Mifepristone

The reason anyone tested this is worth stating, because it is a good hypothesis. Cortisol rises with age, and sustained glucocorticoid exposure causes exactly the changes that define ageing badly: muscle wasting, bone loss, visceral fat accumulation, insulin resistance, hippocampal atrophy and immune suppression. Block the receptor and those should slow.

Mifepristone is the available tool, a potent antagonist at both the glucocorticoid and progesterone receptors, already approved for Cushing's syndrome hyperglycaemia and, separately and controversially, for pregnancy termination.

In the Interventions Testing Program's 2026 cohort it did not increase lifespan in male or female mice. That is the answer the hypothesis got when it was tested properly.

This compound was one of eleven in the Interventions Testing Program cohort reported in 2026, and none of the eleven significantly increased lifespan in either sex. The cohort is worth understanding as a whole. It deliberately retested astaxanthin, mitoglitazone and meclizine, three compounds the same programme had previously found to extend lifespan, at different doses or starting at later ages. All three showed no benefit the second time. In females, pooling all three sites, astaxanthin, late-start mitoglitazone and pioglitazone were associated with significantly reduced lifespan; site-specific reanalysis found unusually long-lived control females at one site, and excluding it left the negative effect for mitoglitazone and pioglitazone only. The authors' own conclusion is that timing and dosage are critical variables and that single-site or single-cohort findings need cautious interpretation.

The useful thing this null does is constrain a popular story. That chronic stress and cortisol drive ageing is repeated constantly, and the mechanistic case for it is genuinely strong. Blocking the receptor for a lifetime in mice should have been the clean test, and it produced nothing. That does not disprove the cortisol story, because a blunt lifelong blockade of a hormone with essential functions is not the same intervention as reducing excess exposure. It does mean the obvious pharmacological version of the idea has been tried and has failed.

The Interventions Testing Program is run by the National Institute on Aging at three independent sites, The Jackson Laboratory, the University of Michigan and the University of Texas Health Science Center at San Antonio. It uses UM-HET3 mice, a genetically heterogeneous four-way cross, so a result cannot be an artefact of one inbred strain. Compounds are fed in the diet, both sexes are tested, cohorts are large enough to detect roughly a 10 percent lifespan change, and results are analysed by log-rank for median survival and by the Wang-Allison test for maximum lifespan. Its nulls are published alongside its positives. That combination of features does not exist anywhere else in ageing research, which is why a null here means considerably more than a null from a single laboratory.