The science behind GLP-1: Why tirzepatide & semaglutide actually work

For decades, sustainable weight loss felt out of reach for most people. Calorie restriction worked — until the body adapted. Exercise helped — until appetite caught up. The arrival of GLP-1 receptor agonists has fundamentally changed that equation.

How GLP-1 rewires appetite

GLP-1 is a gut hormone your body releases after eating. It signals fullness to the brain, slows gastric emptying, and improves insulin response. Semaglutide and tirzepatide are long-acting mimics — one weekly injection keeps that 'I've eaten enough' signal active all week long.

Why tirzepatide goes further

Tirzepatide adds a second hormone target — GIP — that amplifies the effect on appetite and fat storage. Clinical trials show up to 22.5% body weight loss over 72 weeks, the largest reduction of any FDA-approved medication to date.

What members typically see

Most Rejuviya members notice reduced food noise within the first week, visible weight loss by week 4–6, and steady progress through months 3 to 6. The dose is titrated slowly to minimize nausea and protect long-term tolerability.