Zombie cells are real, and pills sold to clear them are still unproven

Key takeaways

• Senescent cells stop dividing but don’t die, and their inflammatory signals can harm nearby tissue; clearing them in mice starting at middle age lengthened average lifespan by about 25%.
• The lead senolytic drug from UNITY Biotechnology, a company co-founded by scientists behind that mouse work, did no better than placebo for knee arthritis pain in 183 patients in 2020.
• In a 2024 Mayo Clinic trial of 60 older women, dasatinib plus quercetin didn’t change the main bone measure, though women with the most senescent cells seemed to benefit.
• Fisetin and quercetin are sold commercially, but the main fisetin trial hadn’t posted results as of October 2026, and quercetin can interact with some medicines.
• Dasatinib, the drug paired with quercetin in these trials, is an FDA-approved leukemia drug, and in 2019 a researcher testing it said people should be warned not to take it for this use yet.

On August 17, 2020, UNITY Biotechnology reported the result it had been building toward. The South San Francisco company had injected a drug into the painful knees of 183 people with osteoarthritis⁴⁶.

The drug, UBX0101, was meant to kill senescent cells, damaged cells nicknamed “zombie cells” because they stop dividing but refuse to die¹⁰. Twelve weeks later, people who got the drug reported about the same pain relief as people who got a placebo shot⁶.

UNITY said it wouldn’t take the drug into larger trials⁶. In 2025, its eye-disease drug also missed its main goal, the company laid off its staff, and by that September its website said it was no longer in operation, according to the advocacy news site Lifespan.io⁷.

The science behind UNITY hasn’t gone away. Drugs that clear senescent cells, called senolytics, are still in human trials¹¹³. Meanwhile, two plant compounds used in those trials, fisetin and quercetin, are sold as commercial products¹⁰.

Mayo Clinic endocrinologist Sundeep Khosla said in 2024 that many people already take them as anti-aging agents without knowing whether they’d benefit¹⁰. This article covers what senescent cells are, what the trials have shown, and why buying a “senolytic” pill today is a bet.

Senescent cells stop dividing, but they don’t go quietly

In the early 1960s, Leonard Hayflick was trying to grow healthy human cells at the Wistar Institute, a research organization at the University of Pennsylvania³. He found that normal human cells could divide only a limited number of times³.

That ceiling became known as the Hayflick limit. Cells that reach it become senescent: alive, but no longer dividing². Hayflick died in August 2024 at 96²³.

Cells also become senescent after other damage, and they pile up with age⁴. That alone might not matter. The trouble is what they release.

Senescent cells pump out a mix of signals that scientists call the SASP, short for senescence-associated secretory phenotype. According to a 2023 review in the journal Cell, the SASP calls in immune cells, drives scarring and can push neighboring cells into senescence too¹.

Picture a worker who has stopped working but won’t leave the office. Worse, this one keeps pulling the fire alarm, and coworkers start to burn out.

Clearing them helped mice live longer and stay healthier

In 2016, a Mayo Clinic team led by Jan van Deursen published a striking result in the journal Nature⁴. Their mice were engineered so that a drug would make senescent cells self-destruct.

Starting at one year of age, roughly middle age for a mouse, the treatment lengthened average lifespan by about 25%⁴⁵. Treated mice had fewer cataracts, better kidney function and hearts that handled stress better⁴. Earlier work in mice bred to age fast had pointed the same way⁵.

The details were less dramatic than the headlines. Maximum lifespan didn’t change much, and treated mice did no better on strength, blood sugar handling or coordination⁵. Judith Campisi of the Buck Institute called it no magic bullet, since the mice still aged and died⁴.

Drugs did similar things. In mice, a combination of dasatinib and quercetin started at 2 years of age, and fisetin started at about 1.6 years, each extended healthy life and lifespan¹.

Note the financial ties. Van Deursen and Campisi co-founded UNITY, which aimed to turn these findings into drugs⁵.

Small human trials hint at benefits, with big caveats

The first human test came in 2019. Fourteen people with idiopathic pulmonary fibrosis, a scarring lung disease, took dasatinib and quercetin three days a week for three weeks⁸⁹.

Their walking speed, six-minute walk distance and chair-stand times improved⁸. Their lung function didn’t change, and the study had no comparison group, so the gains could have other explanations⁸. Respiratory symptoms, bruising or skin irritation, and stomach upset were the most common side effects⁸.

A second early study gave the same drug pair to people with diabetic kidney disease. Afterward, their fat tissue held fewer senescent cells, and some inflammatory signals in the blood fell¹.

The bone trial: a clue about who might benefit

A larger, randomized test came from Mayo Clinic. In a trial reported in Nature Medicine in July 2024, 60 women past menopause were assigned by chance to take dasatinib plus quercetin or nothing¹⁰¹¹¹². Over 20 weeks, they took five monthly courses, each lasting two to three days¹².

The main measure, a blood marker of bone breakdown, didn’t change compared with the untreated group¹¹. A marker of bone building rose about 16% at two and four weeks, then faded by week 20¹¹.

