Reading time: ~2 min · Part of the free certification in peptide science
Not all studies are worth the same. Knowing which rung the evidence for a compound is on is the most useful skill in this course, because most of the literature on research peptides sits on the lowest rungs.
In vitro
Isolated cells or enzymes. Useful for mechanisms; it says nothing about dose, distribution or effect in an organism.
Animal models
They integrate pharmacokinetics and physiology, but with species differences, per-kilo doses and artificial disease models.
Case series and observational studies in humans
No randomized control group; susceptible to selection bias and the placebo effect.
Randomized clinical trials
Control group, randomization and, ideally, double blinding. They are the standard for establishing efficacy.
Systematic reviews and meta-analyses
They integrate several trials; their quality depends on that of the studies included.
The clinical phases
| Phase | Main question | Typical size |
|---|---|---|
| Phase 1 | Is it safe? How does it behave in the body? | Dozens of people |
| Phase 2 | Does it have an effect? At what dose? | Hundreds |
| Phase 3 | Does it work against the standard, in a broad population? | Thousands |
| Phase 4 | What happens after approval, in the long term? | Real-world population |
Surrogate endpoints
A surrogate endpoint is a marker measured instead of the outcome that really matters: IGF-1 instead of body composition, a laboratory value instead of clinical events. They are useful for deciding whether to keep investigating, but improving a marker does not guarantee improving the outcome. The FDA's review of tesamorelin made this explicit: approving it for visceral fat reduction in a specific population does not validate that endpoint for other conditions.
Before assessing a result, ask: in cells, in animals or in people? With a control group? With which endpoint? The answer completely changes the weight of the claim.
Catalogue compounds mentioned in this lesson
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Go to the quiz →Educational content for scientific purposes. It distinguishes preclinical from clinical evidence and is not medical advice, diagnosis or a recommendation for use. NeoPeptidos products are sold labelled for research use only (RUO).