Semaglutide: The Complete Science Guide 2026 (SELECT, FLOW, STEP-HFpEF, SOUL, EVOKE)

Semaglutide is the most extensively studied GLP-1 receptor agonist in medicine. Marketed as Ozempic for type 2 diabetes and as Wegovy for obesity, the molecule anchors nearly every modern debate in metabolic therapeutics. It is also the reference compound against which every newer incretin, including tirzepatide and the triple agonist retatrutide, is now measured.

This guide consolidates the decisive trials from 2023 through 2025 that defined semaglutide's place in the evidence base: SELECT for cardiovascular prevention, FLOW for kidney protection in diabetes, STEP-HFpEF for heart failure with preserved ejection fraction, SOUL as the first oral GLP-1 cardiovascular outcomes trial, and the notable failure of EVOKE and EVOKE+ in Alzheimer disease. It closes with the 2026 context: where semaglutide stands now that head-to-head data and triple agonists have reshaped the landscape.

Background: What Semaglutide Is and Why It Matters

Semaglutide is a long-acting analogue of glucagon-like peptide-1 (GLP-1), an incretin hormone released by enteroendocrine L-cells after meals. Native GLP-1 has a plasma half-life of roughly two minutes. Semaglutide extends this to about one week through two key modifications: a C18 fatty acid side chain that promotes reversible albumin binding, and substitutions that resist degradation by dipeptidyl peptidase-4 (DPP-4).

The molecule was approved by the FDA in December 2017 for type 2 diabetes as Ozempic. In June 2021, a higher-dose formulation (2.4 mg weekly) received approval as Wegovy for chronic weight management in adults with obesity or overweight plus comorbidity. An oral tablet formulation, Rybelsus, followed for diabetes in 2019 and for cardiovascular risk reduction in 2025.

The pharmacology is dense but consistent. At the GLP-1 receptor, semaglutide enhances glucose-dependent insulin secretion, suppresses glucagon release, slows gastric emptying, and acts on hypothalamic and brainstem circuits that regulate appetite. These combined actions drive both glycemic improvement and substantial weight loss. The question that dominated the field from 2020 onward was whether the downstream effects translated into hard clinical outcomes beyond surrogate markers. The trials that follow answered that question.

Cardiovascular Outcomes: The SELECT Trial (2023)

Before SELECT, the cardiovascular evidence for GLP-1 agonists came largely from type 2 diabetes populations. SELECT was the first dedicated cardiovascular outcomes trial (CVOT) in adults with overweight or obesity without diabetes.

SELECT was the trial that moved semaglutide from a weight-loss and glycemic drug to a cardiovascular prevention drug in its own right. The benefit emerged early and diverged progressively, and it was not explained entirely by the degree of weight loss, suggesting mechanistic effects beyond body composition. Reductions in systolic blood pressure, inflammatory markers, and lipid parameters likely contributed. The FDA subsequently expanded the Wegovy label in March 2024 to include cardiovascular risk reduction in adults with overweight or obesity and established disease.

SELECT remains the single most cited trial for GLP-1 cardiovascular benefit and the reference point newer agents must match or exceed.

Kidney Protection: The FLOW Trial (2024)

FLOW examined whether semaglutide slows progression of chronic kidney disease in people with type 2 diabetes. The trial was stopped early by the data and safety monitoring board because efficacy met prespecified thresholds.

FLOW was significant not only for the magnitude of effect but for the speed at which it accumulated. The trial's early termination meant that practice guidance in both nephrology and diabetes had to be updated within months. Semaglutide joined SGLT2 inhibitors and non-steroidal mineralocorticoid antagonists as a foundational therapy in diabetic kidney disease. The mechanism likely involves weight loss, glycemic improvement, blood pressure reduction, and direct anti-inflammatory and antifibrotic effects on renal tissue.

Heart Failure: STEP-HFpEF and STEP-HFpEF DM

Heart failure with preserved ejection fraction (HFpEF) has historically been a therapeutic orphan. Diuretics ease congestion, but few agents improve hard outcomes or patient-reported symptoms. Obesity is present in roughly 80 percent of HFpEF patients. Two STEP-HFpEF trials tested whether targeting obesity itself could reshape the disease course.

The KCCQ-CSS improvement was larger than that seen with almost any prior HFpEF intervention. Exercise capacity on the 6-minute walk test increased meaningfully. The signal held up in the companion trial that enrolled patients with diabetes.

Together, the two trials established that in the obesity-HFpEF phenotype, semaglutide produces symptomatic and functional improvements consistent across the diabetic and non-diabetic populations. The magnitude of symptom change is now a reference for subsequent HFpEF trials. Pooled analyses have also signalled favourable trends on heart failure hospitalisations, a hard endpoint that dedicated event-driven trials will need to confirm.

Oral Semaglutide and Cardiovascular Outcomes: The SOUL Trial (2025)

SOUL answered a practical question that had lingered for years. Injectable semaglutide had SELECT for cardiovascular prevention and FLOW for renal protection. But many patients prefer oral therapy. Would the oral tablet formulation deliver comparable cardiovascular benefit?

