Randomized controlled trial (RCT)

A randomized controlled trial (RCT) is an experimental study design in which participants are allocated to an intervention or control condition through a chance-based process — the most reliable method for establishing whether a treatment causes its observed effect. Randomization distributes known and unknown confounders evenly across groups so that outcome differences are attributable to the intervention rather than pre-existing group differences. Blinding — masking participants, clinicians, or assessors to group assignment — reduces bias; double-blind designs, where neither party knows the allocation, are the strongest configuration. In longevity research, RCTs separate causal claims from association: several interventions appearing protective in cohort studies showed smaller or no benefits when rigorously tested. RCTs in aging science are difficult because meaningful endpoints such as delayed multimorbidity or extended lifespan require decades of follow-up. The TAME trial (Targeting Aging with Metformin), enrolling ~3,000 adults aged 65–79 with a composite age-related disease endpoint, shows the field's effort to test a geroscience intervention at scale. As of 2026, no anti-aging intervention has completed a powered RCT with all-cause mortality as a primary endpoint in humans.