GLP-1 Peptides Explained: Semaglutide, Tirzepatide & Retatrutide

The class of peptides that's reshaping obesity treatment — what they do, how they differ, and what to expect.

What is GLP-1?

GLP-1 (glucagon-like peptide-1) is a hormone your gut releases after eating. It tells your pancreas to release insulin, slows stomach emptying, and signals fullness to your brain.

The major players

Semaglutide (Ozempic, Wegovy)

Single agonist (GLP-1 only). Weekly injection. Average weight loss: ~15% of body weight over 68 weeks.

Tirzepatide (Mounjaro, Zepbound)

Dual agonist (GLP-1 + GIP). Weekly. Average weight loss: ~20-22%.

Retatrutide

Triple agonist (GLP-1 + GIP + glucagon). Still in trials. Phase 2 data showed ~24% weight loss at 48 weeks — the most powerful of the three.

Side effects to know

Nausea (especially in the first 4 weeks)
Constipation or diarrhea
Fatigue
Loss of appetite (this is the point, but can become excessive)
Rare: pancreatitis, gallbladder issues

Titration matters

Starting at the lowest dose and slowly increasing every 4 weeks dramatically reduces side effects. Don't skip the ramp.