Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) have transformed type 2 diabetes treatment over the past five years. Drugs such as semaglutide, tirzepatide, and the emerging retatrutide not only control blood glucose but also reduce cardiovascular events, slow kidney disease progression, and produce weight losses of up to 20% of body weight. In 2026, the type 2 diabetes treatment algorithm is being rewritten.
Mechanism of action and differences between molecules
GLP-1 receptor agonists act on the GLP-1 receptor, present in the pancreas, brain, gastrointestinal tract, and myocardium. Activation produces four main effects: glucose-dependent insulin secretion stimulation, glucagon suppression, gastric emptying delay, and appetite reduction at the hypothalamic level.
Weekly subcutaneous semaglutide (Ozempic) is currently the class standard. Tirzepatide (Mounjaro) adds agonism on the gastric inhibitory polypeptide receptor (GIP), amplifying weight loss and glycemic control. The SURPASS-5 trials demonstrate HbA1c reductions of up to 2.3% and weight losses of 12-15% with tirzepatide 15 mg.
Retatrutide, in advanced clinical trials in 2026, combines triple agonism on GLP-1, GIP, and glucagon, with 24% weight loss over 48 weeks in the phase 2 trial published in The New England Journal of Medicine.
Cardiovascular and renal benefits
The SELECT trial, published in 2023 with follow-up extended to 2025, demonstrated that semaglutide 2.4 mg weekly reduces major adverse cardiovascular events (MACE) by 20% in obese patients with established cardiovascular disease but no diabetes. This finding has led guidelines to recommend GLP-1 RAs not just for glycemic effect but as cardioprotective agents.
In the renal domain, the FLOW trial with semaglutide has for the first time in this drug class demonstrated a significant reduction in progression to end-stage renal disease, with a 24% decrease in the composite renal endpoint.
Updated 2026 treatment algorithm
The ADA and EASD published a joint consensus update in January 2026. The most significant changes:
- First line: metformin remains the initial drug, but early addition of a GLP-1 RA or SGLT-2 inhibitor is recommended for obesity or high cardiovascular risk, even with controlled HbA1c.
- Established cardiovascular disease: a GLP-1 RA (preferably semaglutide or liraglutide) or SGLT-2 inhibitor is recommended regardless of glycemic control.
- Heart failure or CKD: SGLT-2 inhibitor is prioritized given stronger evidence in these settings.
- Obesity with diabetes: tirzepatide is the preferred option for its greater weight loss.
Adverse effects and practical considerations
The most frequent adverse effects are gastrointestinal: nausea (20-40%), vomiting (10-15%), and diarrhea (10-15%), generally transient and related to dose titration. Slow dose escalation (4-8 weeks per step) significantly reduces digestive intolerance.
Hypoglycemia risk is minimal in monotherapy but increases when combined with sulfonylureas or insulin. The cost barrier remains significant — access to these drugs for obesity without diabetes varies considerably across healthcare systems in Europe.
