Systematic Review: GLP-1 Receptor Agonists and Co-Agonists Facilitate Significant Weight Loss in Adults Without Diabetes

Background: Obesity is increasingly treated as a chronic disease requiring long-term management. Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) were originally developed for type 2 diabetes but subsequently demonstrated substantial weight loss benefits in individuals with overweight or obesity. Although several GLP-1 RAs and related dual or triple co-agonists have been assessed in diverse populations, their overall efficacy and safety profile among adults without diabetes had not been thoroughly evaluated.

Objective: To systematically appraise the efficacy and safety of GLP-1 RAs (including single, dual, and triple agonists) for weight loss in otherwise healthy adults with overweight or obesity and without diabetes.

Methods: Investigators searched MEDLINE, Embase, and Cochrane CENTRAL through 4 October 2023 for placebo-controlled randomized controlled trials (RCTs). Eligible studies enrolled adults with body mass index (BMI) ≥27 kg/m^2 (plus one weight-related comorbidity) or ≥30 kg/m^2, in the absence of diabetes or other major diseases. Trials had to last at least 16 weeks and report changes in body weight and safety outcomes. The primary endpoint was percent or absolute change in body weight from baseline. Safety assessments included adverse events (AEs), serious AEs (SAEs), and gastrointestinal (GI) events.

Results: Twenty-six RCTs encompassing 15,491 participants (72% female; mean BMI range, 30–41 kg/m^2; mean age range, 34–57 years) evaluated 12 agents. Three drugs (liraglutide, semaglutide, tirzepatide) are commercially available for weight management; nine are premarket (e.g., retatrutide, orforglipron, mazdutide). Treatment periods ranged from 16 to 104 weeks (median, 43 weeks). Across studies, GLP-1 RAs and co-agonists consistently demonstrated significant weight reductions compared with placebo. Tirzepatide (15 mg weekly) reached up to a 17.8% (95% CI, 16.3% to 19.3%) weight reduction after 72 weeks, whereas semaglutide (2.4 mg weekly) achieved up to 13.9% (95% CI, 11.0% to 16.7%) after 68 weeks. Liraglutide produced more modest losses of up to 5.8% (95% CI, 3.6% to 8.0%) after 26 weeks. Novel agents, particularly the triple agonist retatrutide (12 mg weekly), reported greater average weight losses of up to 22.1% (95% CI, 19.3% to 24.9%) after 48 weeks. Although AEs were often very common (GLP-1 RA vs. placebo: 80%–97% vs. 63%–100%), most were GI-related (47%–84% vs. 13%–63%) and mild or moderate. Importantly, only a smaller proportion of participants (0%–26% vs. 0%–9%) discontinued treatment due to AEs, and SAEs (0%–10% vs. 0%–12%) occurred at relatively lower rates overall. While select SAEs of interest, including severe GI events, biliary disorders, pancreatitis, and psychiatric disorders, were inconsistently reported, they were generally rare (severe GI and biliary disorders, ≤3.5%; pancreatitis, <2%; psychiatric disorders, ≤15% [including less severe events, such as insomnia and mood alterations]).

Conclusions: GLP-1 RAs and co-agonists appear highly efficacious for weight reduction in adults without diabetes, with GI events as the principal safety concern. Among emerging agents, retatrutide in particular has shown even greater efficacy, though further research is needed to clarify comparative effectiveness, costs, and real-world feasibility.

Implications for Practice: Clinicians considering GLP-1 RAs or dual and triple co-agonists for obesity treatment should monitor for GI side effects and counsel patients about long-term use to sustain weight loss. As these newer treatments often come with higher price points and uncertain insurance coverage, cost-effectiveness and sponsor bias should be weighed. Careful patient selection, ongoing monitoring, and discussion of adherence requirements are critical to optimize outcomes in real-world practice.

Study Strengths and Limitations: This review incorporated RCTs with substantial sample sizes and used predefined inclusion criteria focused on healthy adults without diabetes, ensuring a clearer understanding of weight-loss outcomes in this group. However, head-to-head comparisons among agents were lacking, and heterogeneity in trial designs (varying lifestyle interventions, follow-up durations, and dose-escalation approaches) precluded meta-analysis of pooled data. Reporting of specific adverse outcomes was also inconsistent.

Future Research: Larger, longer-term head-to-head RCTs are warranted to evaluate comparative effectiveness, durability of weight loss, and cost implications. Investigations should also explore safety beyond GI events, including rare but serious outcomes such as thyroid disease, gallbladder disorders, or pancreatitis, and determine whether combination therapies (e.g., cagrilintide–semaglutide) confer added benefits.

Reference: Moiz A, Filion KB, Toutounchi H, Tsoukas MA, Yu OHY, Peters TM, Eisenberg MJ. Efficacy and Safety of Glucagon-Like Peptide-1 Receptor Agonists for Weight Loss Among Adults Without Diabetes: A Systematic Review of Randomized Controlled Trials. Annals of Internal Medicine. DOI: https://doi.org/10.7326/ANNALS-24-01590