EASO First-Line: The New Obesity Treatment Algorithm by Complication, Explained

The European Association for the Study of Obesity published an updated pharmacological treatment framework in Nature Medicine on May 14, presented at the 33rd European Congress on Obesity in Istanbul. The document is the first major obesity-society guideline to formally state that GLP-1 receptor agonists belong at the top of the treatment algorithm for obesity and most of its complications. The 2026 update integrated evidence from 62 randomized controlled trials through November 21, 2025 — including the SURMOUNT-OSA, ESSENCE, SELECT, and TRIUMPH-4 readouts that have landed in the last 12-18 months.

The framework is a living document; the 2025 baseline version was already in print, and the 2026 update reorganized the algorithm around obesity complications rather than around drug class. That's the part of this guideline that actually matters for patients. Five years ago, the question a primary-care prescriber asked was 'is this patient a candidate for GLP-1 therapy at all?' Today the question is 'which complications does this patient have, and which GLP-1 is best for them?'

The framework splits obesity-related complications into two conceptual buckets that drive treatment selection: 'fat mass disease' (mechanical complications driven by adipose tissue load — osteoarthritis, sleep apnea, certain cancer risks) and 'sick fat disease' (immunological and metabolic complications driven by adipocyte dysfunction — type 2 diabetes, MASH, cardiovascular disease). For most patients these aren't mutually exclusive; a 55-year-old with knee osteoarthritis, sleep apnea, and pre-diabetes has all three categories at once. The algorithm tells you which complication should anchor the drug choice.

The top of the tree is consistent across complications: start with semaglutide 2.4 mg (Wegovy) or tirzepatide (Zepbound) as first-line therapy. Within that, the differentiated recommendations:

Tirzepatide preferred: obstructive sleep apnea, metabolic dysfunction-associated steatohepatitis (MASH).

Semaglutide preferred: knee osteoarthritis, established cardiovascular disease, MASH-associated fibrosis improvement.

Either acceptable, no clear preference: type 2 diabetes, dyslipidemia, hypertension, the baseline obesity indication itself.

Not recommended as first-line: older agents (orlistat, naltrexone-bupropion, phentermine-topiramate). Each retains a role for patients who can't tolerate or access GLP-1s, but the algorithm pushes them down to second- or third-line.

The SURMOUNT-OSA Phase 3 trial reported in 2024 that tirzepatide reduced apnea-hypopnea index (AHI) by 25-29 events per hour vs 5 events per hour on placebo, across both CPAP-using and CPAP-naive cohorts. The effect is well beyond what would be expected from weight loss alone; tirzepatide appears to have an OSA effect that has direct mechanistic pathways through upper-airway adipose tissue reduction and possibly central respiratory drive modulation. FDA approval for OSA followed in December 2024. The framework cites SURMOUNT-OSA as the strongest single piece of evidence behind a complication-specific first-line recommendation.

For MASH (formerly NASH), the case is more recent. Lilly's tirzepatide Phase 2 SYNERGY-NASH data showed 62% of patients in the 15 mg arm met criteria for MASH resolution without worsening of fibrosis vs 10% in placebo — a striking effect. The framework notes Phase 3 confirmatory trials are still in progress, but the Phase 2 magnitude justifies first-line positioning. The mechanistic story: tirzepatide's GIP receptor activation appears to drive hepatic lipid metabolism more effectively than GLP-1 monotherapy in MASH-affected livers.

The practical implication: if you have sleep apnea or known MASH, the algorithm pushes you toward Mounjaro (T2D) or Zepbound (obesity) rather than Ozempic or Wegovy. Whether your insurance will follow the algorithm is a separate fight.

The osteoarthritis case rests on the December 2024 STEP 9 trial: semaglutide produced 13.7% mean weight loss in patients with obesity and knee OA at 68 weeks plus a 41.7-point reduction in WOMAC pain score vs 28-point reduction on placebo. The pain-score effect is a substantive finding. Lilly's retatrutide TRIUMPH-4 trial in obesity + knee OA (28.7% weight loss + 75% pain reduction at 68 weeks) is mechanistically and quantitatively comparable, but retatrutide isn't approved yet; among approved agents at the time of the EASO evidence cutoff, semaglutide was the only one with positive OA trial data.

The cardiovascular case rests on SELECT, the landmark cardiovascular outcomes trial published in NEJM August 2023. Semaglutide reduced major adverse cardiovascular events by 20% in adults with established CVD and obesity. Tirzepatide doesn't have an equivalent completed CVOT (SURPASS-CVOT and SUMMIT are still running), so the framework appropriately reserves the first-line CVD recommendation for semaglutide until tirzepatide's CV data are in.

The MASH-fibrosis case is the narrowest of the three: among the agents with current evidence, only semaglutide has shown improvement in liver fibrosis staging at the time of the ESSENCE trial readout. Tirzepatide showed MASH resolution but not fibrosis improvement at the Phase 2 endpoint. The framework's nuance — semaglutide preferred for MASH-with-fibrosis, tirzepatide preferred for MASH-without — is the kind of detail that gets lost in summary coverage but matters clinically.