The most interesting finding came from a subgroup. The top third of women by senescent-cell load, measured through a marker in their T cells, drove most of the bone response, including a 2.7% gain in bone density in the radius, a forearm bone¹¹. The authors labeled this an exploratory analysis that needs further study, a lead rather than a conclusion¹¹.

Side effects were common in this open-label trial, where everyone knew which group they were in. Headaches affected 16 of 30 women on the drugs and diarrhea 7 of 30, compared with no headaches or diarrhea among untreated women¹².

Khosla, the senior author, drew a pointed lesson: “Our findings argue against what many people are already doing”¹⁰. Three of the trial’s authors have financial interests, including Mayo patents and pending patents on senolytic drugs, a tie worth knowing¹⁰.

Senescence also protects you, so clearing it all could backfire

Senescence isn’t a design flaw. The 2023 Cell review calls it a powerful defense against cancer, because a damaged cell that stops dividing can’t grow into a tumor¹.

It also helps with repair. After an injury, senescent cells first encourage local scarring, then call in immune cells to clear them¹. Senescence even helps shape the body before birth¹.

A 2020 mouse study showed what can go wrong. A French team led by Dmitry Bulavin removed cells with high levels of a senescence marker called p16¹⁴. Many of those cells lined blood vessels in the liver, where they help filter waste from the blood¹⁴.

The mice fared worse, not better. They developed liver scarring and a platelet problem linked to early death¹⁴. The team concluded that eliminating every senescent cell won’t buy a long, healthy life¹⁴.

That fits the bone trial’s pattern. Senolytics may help people who carry a heavy load of senescent cells and do little for those who don’t, a possibility the Mayo team raised¹⁰.

What’s in a “senolytic” supplement bottle

Quercetin is a flavonoid, a type of plant compound, and the one people eat most. It’s found in onions, apples, black and green tea, citrus, red grapes, cherries and raspberries¹⁵. Fisetin is another plant compound.

Both are sold as commercial products¹⁰. Our article “The FDA reversed itself on NMN while the human evidence stayed thin” covers other longevity supplements, and “No Supplement Is FDA Approved. How to Tell a Real Seal From Decoration” explains what a supplement label does and doesn’t promise.

Trial doses aren’t supplement doses

The trials gave large, brief doses on a schedule. The bone trial’s fisetin group took about 20 mg per kilogram of body weight a day for three days in a row, once a month¹². For a 154-pound (70 kg) woman, that’s about 1,400 mg a day, or 14 of the trial’s 100 mg capsules, by our math.

Quercetin went with dasatinib at 1,000 to 1,250 mg a day for a few days at a time⁸¹². In the trials described here, quercetin was always paired with dasatinib.

What fisetin has shown in people so far

The Mayo bone trial had a small fisetin group of 14 women¹². They showed no gain in bone density after 20 weeks, and their bone-building marker fell at two weeks¹². Two withdrew because of side effects, and one had a serious stomach bleed. The registry record doesn’t say whether fisetin caused it¹².

A group that small can’t settle much. The main test is AFFIRM-LITE, a placebo-controlled Mayo trial of fisetin for frailty and inflammation in older adults. It began in November 2018, and as of October 2026 its results hadn’t been posted¹³.

Safety and interactions

Memorial Sloan Kettering Cancer Center’s herb database says no study has shown that quercetin treats cancer or any other disease¹⁵. In lab studies, it blocks liver enzymes known as CYP3A4 and CYP2C19, which break down many medicines, though how much that matters in people is unknown¹⁵.

The database also describes a 79-year-old man on the blood thinner warfarin whose clotting test rose too high while he took quercetin. It returned to normal after he stopped¹⁵.

Dasatinib is a different matter entirely. It’s an FDA-approved leukemia drug⁹¹⁰. In 2019, James Kirkland, one of the study researchers, said people calling to ask for these drugs should be warned not to take them yet, because no one knew their side effects when given this way⁹. The trials, he said, enrolled patients with very serious, life-threatening illness, where that risk was acceptable⁹.

The senolytic claim check

This table is our own tool. Match a claim you’ve seen to a row.

Claim	What was tested	In whom	Result	Rating
“Clearing zombie cells extends life”	Genetic removal of senescent cells from age 1	Mice	About 25% longer average life; maximum lifespan little changed45	Promising but early (mice only)
“Senolytics lower senescent cells in people”	A short course of dasatinib plus quercetin	Adults with diabetic kidney disease	Fewer senescent cells in fat; fewer inflammatory signals1	Promising but early
“Senolytics restore physical function”	Nine doses over three weeks	14 adults with lung scarring, no comparison group	Better walking and chair-stand times; no change in lung function8	Promising but early
“Senolytics ease arthritis pain”	One knee injection of UBX0101	183 adults with knee arthritis	No better than placebo at 12 weeks6	Evidence says no for that drug
“Senolytics build bone”	Five monthly courses of dasatinib plus quercetin	60 women past menopause	Main marker unchanged; brief rise in bone building; possible benefit in those with most senescent cells11	Promising but early
“Fisetin clears zombie cells”	High doses three days a month	14 women in a bone trial; main trial unreported1213	No bone benefit in the small group	Not enough evidence
“Quercetin alone is a senolytic”	Always paired with dasatinib in these trials812	None alone	No separate result	Not enough evidence
“Clearing all senescent cells is safe”	Removing high-p16 cells	Mice	Liver scarring and early death14	Evidence says no, or unsafe (in mice)
“Exercise clears zombie cells”	Not tested in any trial described here	None	No result	Not enough evidence

Natural-health values and the senolytic shelf

The senescence story should appeal to anyone who trusts the body’s own systems. Senescence is one of them: a built-in brake on cancer and a helper in healing¹. The lesson from the mouse studies is balance, not a war on a natural process¹⁴.

