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The GLP-1 category is the most asked-about and the most oversimplified. Most comparisons line up three weight-loss percentages and call it a ranking, but those numbers come from three separate trials with different populations, durations, and designs, so they were never a clean head-to-head. This lays out what each compound is, what its own trial showed, and where the only real direct comparison actually exists.

For research and educational purposes only. Not medical advice.

The one thing to understand first

Receptor count is the real story. Each of these adds a target on the same GLP-1 backbone, and efficacy climbs roughly in step.

Compound	Receptor targets	Class
Semaglutide	GLP-1	Single agonist
Tirzepatide	GLP-1 + GIP	Dual agonist
Retatrutide	GLP-1 + GIP + glucagon	Triple agonist

Semaglutide and tirzepatide are FDA approved. Retatrutide is Phase 3, investigational, and not approved.

What each trial actually showed

These are the headline figures, each from that compound's own pivotal trial. They read as separate results, not a finish line.

Compound	Trial	Weight loss	Duration	Top dose
Semaglutide	STEP 1	14.9%	68 wks	2.4 mg
Tirzepatide	SURMOUNT-1	~20.9%	72 wks	15 mg
Retatrutide	TRIUMPH-1	28.3%	80 wks	12 mg

The trend tracks receptor count: single agonist around 15%, dual around 21%, triple around 28%. The populations and durations differ across the three trials, though, so treat the gaps as directional rather than exact.

The only true head-to-head

One direct comparison exists. Everything else is cross-trial.

SURMOUNT-5 put tirzepatide against semaglutide in the same trial: over 72 weeks in people with obesity and no diabetes, tirzepatide reached 20.2% versus semaglutide at 13.7%. Same trial, same population, same timeframe, which makes it the cleanest evidence that the dual agonist outperforms the single. There is no equivalent trial yet placing retatrutide directly against either, so its 28% sits on its own data, not a head-to-head win. The pending TRANSCEND-T2D-2 trial, retatrutide against semaglutide, is the readout that would change that.

Mechanism, in plain terms

Semaglutide works the GLP-1 pathway alone: it slows gastric emptying, boosts insulin secretion, suppresses glucagon, and reduces appetite. One pathway, worked thoroughly, and it's the most studied and prescribed of the three.

Tirzepatide adds GIP to that GLP-1 action. The GIP component appears to improve both appetite signaling and how the body handles nutrients, and the combined action delivers stronger appetite suppression and glucose control than single agonism does.

Retatrutide stacks a third receptor, glucagon, on top of tirzepatide's two. The glucagon arm raises energy expenditure and drives liver-fat reduction, which is the mechanistic reason it pushes toward 30% weight loss and posts large liver-fat numbers in its trials. It is also the least proven on long-term safety, since it's the earliest in development.

Side effects: the shared reality

All three are gastrointestinal-dominant: nausea, vomiting, diarrhea, constipation, mostly transient and dose-related. A few trial specifics:

• Retatrutide carried the highest GI adverse-event rate at its top doses, alongside the strongest efficacy. A dysesthesia signal (altered sensation) showed up in the data and is still being characterized.
• All three show substantial weight regain when stopped. That's a class trait, not specific to any one.
• Pancreatic enzyme monitoring (amylase, lipase) applies across the class, with the meaningful threshold being a large elevation plus symptoms, not a minor bump.

The honest bottom line

The receptor-count trend is real, and the one direct comparison that exists supports it: more targets, more weight loss, up the line. But two of the three headline numbers come from separate trials, only two of the three are approved, and the most impressive figure on the board, retatrutide's, is also the least proven for long-term safety. The compound with the best trial number is not automatically the right tool for a given context, and "investigational" is carrying weight in that sentence.

The open question

For anyone tracking this space: how much does the missing head-to-head matter. Retatrutide's 28% is from its own trial, never run directly against tirzepatide, and the comparison that would settle it (TRANSCEND-T2D-2) hasn't reported. Curious whether people read the receptor-count trend as strong enough to call the order now, or whether the lack of a direct retatrutide comparison leaves it genuinely open.

Hoping to share knowledge locally🙂