What is a randomized controlled trial?
RCT
A randomized controlled trial is a study where people are assigned by chance, like a coin flip, to get either the treatment or a comparison such as a placebo, so any difference can be credited to the treatment.
Imagine testing a new fertilizer by planting two identical gardens, then flipping a coin to decide which one gets it. If that garden grows better, you can be fairly sure it was the fertilizer, not the soil or the sunlight.
Why it matters for aging
The coin flip is the key ingredient. If people chose their own group, healthier or more motivated people might pick the treatment, and you couldn't tell whether the treatment or the people made the difference. Random assignment spreads those differences evenly.
The best trials are also "double-blind": neither participants nor researchers know who got what, which stops expectations from coloring the results. When reading one, check the main result the trial was designed to test, its size, its length and who funded it.
A common myth
Any study that shows a benefit proves the treatment works.
Observational studies, which simply watch what people do, can't separate cause from coincidence. Randomized trials can, which is why we grade them "A". Even so, a small or short trial can still miss things or find flukes.
Go deeper
Deep dives
- Does urolithin A work? What the human trials actually show
- CoQ10: who actually needs it?
- Does intermittent fasting slow aging? What the trials say
Related terms
Updated Nov 9, 2026 · All terms