Danazol
Danazol (synthetic attenuated androgen, ethisterone derivative)
Written by Aaron CuhaReviewed Sep 2026
Also known as: Danocrine, Danol, Cyclomen
The one compound here that produced telomere lengthening in humans: 11 of 12 evaluable patients gained telomere length, a mean 386 base pairs at 24 months, in a phase 1 to 2 study stopped early. All 27 patients had inherited telomere disease, telomere length is a biomarker, and nobody measured lifespan.
Overview
Danazol is a synthetic androgen licensed decades ago for endometriosis, fibrocystic breast disease and hereditary angioedema. It reached ageing research through haematology, where androgens have long been used for bone marrow failure, and where somebody noticed that sex hormones regulate expression of the telomerase gene in cell and animal models.
The trial that made its reputation was run at the National Institutes of Health. 27 patients with inherited telomere diseases, conditions in which defective telomere maintenance causes bone marrow failure, liver cirrhosis and pulmonary fibrosis, took 800 mg of danazol a day for a planned 24 months. The primary efficacy endpoint was a 20 percent reduction in the annual rate of telomere attrition at 24 months.
The study was halted early because telomere attrition was reduced in all 12 patients who could be evaluated for the primary endpoint. In the intention-to-treat analysis, 12 of 27, or 44 percent, met the primary endpoint. Unexpectedly, 11 of those 12, or 92 percent, did not merely attrite more slowly but gained telomere length compared with baseline, a mean increase of 386 base pairs. Haematological responses occurred in 19 of 24 evaluable patients at 3 months.
That is a striking result and it is important to be exact about its boundaries. These were patients whose disease is defined by a genetic defect in telomere maintenance. Telomere length was the endpoint. Nobody measured lifespan, healthspan, physical function or mortality, and no healthy person was studied.
Mechanism of action
A synthetic derivative of ethisterone with weak androgenic activity, which suppresses the pituitary gonadal axis and binds androgen, progesterone and glucocorticoid receptors. The telomere rationale is separate from its licensed pharmacology: sex hormones upregulate expression of TERT, the catalytic subunit of telomerase, in tissue culture and animal models, and androgens are aromatised to estrogens which act on an estrogen response element in the TERT promoter. Raising telomerase activity in haematopoietic cells is the proposed route to the observed telomere gain. This is a hormone acting on a gene, not a telomerase drug.
Human evidence
One small single-arm trial in inherited telomere disease that reported telomere elongation, plus long-term follow-up of the same cohort and adverse effect reports from other indications. No trial in healthy people, and no trial with a clinical ageing endpoint.
- 27 patients enrolled, single arm, no placebo group, 800 mg daily, planned 24 months, stopped early at interim because the telomere endpoint was met in all evaluable patients.
- 12 of 27 met the primary endpoint in intention to treat; only 12 patients were evaluable for it at 24 months, which is the number the headline result rests on.
- 11 of 12 evaluable patients gained telomere length rather than merely losing it more slowly, mean increase 386 base pairs, with similar increases seen at 6 and 12 months in exploratory analyses.
- Haematological response, a clinically meaningful outcome in these patients, occurred in 19 of 24 evaluable at 3 months and 10 of 12 at 24 months.
- Adverse effects in the trial: grade 2 or lower liver enzyme elevation in 41 percent and muscle cramps in 33 percent. Outside the trial, reported pancreatitis and, in aplastic anaemia patients, a 30 percent fall in HDL with left ventricular changes at 6 months.
- Nobody has given danazol to healthy people to test an ageing endpoint, and no trial of danazol has measured lifespan, healthspan or mortality.
What this does not tell you: Stopping a single-arm trial early on a biomarker inflates the apparent effect, and everyone involved knows it, which is why the paper reports the intention-to-treat figure of 12 of 27 alongside the 12 of 12 evaluable figure. There was no control group, so the natural history of telomere length in these patients over the same period is not directly observed. Most importantly, these patients have a genetic defect in telomere maintenance and a specific reason to respond to telomerase upregulation. A healthy person's telomere shortening is not the same phenomenon, and there is no evidence that lengthening it in a healthy person would do anything good.
Reading the research record
There are two separate evidence questions about any repurposed drug and they have different answers. The first is whether the drug does what it was licensed to do, which here is settled by randomised trials with hard clinical endpoints. The second is whether it slows ageing in humans, which no trial has tested. The strength of the first answer says nothing about the second. A reader who takes the licensed indication as partial proof of the ageing claim has made the central error of this field.
Danazol is the exception that proves how strict the standard has to be. It produced a real, statistically convincing, biologically surprising human result: telomeres that got longer rather than shorter, in a disease defined by them getting shorter too fast. The result is worth taking seriously and the site's usual line, that no human evidence exists, would be wrong here.
What it is not is evidence that danazol slows ageing. Telomere length is a biomarker, and a contested one. It is measured because it is measurable, it correlates imperfectly with chronological age, and interventions that change it have repeatedly failed to change anything a person would notice. The trial measured telomeres and blood counts over 24 months in 27 people with an inherited disease. It did not measure survival, function or healthspan, and it enrolled nobody without the disease.
There is also a direction-of-risk argument that rarely appears in longevity coverage of this trial. Telomerase upregulation is a mechanism cancers use. In patients whose telomere disease already raises cancer susceptibility the trade was judged worth making under specialist supervision; in a healthy person taking an androgen to lengthen telomeres it is an unmeasured bet in the other direction.
The side effect profile is the rest of the honest picture. Liver enzyme elevation in 41 percent and cramps in 33 percent inside the trial. Outside it, a 2025 study in aplastic anaemia found HDL down 30 percent, LDL up 11 percent and measurable changes in cardiac structure and function after 6 months, and a 2024 Mayo Clinic report describes pancreatitis during danazol therapy for telomere biology disorders. Danazol is an androgen with a boxed warning and it behaves like one.
