Same mechanism, different number of receptors. What that changes, and what it does not.
Semaglutide, Tirzepatide and Retatrutide all work through the same broad mechanism — mimicking gut hormones that regulate appetite and blood sugar. They differ in how many receptors they hit, and that difference is real.
GLP-1 is a hormone your gut releases after eating. It slows gastric emptying, increases satiety signalling, and improves glucose response. A GLP-1 agonist mimics it, so you feel full sooner and stay full longer.
GIP is a second incretin hormone. Glucagon is a third pathway, mostly associated with energy expenditure.
More receptors does not automatically mean better. It means more effect and generally more side effects.
The benchmark. Single receptor, roughly seven-day half-life, weekly dosing. It is the best-characterised of the three because it has been in clinical use longest.
Strong appetite suppression. Cheapest per mg of the three. If you want the known quantity, this is it.
Adds the GIP receptor. In practice that means stronger appetite suppression and, for most people, more effect per mg.
Roughly five-day half-life, still weekly dosing. For many people this is the sweet spot: noticeably stronger than semaglutide without the third pathway.
Triple agonist. The glucagon component is what makes it different — it appears to increase energy expenditure rather than only reducing intake.
Around a six-day half-life, weekly dosing. The most aggressive of the three, and the one with the least long-term data behind it. That is the trade.
| Semaglutide | Tirzepatide | Retatrutide | |
|---|---|---|---|
| Receptors | GLP-1 | GLP-1 + GIP | GLP-1 + GIP + glucagon |
| Half-life | ~7 days | ~5 days | ~6 days |
| Frequency | Weekly | Weekly | Weekly |
| Appetite suppression | Strong | Stronger | Strongest |
| Evidence base | Largest | Large | Smallest |
All three are titrated up slowly. Starting at a full dose is the most common mistake.
Start low, hold two to four weeks, increase only if side effects have settled and appetite is returning. Going up faster than your gut adapts is how people end up nauseous for a week.
Nausea, burping, reflux, constipation, and early satiety that overshoots into not wanting food at all. Most settle within two weeks of a given dose.
Management: smaller meals, more protein, more water, and patience. Titrate slower if you need to.
This gets under-discussed. Rapid weight loss takes muscle with it unless you defend it.
Consider stacking with a growth hormone secretagogue or Growth if muscle retention is the priority.
Want the known quantity, cheapest per mg: semaglutide.
Want stronger effect without a third pathway: tirzepatide.
Want maximum effect and accept less data: retatrutide.
Whichever you choose, give it 8-12 weeks at a settled dose before judging it. Switching compounds every month tells you nothing.
All three are lyophilized. Reconstitute with bacteriostatic water, keep reconstituted vials in the fridge, and use within 4-6 weeks.
Retatrutide, as a triple agonist. Tirzepatide is next, then semaglutide.
Semaglutide, by a wide margin. It has been in clinical use longest.
Low dose, hold two to four weeks, titrate up only once side effects settle.
Not if you eat enough protein and train. Rapid weight loss takes muscle with it otherwise.