SOUL is the first cardiovascular outcomes trial of any oral GLP-1 agent. The effect size is smaller than SELECT, reflecting the different population and the challenges of maintaining GLP-1 exposure with an oral formulation that has variable absorption. Nonetheless, the result validated oral semaglutide as a legitimate cardiovascular therapy and opened a route for patients who decline or cannot tolerate injections.

Off-Label Signals: Alcohol Use Disorder

Anecdotal reports since 2022 suggested that patients on semaglutide for diabetes or obesity also reduced alcohol consumption. A 2025 Phase 2 randomised trial formalised the question.

This was the first well-controlled trial in humans to show that GLP-1 agonism modulates alcohol consumption. The effect size matched or exceeded currently approved medications for alcohol use disorder. Larger Phase 3 studies are planned. The trial suggests that semaglutide acts on shared reward circuitry linking food and substance intake, a hypothesis supported by preclinical work in the ventral tegmental area and nucleus accumbens.

What Did Not Work: The EVOKE Alzheimer Trials (2025)

Observational data and mechanistic plausibility had suggested that GLP-1 agonists might slow cognitive decline. Semaglutide crosses the blood-brain barrier minimally, but effects on vascular risk factors, inflammation, and insulin signalling made Alzheimer disease a reasonable target. Novo Nordisk ran two Phase 3 trials, EVOKE and EVOKE+, in early Alzheimer disease.

In late 2025, the trials read out negative. Oral semaglutide did not slow cognitive decline on the CDR-SB (Clinical Dementia Rating Sum of Boxes) compared to placebo. The programme was discontinued.

The failure has implications beyond Alzheimer disease. It suggests that the central nervous system effects of peripheral semaglutide are either insufficient to alter neurodegenerative pathology or that existing amyloid-driven disease has already passed beyond the point where metabolic tailwinds help. It also reinforces the general lesson that plausible mechanisms do not guarantee clinical benefit without a dedicated trial.

2026 Context: Where Semaglutide Sits Now

The 2023-2025 data transformed semaglutide from a diabetes and obesity drug into a multi-organ therapy. But the field has not stood still. Two developments now shape how semaglutide is positioned in 2026.

Head-to-head weight loss data. SURMOUNT-5 (Aronne et al., NEJM 2025, PMID 40353578) compared tirzepatide and semaglutide directly for obesity. Over 72 weeks, tirzepatide at maximum tolerated dose achieved 20.2% mean weight reduction versus 13.7% for semaglutide 2.4 mg, a statistically and clinically significant difference (p less than 0.001). The trial established that dual agonism (GLP-1 plus GIP) produces more weight loss than GLP-1 alone in a population without diabetes.

Triple agonism has arrived. Retatrutide, a GLP-1/GIP/glucagon triple agonist, delivered 28.7% mean weight loss in the TRIUMPH-4 Phase 3 trial at 68 weeks. This is roughly double the weight loss of semaglutide in comparable populations, with an associated 75.8% improvement in WOMAC pain scores among patients with knee osteoarthritis. For pure weight loss, retatrutide now sets the bar.

What semaglutide still owns is depth of outcomes evidence. Newer agents have weight loss superiority, but semaglutide has SELECT for cardiovascular events, FLOW for kidney composite outcomes, STEP-HFpEF for heart failure symptoms, and SOUL as the first oral GLP-1 CVOT. Until tirzepatide's SURPASS-CVOT and retatrutide's TRANSCEND-CKD and cardiovascular outcomes trials report, semaglutide remains the reference for hard clinical endpoints beyond weight and glycemia.

The practical implication is that the field is stratifying. For maximum weight loss, triple agonism wins. For cardiovascular event prevention with the deepest evidence base, semaglutide holds. For kidney protection in type 2 diabetes, semaglutide is backed by FLOW. For HFpEF symptoms in obesity, STEP-HFpEF data drive practice. The next three years of readouts will show whether newer molecules match semaglutide's breadth or whether the reference position holds.

Summary and Where the Research Is Going

Semaglutide's 2023-2025 arc is one of the most consequential runs any metabolic drug has had. SELECT converted a weight and glucose agent into cardiovascular prevention. FLOW added kidney protection. STEP-HFpEF opened a route into heart failure. SOUL extended outcomes evidence to the oral formulation. Alcohol use disorder gained its first randomised signal. And EVOKE showed honestly that plausible hypotheses can fail.

For researchers following the incretin landscape in 2026, the current frontier sits one step beyond semaglutide. Retatrutide, the triple agonist, now delivers the strongest weight loss data in the literature, with TRIUMPH-4 Phase 3 results establishing a new benchmark. For a detailed analysis of the TRIUMPH-4 readout and the positioning of triple agonism against semaglutide and tirzepatide, see the Retatrutide TRIUMPH-4 study results article.

Semaglutide's evidence base is not going away. But the science is moving, and the next generation of trials will determine whether the reference role stays where it is or shifts to the multi-receptor agonists that emerged in its wake.