Food comes first here too. Onions, apples, tea and berries carry quercetin¹⁵, with a long record as everyday foods. A high-dose capsule taken on a trial schedule is a different thing.

Apply skepticism in every direction. Patents on senolytic drugs¹⁰ and a startup’s investors⁵ give researchers reasons to talk up results. Supplement sellers have the same incentive. Ask everyone for the human trial.

Researchers also call drugs that might quiet the SASP without killing cells “senomorphics”¹. Whether habits work that way in people hasn’t been tested in the trials covered here. Exercise has well-documented benefits of its own, as “Activity tracks with lower risk of 13 cancers, and even one-minute bursts count” explains.

Questions readers ask

The bottom line

Senescent cells are real, they build up with age, and clearing them helped old mice stay healthier. In people, small trials of a cancer drug paired with quercetin show early signals, mainly in those carrying the most senescent cells, while the first company built on the idea failed in arthritis and closed.

Fisetin and quercetin supplements haven’t been shown to clear senescent cells or improve health when taken on their own. Until the trials report, a “senolytic” capsule is a bet. Put your money first on what has proof, and talk with your clinician before trying anything that may interact with your medicines.

Related reading

• Your cells age in 12 known ways, and most fixes have only worked in mice
• CDC tied HIV infections to spa facials, so score risky treatments before you pay
• How to sort longevity clinics that mix proven care with pricey experiments
• What happens when you don’t tell your doctor about supplements
• No Supplement Is FDA Approved. How to Tell a Real Seal From Decoration

Sources

1. López-Otín C, Blasco MA, Partridge L, Serrano M, Kroemer G. “Hallmarks of aging: An expanding universe.” Cell, 2023;186:243 (author manuscript via Spain’s Instituto de Salud Carlos III repository). repisalud.isciii.es
2. Elliott B. “In Memory of Leonard Hayflick.” British Society for Research on Ageing, August 5, 2024. bsra.org.uk
3. Risen C. “Leonard Hayflick, Who Discovered Why No One Lives Forever, Dies at 96.” The New York Times, August 2024 (reposted by HealthSpan Action Coalition). healthspanaction.org
4. Greenfieldboyce N. “Boosting Life Span By Clearing Out Cellular Clutter.” NPR, republished by WGBH, February 3, 2016. wgbh.org
5. Regalado A. “In New Anti-Aging Strategy, Clearing Out Old Cells Increases Life Span of Mice by 25 Percent.” MIT Technology Review, February 3, 2016. technologyreview.com
6. UNITY Biotechnology. Press release on the Phase 2 study of UBX0101 in knee osteoarthritis, Form 8-K Exhibit 99.1, U.S. Securities and Exchange Commission, August 17, 2020 (company source). sec.gov
7. Lifespan.io. “Unity Biotechnology” (organization profile, longevity advocacy news site), accessed October 2026. lifespan.io
8. Justice JN, et al. “Senolytics in idiopathic pulmonary fibrosis: Results from a first-in-human, open-label, pilot study.” EBioMedicine, 2019;40:554–563. pubmed.ncbi.nlm.nih.gov
9. Lutz R. “Senescent Cell Research Shows Potential for Idiopathic Pulmonary Fibrosis.” HCPLive, January 14, 2019. hcplive.com
10. Madson R. “Drugs that kill ‘zombie cells’ may benefit some older women, but not all, Mayo Clinic study finds.” Mayo Clinic News Network, July 2, 2024. newsnetwork.mayoclinic.org
11. Farr JN, et al. “Effects of intermittent senolytic therapy on bone metabolism in postmenopausal women: a phase 2 randomized controlled trial.” Nature Medicine, 2024;30(9):2605–2612 (PubMed abstract). pubmed.ncbi.nlm.nih.gov
12. ClinicalTrials.gov. “Targeting Cellular Senescence With Senolytics to Improve Skeletal Health in Older Humans” (NCT04313634), Mayo Clinic, results posted July 22, 2024. classic.clinicaltrials.gov
13. FDAAA TrialsTracker. “NCT03675724: AFFIRM-LITE, Alleviation by Fisetin of Frailty, Inflammation, and Related Measures in Older Adults,” Mayo Clinic, checked October 21, 2026. fdaaa.trialstracker.net
14. Inserm. “Eliminating senescent cells is not the answer to a long and healthy life” (on Grosse L, et al., Cell Metabolism, 2020). Press release, June 8, 2020. presse.inserm.fr
15. Memorial Sloan Kettering Cancer Center. “Quercetin.” About Herbs database, updated October 10, 2023. mskcc.org