GLP-1 Beyond Weight: What the Outcome Trials Actually Show

Surrogate endpoints are how drug development moves quickly. Outcome endpoints are how medicine decides what a drug is worth. In the incretin literature, both exist, and they do not carry the same weight.

An outcome trial asks whether fewer people had heart attacks, strokes, hospitalisations for heart failure or progression to kidney failure. That question takes years, thousands of participants and pre-specified statistical rules that cannot be reinterpreted after the fact.

Why outcome trials are read less

They are harder to summarise. A percentage of body weight is intuitive; a hazard ratio on a composite endpoint is not. Secondary coverage therefore tends to reach for the weight figure even when the study in question measured something else entirely.

The practical consequence is a public conversation in which a cardiovascular finding and a cosmetic one are quoted in the same breath, as if they were the same class of evidence.

Composite endpoints deserve unpacking

Most cardiovascular outcome trials use a composite: cardiovascular death, non-fatal myocardial infarction, non-fatal stroke. A positive composite does not mean every component moved. Reading the component breakdown is the difference between knowing a result and repeating it.

The same applies to kidney composites, which frequently blend a sustained fall in estimated filtration rate with dialysis initiation and renal death — events of very different severity and frequency.

What still is not known

Duration is the open question. Outcome trials run for years, not decades, and people with obesity or type 2 diabetes may use these agents far longer than any trial has followed anyone.

There is also little head-to-head outcome evidence between agents in the class. Ranking them on cardiovascular benefit from separate trials with different populations is inference, not comparison.