Liraglutide vs Semaglutide
An evidence-first, side-by-side comparison. We compare what the research supports — not marketing claims.
Last updated
Evidence grade
Human RCT
Human RCT
What that means
Randomized controlled trials in humans — the strongest evidence we grade.
Randomized controlled trials in humans — the strongest evidence we grade.
Status
Prescription
FDA-approved
Mechanism
Liraglutide is a GLP-1 receptor agonist, the same basic mechanism as semaglutide — it slows gastric emptying, acts on hypothalamic appetite centers to reduce intake, and enhances glucose-dependent insulin release. The difference is pharmacokinetic: a shorter half-life means once-daily rather than once-weekly injection. It was the GLP-1 that first carried this mechanism into approved weight management, which is why it matters historically even though the newer molecules hit the receptor (and, for tirzepatide, a second receptor) more effectively.
Semaglutide is a long-acting GLP-1 receptor agonist. It mimics the gut incretin hormone GLP-1: slowing gastric emptying, acting on appetite centers in the hypothalamus to reduce hunger and food intake, and enhancing glucose-dependent insulin secretion. The appetite effect is the one that drives the weight loss — people simply eat less and feel full sooner. Structural modifications (a fatty-acid chain that binds albumin) give it a long enough half-life for once-weekly injection, and an oral formulation (Rybelsus) exists for the diabetes indication.
Weight-loss data
Mean ~8% body-weight reduction at 3.0 mg/day over 56 weeks (SCALE, Pi-Sunyer 2015)
Mean ~14.9% body-weight reduction at 2.4 mg/week over 68 weeks (STEP 1, Wilding 2021)
Goals
Fat loss, Body composition
Fat loss, Body composition, Visceral fat reduction
Key risks
- Boxed warning: GLP-1 agonists caused thyroid C-cell tumors in rodents; contraindicated in personal or family history of medullary thyroid carcinoma (MTC) or MEN 2
- GI effects (nausea, vomiting, diarrhea) are common, particularly during titration
- Reports of acute pancreatitis; discontinue if suspected
- Boxed warning: in rodents, GLP-1 agonists caused thyroid C-cell tumors; contraindicated in personal or family history of medullary thyroid carcinoma (MTC) or MEN 2. Human relevance is unestablished but the contraindication stands
- GI effects are very common: nausea, vomiting, diarrhea, constipation — usually dose-dependent and worst during dose escalation
- Reports of acute pancreatitis; discontinue if suspected
Regulatory
Available in the US only via prescription or a compounding pharmacy.
Approved by the FDA for one or more human indications.