Rapamycin, metformin and the race to slow aging

If you follow longevity research, two names come up constantly: rapamycin and metformin. Neither was designed to slow aging. Both became the drugs every new idea is compared against.

That status is earned. Both are approved drugs with long clinical histories, both act on pathways that are clearly linked to aging, and both have produced results in animal studies that the field takes seriously. When researchers claim a new compound slows aging, the first question is usually how it compares with these two.

Rapamycin

Rapamycin was discovered in soil from Easter Island, Rapa Nui, which gave it its name. It is used to prevent organ transplant rejection. It acts on mTOR, a central switch that tells cells whether to grow or conserve resources. In 2009, a large US program found that rapamycin extended lifespan in mice, even when treatment started late in life. That result changed the field.

The late-life part is what made it so important. Many interventions that extend lifespan in animals only work if they start early. A drug that still helps when given to older animals is far more relevant to people, because nobody begins an anti-aging treatment at birth. It also strengthened the case that mTOR is not just a growth regulator but a genuine control point for aging.

Metformin

Metformin is one of the most prescribed diabetes drugs in the world. Observational studies hinted that people taking it might live longer, which led researchers to propose dedicated trials to test whether it slows aging itself.

What extends life in a mouse does not automatically extend healthy life in a person.

Its appeal is partly practical. Metformin is inexpensive, widely available and has been used by very large numbers of people for decades, so its safety profile is well understood. But observational data have limits. People who take a given drug may differ from those who do not in many ways, and only a controlled trial can separate the effect of the drug from everything else.

Why caution matters

Both drugs have real side effects, and what extends life in a mouse does not automatically extend healthy life in a person. That is why, in our yeast screen, beating rapamycin and metformin was a meaningful benchmark, not a promise.

Rapamycin suppresses parts of the immune system, which is exactly why it works in transplant patients and exactly why it needs care in healthy people. Metformin also has side effects, and its benefits in people without diabetes are still being tested. Taking either drug on your own to slow aging is not something the evidence currently supports.

My perspective

I think these two drugs are best understood as proof of principle. They show that aging can be pharmacologically modified in animals, and they give researchers a clear yardstick. The goal now is to find interventions that keep the benefit and lose the cost, and to measure success in years of healthy life, not just years.

mTOR, by the way, came back years later in my cancer work. In biology, the same switches keep showing up.