How tirzepatide works: GIP vs GLP‑1 explained (and why ‘dual’ matters)

Tirzepatide is often described as a “dual incretin” medicine because it activates two hormone pathways involved in appetite and glucose regulation: GIP and GLP‑1.

The short version

• GLP‑1 helps regulate appetite, slows gastric emptying, and improves glucose control.
• GIP also influences insulin response and appetite signalling, in ways researchers continue to map.
• By targeting both, tirzepatide can produce strong average effects on weight and glucose in clinical trials.

Why people feel less hungry

Many people notice earlier fullness, fewer cravings, and a quieter ‘food noise’ effect. That makes it easier to sustain a calorie deficit without white‑knuckling hunger.

Why side effects happen

Because these pathways affect the gut and stomach emptying, nausea, constipation, and diarrhoea are common, particularly when starting or increasing the dose. This is why titration matters.

Not a magic switch

The best outcomes usually come from combining medication with nutrition, activity, and follow‑up. Medication helps you do the work, it doesn’t replace it.

Sources

• Medsafe data sheet: Mounjaro (tirzepatide mechanism and dosing)
• SURMOUNT‑1 summary — American Diabetes Association