“Cordyceps” draws around a hundred thousand searches a month on Yandex, sits on pharmacy and marketplace shelves, and every third product description carries the words “endurance”, “oxygen” and “ATP”. The legend is older than most of the buyers: in 1993 the Chinese women runners of Ma Junren's group set a string of world records, and the coach credited “turtle soup and cordyceps”. In 2016 it emerged that the records were set on doping. The legend was none the worse for it.

How much of it is down to the fungus? Cordyceps has rarely been tested in humans, and in 2026 one more study came out. Here are all four placebo-controlled studies together.

What it actually is

Ophiocordyceps sinensis is a fungus that parasitises caterpillars in the highlands of Tibet and Nepal. The wild form costs more than gold by weight, so there is practically none of it in supplements. What is in them is either Cs-4 — fermented mycelium grown in culture — or Cordyceps militaris, a related species grown on substrate. The active compounds are said to be cordycepin and adenosine; the claimed mechanism is “improved oxygen utilisation” and “increased ATP”. A beautiful mechanism, but it has never been demonstrated in human muscle.

The 2026 RCT: a single dose before a test to exhaustion

Farzan and Koushkie Jahromi (PLoS One, July 2026) took 12 young men, active but untrained — mean VO₂max 38.6 ml/kg/min. A double-blind crossover design with a one-week washout: 1 g of standardised C. militaris extract or corn starch 30 minutes before a maximal cycle test to exhaustion. Before and 3 minutes after: a Stroop test (reaction time and accuracy), oxygen uptake, glucose, blood pressure, heart rate.

The results:

Post-exercise reaction time was faster on cordyceps: 964 ± 85 versus 1,034 ± 84 ms (p = 0.042, d = 0.88). Before exercise there was no difference. The condition × time interaction was non-significant (p = 0.337): in other words, cordyceps did not change the response to exercise, it simply produced slightly faster answers overall.
Accuracy in both conditions was above 99% — the ceiling of the test.
Resting oxygen uptake was higher: 0.37 versus 0.24 L/min (p = 0.022). Peak VO₂ — no difference (p = 0.49).
Glucose, blood pressure, heart rate — no effects.

The authors put it honestly: an acute cognitive effect, unrelated to exercise. Note that “resting VO₂ +54%”: if it were real, a person at rest would be burning one and a half times more oxygen — that is not “improved utilisation”, it is either measurement noise in 12 people or a mild thermogenic effect. No endurance benefit follows from it, and the peak values confirm that.

The three studies before it

Trained cyclists, 5 weeks — nothing. Parcell and colleagues (IJSNEM, 2004): 22 male cyclists, Cs-4 at 3 g/day for 5 weeks, training supervised. VO₂peak: 59.9 → 60.1 on placebo and 59.1 → 57.1 on cordyceps. Ventilatory threshold unchanged. Time trial: 61.4 min on placebo versus 62.1 on cordyceps. This is the only study with trained endurance athletes and a real performance test — and it is negative.

Cyclists, cordyceps + rhodiola, 2 weeks — nothing. Earnest and colleagues (MSSE, 2004): 17 category III/IV racers, a commercial blend of 1,000 mg of Cs-4 and 300 mg of rhodiola extract plus pyruvate, phosphates and ribose. Peak VO₂, time to exhaustion, peak power, power at 2 and 4 mmol/L of lactate — no differences.

Pensioners, 12 weeks — the thresholds shifted. Chen and colleagues (JACM, 2010): 20 healthy people aged 50–75, Cs-4 at 333 mg three times a day. The metabolic threshold rose by 10.5% (0.83 → 0.93 L/min), the ventilatory threshold by 8.5%; VO₂max — unchanged in both groups. A pilot on 20 untrained people; it does not transfer to young athletes.

A mushroom blend, 3 weeks — a rise in VO₂max in ten volunteers. Hirsch and colleagues (Journal of Dietary Supplements, 2017): 28 people, 4 g/day of a mushroom blend containing C. militaris (not pure cordyceps). After one week — nothing: p from 0.13 to 0.82 across all measures. After three weeks, in the ten who continued — VO₂max +4.8 ml/kg/min (p = 0.042) and time to exhaustion +69.8 s by confidence-interval analysis. Ten people, a commercial blend, an effect that appears only after two-thirds of the sample has vanished — that is a hypothesis, not a result.

Adding it up

The only study in which cordyceps was given to trained endurance athletes and a race result was measured is negative. The only one with a clear VO₂max gain was in ten untrained people, on a mushroom blend. The fresh 2026 RCT is about reaction time, not endurance. Not one study has shown that cordyceps makes someone who already trains any faster.

What to do

For endurance — do not spend the money. The evidence base in athletes is two negative studies from 2004 and nothing since.
If you try it anyway — compare a test, not feelings: the same distance, the same conditions, before and after four weeks. The expected effect according to the literature is zero, and zero is easy to “see” through suggestion.
Look at the composition. “Cordyceps” on the label is almost always Cs-4 or militaris at 0.5–3 g; wild O. sinensis in a 500-rouble jar of capsules is absent by definition. In 2016 the Chinese regulator warned of arsenic in products made from wild cordyceps — one more argument not to chase the “real thing”.
Drug interactions are real: potentiation of anticoagulants and immunosuppressants has been described. If you take either, discuss it with your doctor.
The cognitive effect is the only thing with any support at all: 70 ms on a Stroop test in 12 people. For sport it means nothing; for marketing it is a new headline.

The bottom line

The 2026 RCT: 12 men, 1 g of extract, post-exercise reaction time 70 ms faster, peak VO₂ unchanged.
Trained cyclists, 3 g/day, 5 weeks: VO₂peak 59.1 → 57.1, time trial 62.1 versus 61.4 min on placebo — no effect.
A blend with rhodiola, 2 weeks in racers — no effect.
Gains in thresholds only in 20 pensioners, and in VO₂max only in 10 untrained people on a mushroom blend.
In athletes not one study has shown a performance gain; “natural EPO” is a 1993 legend, explained by doping in 2016.

Sources: Farzan H., Koushkie Jahromi M. “Acute Cordyceps militaris supplementation and elevated resting oxygen uptake with faster reaction times: A randomized crossover trial”. PLoS One, 2026;21(7):e0351725. DOI: 10.1371/journal.pone.0351725 · Parcell A.C., Smith J.M., Schulthies S.S., Myrer J.W., Fellingham G. “Cordyceps Sinensis (CordyMax Cs-4) supplementation does not improve endurance exercise performance”. International Journal of Sport Nutrition and Exercise Metabolism, 2004;14(2):236–242. DOI: 10.1123/ijsnem.14.2.236 · Earnest C.P. et al. “Effects of a Commercial Herbal-Based Formula on Exercise Performance in Cyclists”. Medicine & Science in Sports & Exercise, 2004;36(3):504–509. DOI: 10.1249/01.MSS.0000125157.49280.AF · Chen S., Li Z., Krochmal R., Abrazado M., Kim W., Cooper C.B. “Effect of Cs-4 (Cordyceps sinensis) on exercise performance in healthy older subjects: a double-blind, placebo-controlled trial”. Journal of Alternative and Complementary Medicine, 2010;16(5):585–590. DOI: 10.1089/acm.2009.0226 · Hirsch K.R., Smith-Ryan A.E., Roelofs E.J., Trexler E.T., Mock M.G. “Cordyceps militaris Improves Tolerance to High-Intensity Exercise After Acute and Chronic Supplementation”. Journal of Dietary Supplements, 2017;14(1):42–53. DOI: 10.1080/19390211.2016.1203386