Rapamycin is one of the most promising longevity drugs—a molecule that could help humans live longer, healthier lives.

Most medical treatments target one disease at a time but, if we could safely slow aging, we might delay or prevent many of these illnesses together. In the lab, dozens of experiments have shown that rapamycin can make mice live up to 30% longer, and there is some evidence that there could be similar effects in marmosets and even humans.

Many scientists would bet that rapamycin will be the first longevity drug with demonstrable human benefits. So, where did it come from, and what do we know about this molecule?

The tall tale of a drug from Easter Island

Rapamycin was originally discovered in a soil sample collected on Easter Island, famous for its huge Moai stone heads. The drug is named after the island, which is known as Rapa Nui in the local Polynesian language.

After being isolated from bacteria in the island soil, rapamycin was developed into a successful drug. It is currently used in people to help transplant patients avoid organ rejection, as a cancer treatment, and as a coating on stents placed in arteries to keep them open.

The modern story of rapamycin as a potential longevity intervention really took off in 2009. That year, researchers at the Interventions Testing Program (ITP) published a landmark study showing that rapamycin extended the lifespan of laboratory mice—even when the drug was started late in life, equivalent to around 60 years old in human terms.

Since 2009, dozens of independent studies across various laboratories have confirmed that rapamycin can extend lifespan in mice, sometimes by as much as 20–30%, depending on the dose. Importantly, rapamycin doesn’t just make mice live longer—it also improves ‘healthspan’, the period of life spent free from disease. Mice treated with rapamycin tend to have healthier immune systems, better heart function, and delayed onset of cancers compared with untreated controls.

How rapamycin works: the mTOR pathway

Rapamycin works by inhibiting a protein complex inside cells called mTOR (mechanistic Target Of Rapamycin—if that sounds circular, it’s because the protein complex was discovered using rapamycin!).

When nutrients and energy are abundant, mTOR is active, and drives cells to grow and divide. When nutrients are scarce, mTOR is dialled down, which activates a cellular spring-cleaning process called ‘autophagy’—literally ‘self-eating’—which removes broken cellular components and recycles their chemical constituents.

By dialing down mTOR activity, rapamycin appears to shift cells from ‘growth mode’ into ‘maintenance mode’, which may help repair ageing damage and improve resistance to stress.

This mechanism fits with decades of work showing that dietary restriction—cutting back calories or protein which has been known for decades to extend lifespan in animals—also reduces mTOR signaling.

Beyond mice: evidence in other animals

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While mouse studies are valuable, they don’t always predict what will happen in humans. That’s why researchers have tested rapamycin in a growing range of other animals.

• Worms, flies, and yeast: Rapamycin extends lifespan in short-lived species like C. elegans and Drosophila. These findings suggest that the drug acts on a fundamental biological pathway conserved across evolution.
• Dogs: Early studies in companion dogs suggest that short courses of rapamycin may improve heart function and overall health, and large-scale trials are now underway in pet dogs across the U.S.
• Non-human primates: In 2023, a study in common marmosets—small monkeys with relatively short lifespans—reported that long-term rapamycin treatment was safe and well tolerated, with beneficial effects on metabolic and immune markers. This was the first controlled trial in a primate species, bringing the evidence base one step closer to humans.

Taken together, these studies build a compelling case that rapamycin’s effects on aging are not limited to laboratory mice, but may be relevant across mammals.

Human data: medical use and clinical trials

Unlike many experimental longevity compounds, rapamycin has already been used in humans for more than 20 years, meaning we already have some idea of its safety and side-effects.

One important point is that transplant patients typically receive high daily doses of rapamycin or related drugs, along with other immunosuppressants. At those levels, side effects like mouth ulcers, delayed wound healing, and increased infection risk can occur. But these may not reflect what happens at lower, intermittent doses, which are being tested for aging-related indications.

There have also been studies of using similar drugs to improve immunity in old age. Trials of related drugs everolimus and RTB101 in older adults demonstrated improved response to a flu vaccine, suggesting rejuvenation of immune function. The trials also reported that treatment was generally safe and well tolerated, and severe side effects were rare.

There is also informal research which is suggestive of rapamycin’s benefits. A survey of biohackers

Safety, unknowns and the future

So should everyone start taking rapamycin to stay young? The answer is not yet. Despite the promising evidence, several uncertainties remain:

• Optimal dosing: We don’t yet know the best schedule (daily vs. weekly, short-term vs. continuous) or the ideal dose for healthspan benefits without undue risk.
• Long-term safety: While short-term trials look encouraging, we lack large, long-duration studies in generally healthy older adults.
• Side effect profile: Even at lower doses, rapamycin can cause mouth ulcers, lipid changes, or impaired wound healing in some people. The balance of benefits versus risks is still being clarified.
• Regulatory status: Rapamycin is approved for certain medical conditions but not for aging. Using it as a longevity drug would currently be considered “off-label.”

The only way to address these uncertainties is a proper clinical trial of rapamycin in older adults, to see if it really can stave off the ravages of time—something that we at The Longevity Initiative will be campaigning for, and investigating funding and policy to enable.