsourcing-facility bulks list, finding no clinical need for large-scale compounding now that branded supply has stabilized. Commissioner Marty Makary said outsourcing facilities cannot lawfully compound from bulk substances when FDA-approved drugs are available unless a clear clinical need exists. Public comments are open through June 29, 2026. The proposal targets 503B outsourcing facilities only and does not directly affect 503A patient-specific compounding, but it forecloses the largest legal pathway for branded-active GLP-1 compounding.
Fractyl Health's REMAIN-1 study — the first blinded, randomized, sham-controlled trial of an endoscopic 'gut reset' procedure — was accepted for presentation at DDW 2026. In 45 adults who had lost ≥15% body weight on tirzepatide and then discontinued, 29 received Revita duodenal mucosal resurfacing and 16 had a sham procedure. At 6 months post-discontinuation, Revita-treated patients regained 4.5% vs 7.5% for sham (P=0.07) — a 40% lower weight regain. Patients with more tissue resurfaced maintained >80% of pre-discontinuation weight loss. Topline pivotal-cohort data expected Q4 2026.
The first definitive Phase 3B head-to-head trial of Lilly's tirzepatide versus Novo Nordisk's semaglutide in 750 patients with obesity over 72 weeks showed tirzepatide produced 21.6% mean weight loss vs semaglutide's 15.4%. 36.2% of tirzepatide patients achieved ≥25% weight loss vs 19.4% on semaglutide. Results published April 20 give Lilly a clear comparative data point in the GLP-1 market share battle.
A University of Colorado Anschutz-led secret shopper study presented at Obesity Medicine Association 2026 surveyed 75 weight-loss clinics and medspas across two US states. 69 of 74 still offered compounded semaglutide and 65 of 74 offered compounded tirzepatide despite FDA resolving the name-brand shortages. Four source facilities had received FDA warnings or state licensing discipline since 2023 — three related to sterile compounding. Many clinics report using 'additive' formulations to skirt compounding restrictions.
The FDA published updated guidance clarifying compounding requirements now that semaglutide and tirzepatide shortages have been resolved. The statement reaffirmed enforcement deadlines for 503A and 503B pharmacies while acknowledging ongoing legal challenges from the Outsourcing Facilities Association.
A poster at the Obesity Medical Association annual conference (April 10-12, San Diego) showed tirzepatide achieved greater body weight reduction than semaglutide at 12 months in a real-world Truveta EHR analysis of adults with obesity without diabetes, consistent with SURMOUNT-5 clinical trial results.
A Mass General Brigham study of over 90,000 HFpEF patients published in JAMA found semaglutide reduced heart failure hospitalization or all-cause mortality by 42%, while tirzepatide achieved a 58% risk reduction compared with sitagliptin. Both drugs showed acceptable safety profiles with benefits appearing early in treatment.
A study in Scientific Reports found that early intervention with tirzepatide or semaglutide significantly reduced atherosclerotic plaque formation in ApoE-knockout mice, suggesting GLP-1 drugs may have preventive cardiovascular benefits beyond their metabolic effects when initiated before disease progression.
A federal grand jury indicted Utah osteopathic physician Justin Bradley Watkins for obtaining non-FDA-approved peptides including tirzepatide, semaglutide, BPC-157, and retatrutide from a Chinese supplier, affixing fake labels, and selling them to over 200 patients without disclosing their unapproved status.