The evidence, charted
Fig. 1 · evidence composition
5of 5 citations (100%) are in people
Every citation cited here is Human work; no other study type is cited on this page. This count is of our own citation list and understates any literature larger than the sources we cite.
Fig. 2 · evidence over time
Evidence spans 4 distinct years, 2016 to 2026, counted from the citation list on this page.
Fig. 3 · legal status at a glance
US
Approved
UK
Approved
AU
Approved
CA
Approved
Approved in all four jurisdictions shown. A jurisdiction's classification is a regulatory fact, not a verdict on the science; see Legal status below for the full text and any notes.
Fig. 4 · dose response
No human dose response curve exists
We draw this figure where the data supports it. For this compound in humans it does not, so the panel stays empty rather than borrowing an animal curve and implying it transfers.
Key studies & citations
- Human2016
Danazol Treatment for Telomere Diseases
The result that makes danazol interesting. Phase 1 to 2 prospective study, 27 patients with inherited telomere diseases, danazol 800 mg a day orally for a planned 24 months, primary efficacy endpoint a 20 percent reduction in annual telomere attrition. Halted early because attrition was reduced in all 12 patients evaluable for the primary endpoint; 12 of 27 (44 percent) met it in intention to treat. 11 of 12 (92 percent) gained telomere length at 24 months against baseline, mean increase 386 base pairs. Haematological response in 19 of 24 evaluable at 3 months and 10 of 12 at 24 months. Grade 2 or lower elevated liver enzymes in 41 percent and muscle cramps in 33 percent.
New England Journal of Medicine - Human2016
Danazol for Genetic Bone Marrow and Lung Disorders
The registration for the New England Journal of Medicine study. Listed as completed with an actual enrolment of 27, running from July 2011 to November 2016. The registry confirms the single-arm design and the enrolment figure reported in the paper.
ClinicalTrials.gov - Human2026
Danazol treatment for telomere biology disorders: long-term results of a phase 1/2 study
Long-term follow-up of the same National Institutes of Health cohort, published as a brief report ten years after the original. Its existence matters because the original trial was stopped early on a biomarker, and the durability question is the one the early stop left open.
Blood Advances - Human2025
Danazol causes significant changes in the cardiometabolic profile of patients with acquired aplastic anaemia
The cost side, in a different indication. 36 patients with acquired aplastic anaemia on danazol monotherapy at 10 mg per kg per day capped at 600 mg. After 6 months HDL cholesterol fell 30 percent and LDL rose 11 percent, with significant changes in left ventricular mass, ejection fraction and diastolic indices. The authors conclude that danazol causes profound dyslipidaemia and potential cardiac dysfunction.
Blood Cells, Molecules and Diseases - Human2024
Pancreatitis as a Potential Consequence of Danazol Therapy for Telomere Biology Disorders
A Mayo Clinic report describing pancreatitis in the setting of danazol therapy for telomere biology disorders, published eight years after the original trial. An adverse effect identified in ongoing clinical use rather than in the trial.
Mayo Clinic Proceedings
What users report
Self-reported experiences, not evidence. Nothing below was measured under controlled conditions, and reports like these cannot separate a real effect from placebo, from the training or diet change that accompanied it, or from what the product actually contained. They are here because knowing what people describe, including what goes wrong, is worth reading alongside the studies.
- Discussed in longevity circles almost entirely on the strength of the 2016 telomere result, usually without the enrolment numbers, the early stop or the disease context attached.
- Androgenic effects are the dominant complaint where it is used clinically: weight gain, acne, voice change and virilisation in women, some of which does not reverse.
- Liver enzyme monitoring is standard clinical practice on danazol and is frequently absent from self-administered protocols.
Sources: Longevity forums and patient communities in aplastic anaemia and telomere biology disorders. Uncontrolled self-report, and the patient communities are describing a different population from the people considering it for ageing.
Frequently asked questions
Did danazol really lengthen telomeres in humans?
Yes, and that is not a claim this site makes lightly. In the 2016 National Institutes of Health study, 11 of 12 patients evaluable at 24 months gained telomere length compared with baseline, a mean increase of 386 base pairs. All of them had an inherited telomere disease, the trial was single arm with no placebo group, and it was stopped early.
Does that mean it slows ageing?
No. Telomere length is a biomarker, not an outcome. The trial measured telomere length and blood counts over 24 months in 27 people with a genetic telomere maintenance defect. It did not measure lifespan, healthspan, physical function or mortality, and no healthy person has been studied.
Why was the trial stopped early?
Because at the interim analysis telomere attrition was reduced in all 12 patients who could be evaluated for the primary endpoint. Stopping early on a biomarker that is moving in the desired direction tends to overstate the effect size, which is part of why the paper also reports the intention-to-treat figure of 12 of 27, or 44 percent.
What are the side effects?
In the trial, grade 2 or lower liver enzyme elevation in 41 percent and muscle cramps in 33 percent. In wider clinical use, androgenic effects including virilisation in women, and the US boxed warning covers pregnancy, thromboembolism, peliosis hepatis and benign intracranial hypertension. A 2025 study in aplastic anaemia found HDL cholesterol down 30 percent and measurable cardiac changes after 6 months, and pancreatitis has been reported during danazol therapy for telomere disease.
Is it better than telomere supplements?
It is the only thing in this area with a published human telomere elongation result, and that is a real distinction from supplements marketed on cell culture data. It is also a prescription androgen with a boxed warning, studied for two years in 27 people with a rare inherited disease. Those are not the same comparison and neither one supports taking it for ageing.