The framework deliberately stops short of pushing combination peptide therapy to first-line. CagriSema (cagrilintide + semaglutide) is under FDA review with an NDA filed December 2025. REDEFINE 1 produced 22.7% mean weight loss at week 68 — meaningfully more than semaglutide monotherapy, though short of the 25% internal target Novo set in early 2025. The May 12 body-composition data (35.7% fat mass loss vs 14.4% lean tissue loss) and May 14 cardiovascular sub-analyses (10.9 mmHg SBP reduction, 68.9% hsCRP drop) strengthen the combination case. But the framework defers a first-line recommendation until full CV outcomes data lands.

Retatrutide is even further behind in regulatory terms. The TRIUMPH program has produced TRIUMPH-4 (obesity + OA, 28.7% weight loss) and TRANSCEND-T2D1 toplines, but the NDA isn't expected before late 2026 or early 2027. The Phase 3 cardiovascular outcomes trial (TRIUMPH-OUTCOMES) is enrolling and won't read out for years.

The framework's implicit position: combinations and triple agonists are likely to displace single-agent first-line over the next 3-5 years, but until CV outcomes and head-to-head efficacy data land, the conservative recommendation is to anchor on the approved single agents. A defensible call. Patients who specifically want CagriSema or retatrutide today should expect to wait for label expansion or participate in late-phase trials.

Reading guideline documents requires noticing what's absent. The EASO algorithm doesn't address:

Cost or insurance coverage. The recommendation is clinically anchored. It doesn't acknowledge that a 70-year-old without diabetes who's been told to start Wegovy is often facing $1,300+/month out of pocket because Medicare Part D excludes weight-loss-only prescriptions. The Medicare GLP-1 Bridge (launching July 1, 2026 with $50/mo copay) partially addresses this, but eligibility is restricted to specific BMI + comorbidity profiles. The clinical recommendation is right; the access infrastructure to support it is incomplete.

Tolerance and discontinuation. Real-world persistence on anti-obesity GLP-1s is roughly 8% at three years per Prime Therapeutics commercial-claims data. The framework cites trial efficacy without engaging with the maintenance problem. A first-line algorithm that loses 92% of patients within three years isn't really a first-line algorithm; it's a sequence-of-care plan that needs a maintenance arm.

Sequencing and switching. If a patient starts on semaglutide for CV indication and gains 25 kg back after discontinuing, what does the framework recommend? Restart? Switch to tirzepatide? Step down to lower-dose maintenance? The SURMOUNT-MAINTAIN and ATTAIN-MAINTAIN Phase 3 publications from May 12 give specific maintenance data; the framework hasn't yet integrated them into its decision tree.

Geriatric and pediatric dosing. The 65+ data (Padova STEP pool, Lilly ATTAIN pool) was presented at the same ECO meeting but isn't reflected in the algorithm yet. Adolescent obesity (STEP TEENS, RESETTLE) is left for separate pediatric guidance.

Practical takeaways for an adult considering or already on a GLP-1:

If you have obstructive sleep apnea or MASH (or are at high risk for MASH given metabolic syndrome features), tell your prescriber the EASO framework supports tirzepatide as preferred first-line. Mounjaro for T2D, Zepbound for weight loss. This is the cleanest evidence-based case for choosing tirzepatide over semaglutide.

If you have established cardiovascular disease, knee osteoarthritis, or known liver fibrosis from MASH, the framework supports semaglutide as preferred. Wegovy or Ozempic depending on indication. The SELECT cardiovascular data and the STEP 9 OA data are both stronger than what's currently available for tirzepatide in these indications.

If you have type 2 diabetes, hypertension, or dyslipidemia without one of the differentiated complications above, both agents are acceptable first-line. The choice can default to access (insurance coverage), tolerability profile (tirzepatide tends to have slightly more dose-dependent GI effects at top doses), and patient preference on dosing convenience.

If you've been on an older agent (orlistat, naltrexone-bupropion, phentermine-topiramate) without adequate response, the framework supports stepping up to a GLP-1 unless there's a specific reason — pancreatitis history, family history of medullary thyroid carcinoma — that contraindicates incretins.

If cost is the binding constraint, the framework is silent. The practical sequence many patients face is: try the cheapest acceptable option first, escalate when access improves or budget permits.

EASO has framed the document as 'living guidance' that updates regularly. Several pieces of evidence from the last six months haven't yet been integrated:

The Lilly SURMOUNT-MAINTAIN (Lancet, May 12) and ATTAIN-MAINTAIN (Nature Medicine, May 12) maintenance trials — formal evidence for dose tapering and oral switching after maximum tolerated dose. The next update will likely add a maintenance arm to the algorithm.

Retatrutide TRIUMPH program (seven Phase 3 readouts due through 2026). If the cardiovascular outcomes data lands strongly, retatrutide could displace tirzepatide as first-line for several complications. The framework explicitly anticipates this; it just won't write the recommendation until the evidence is in.

CagriSema's regulatory decision. If FDA approves CagriSema in 2026 and the cardiovascular outcomes follow-on (REDEFINE-CVOT) reports positive data, combination therapy moves up the algorithm.

The orforglipron / oral GLP-1 question. Foundayo is approved but isn't yet integrated into the framework. The next update will need to address whether oral GLP-1s sit alongside injectable GLP-1s as first-line, or whether they're appropriately reserved for patients who can't tolerate or access injectables.

The broader question the framework doesn't yet answer: how long should patients stay on these drugs? The maintenance question is the field's largest unresolved clinical issue, and the next iteration of EASO guidance will probably take a clearer position. Right now the algorithm tells you what to start; it doesn't tell you when, or if, to stop.