Semaglutide vs tirzepatide vs retatrutide

What is the difference between semaglutide, tirzepatide and retatrutide?

Short answer: they are three generations of incretin-based peptides. Semaglutide activates one receptor (GLP-1), tirzepatide two (GIP and GLP-1) and retatrutide three (GIP, GLP-1 and glucagon). Semaglutide and tirzepatide are approved prescription medicines in Thailand; retatrutide is still investigational. In SURMOUNT-5, the first head-to-head obesity trial, tirzepatide produced a larger mean reduction in body weight than semaglutide.

All three are long-acting, once-weekly molecules in their clinical programmes, made long-lived by a fatty acid side chain that binds albumin in the blood.

How do they compare side by side?

What did the head-to-head trials show?

Two trials compared tirzepatide directly with semaglutide:

• SURPASS-2 (2021), in adults with type 2 diabetes, compared tirzepatide with semaglutide 1 mg; the primary endpoint was HbA1c, a long-term blood glucose marker.
• SURMOUNT-5 (2025), an open-label phase 3b trial in adults with obesity but without diabetes, compared the two over 72 weeks. Tirzepatide produced a larger mean percentage reduction in body weight and waist circumference.

No trial has yet compared retatrutide head to head with either, as far as we know. Comparing numbers across separate trials is unreliable, because populations, durations and protocols differ. Gastrointestinal events such as nausea were the most common adverse events for all three; the papers below carry the full safety data.

Why add GIP and glucagon receptors?

GLP-1 receptor activity is the common core. Adding GIP receptor activity, as tirzepatide does, was once counterintuitive, because GIP alone has weak effects in type 2 diabetes; research since suggests the combination acts differently on adipose tissue and the brain than either hormone alone. Retatrutide adds glucagon receptor activity, studied for its effects on energy expenditure and hepatic lipid metabolism. Whether each extra receptor changes the balance of benefit and risk is exactly what the phase 3 programmes are testing. Our retatrutide vs tirzepatide guide goes deeper on the receptor profiles.

Which ones are available in Thailand?

Semaglutide and tirzepatide medicines are registered in Thailand and, since 15 September 2026, GLP-1 pen medicines are specially controlled drugs: a doctor's prescription, dispensed by a pharmacist. Retatrutide is not registered anywhere, so it is not available as a medicine; our retatrutide guide covers the published research, and our Mounjaro price guide for prescription costs in Bangkok.

What does Friday stock?

Friday does not sell semaglutide or any prescription medicine. It stocks research-grade tirzepatide (10mg (฿1,890) and 20mg (฿3,460) vials) and retatrutide (10mg (฿3,190) and 20mg (฿5,790) vials), plus cagrilintide, an amylin analogue studied in the same research area, all on the catalogue. Third-party tested. Research use only. Orders are packed in Bangkok and leave with tracking the next working day, to any address in Thailand. Delivery is a flat ฿60, prices are in Thai baht, and payment is by bank transfer with a slip that our team confirms before dispatch.