GLP-1 Receptor Agonists: The 3-Receptor Ladder

Start with the plain-language version. Your gut already makes hormones that tell your brain and pancreas “food has arrived” — these are called incretins. GLP-1 is the most famous one. An agonist is simply a drug that fits the same lock and turns the same key as the natural hormone, only far longer-lasting. That is the entire trick: copy a hormone your body already trusts, and make it stick around for a week instead of a couple of minutes.

The whole class is built from three gut-hormone receptors. A drug can hit one, two, or all three. Here is the job each receptor does, why adding more of them compounds the weight loss — and, honestly, the counter-intuitive one. Glucagon normally raises blood sugar, so putting it in a weight-loss drug sounds backwards; at these doses its dominant effect is to make the body burn more energy, not to spike glucose. More levers is not automatically better, though: each receptor is also one more place for a side effect to come from.

This is the headline structure of the whole class. Semaglutide hits one receptor. Tirzepatide hits two. Retatrutide hits three. As each receptor was added, average weight loss climbed — roughly a doubling from the single agonist to the (claimed) triple. Read the chart with one honest caveat in mind: the first two bars are peer-reviewed, published, FDA-approved numbers; the third bar is Eli Lilly's own unreviewed press-release figure. A taller bar built on a weaker evidence base is exactly the thing this page wants you to see, not gloss over.

The class in one table — which receptors each drug hits, whether it is actually approved, the headline trial and its weight-loss number, and what it is sold as. Two of these are on pharmacy shelves today; the third is not. Each drug also has its own full page on this site — linked at the bottom.

Every drug on this ladder shares a trade-off the weight-loss percentage does not show you: a meaningful share of the weight lost is lean mass — muscle — not just fat. This comes straight from the drugmakers' own body-composition (DEXA) scans and from independent reviewers who take no pharma money. It is not a reason to dismiss the class; it is a reason to lift weights and eat enough protein while on it.

Every approved drug in this class carries the same FDA boxed warning — the strongest warning the FDA issues. It is worth reading the label's own words rather than a summary, because the precise version matters: the tumor finding is in rodents, and the label itself says the human relevance is not established. That is neither “proven to cause cancer” nor “nothing to see here.” It is a real, unresolved signal with a hard contraindication attached.

The evidence on this ladder is real — and it is also almost entirely generated by the two companies that sell the drugs. That is not a conspiracy claim; it is the plain business reality behind every number on this page. Know who is telling you the number, and what they stand to gain.

A class overview owes you the money reality, because on these drugs “approved” and “affordable” are different words. Weight tends to return when people stop, so the real cost is the cost of staying on — indefinitely. Only about a dozen US states mandate insurance coverage for obesity-indication GLP-1 drugs, and employers have been dropping it as prices climb.

This page explains the idea. Each drug on the ladder has its own full evidence page — trials, dosing, cost, side effects, and a dose calculator where relevant.