Quick answer

In people, the changes measured in trials took weeks: a blend trial found nothing after 1 week but higher oxygen uptake after 3, and immune cell changes showed at 4 to 8 weeks. The ant fungus is a different species; in a lab study, ants that took up its biting position died 16 to 24 days after injection.^1,2,3,4

Key facts

By the end of a 4-week trial, natural killer cell activity was higher with 1.5 g a day of Cordyceps militaris than with placebo.²
Five weeks of 3 g a day did nothing measurable for trained cyclists.⁵
The exercise trial in older adults ran for 12 weeks.⁶
Cordyceps militaris trials reviewed in 2026 lasted from 1 to 16 weeks.⁷

What changed, and when

Set out by time point, the trials show a pattern: little or nothing at one week, and the clearer changes after three weeks or more of daily use. Even then, several trials found no change at all.^1,5

Cordyceps results by time point^{1,2,5,6,8,9,10}
When checked	Amount and group	Result
3 and 24 hours after one 1 g dose	Young adults after hard cycling	Muscle cells responded differently than with placebo
1 week	About 4 g a day of a blend, young adults	No difference from placebo
2 weeks	3 g a day, trained runners	Longer time to exhaustion and higher oxygen uptake than placebo, reported in a 2025 review
3 weeks	About 4 g a day of a blend, 10 young adults	Higher maximal oxygen uptake than placebo
4 weeks	1.5 g a day, healthy men	Natural killer cell activity above placebo
5 weeks	3 g a day, trained male cyclists	No change
8 weeks	1.68 g a day of a mycelium extract, adults	Natural killer cell activity up by about 39% against placebo
12 weeks	About 1 g a day, adults aged 50 to 75	Higher metabolic and ventilatory thresholds, the same peak oxygen uptake
12 weeks	2 g a day, amateur marathon runners	Faster 5 km times, reported in a 2025 review

The graded claims and their timescales

May support aerobic exercise capacity at 1 to 4 g a day taken for several weeks; results disagree, including in trained athletes*^1,5,6,7,9

Early evidence

In 20 adults aged 50 to 75, a cultured cordyceps mycelium (Cs-4) at 333 mg three times a day for 12 weeks raised two exercise thresholds by 8.5% and 10.5%, with no change in maximal oxygen uptake. In 28 young adults, 4 g a day of a mushroom blend containing Cordyceps militaris made no difference after 1 week; in the 10 who continued for 3 weeks, maximal oxygen uptake rose compared with placebo. In 22 trained male cyclists, 3 g a day for 5 weeks changed nothing measured. A 2025 meta-analysis of two or three small trials found borderline gains, and a 2026 review called the Cordyceps militaris trials inconsistent.

Amount studied: About 1 to 4 g a day for 3 to 12 weeks

In a Cordyceps militaris blend trial, maximal oxygen uptake did not differ from placebo after 1 week but did after 3 weeks.¹

May raise natural killer cell activity, one measure of immune function, in healthy adults; whether this means fewer illnesses was not tested*^2,3,10

Early evidence

In 79 healthy Korean men, 1.5 g a day of Cordyceps militaris for 4 weeks raised natural killer cell activity and lymphocyte growth more than placebo. In 79 healthy adults, 1.68 g a day of a cordyceps mycelium extract (Paecilomyces hepiali) for 8 weeks raised natural killer cell activity by about 39% compared with placebo. In a 40-person trial of a Cordyceps militaris drink, activity rose in men by 4 weeks against their starting level and, compared with placebo, in women by 8 weeks. The trials were small and short, and none counted illnesses.

Amount studied: 1.5 to 1.7 g a day for 4 to 8 weeks

Natural killer cell activity was measured at 2 and 4 weeks in one trial and at 4 and 8 weeks in another. In the drink trial, the change showed in men at 4 weeks and in women at 8 weeks.^2,3

Both kinds of change were measured after weeks of daily use. We found no trial that checked people again after they stopped, so how long any effect lasts is unknown.^1,2,3

In ants: the zombie fungus

In a laboratory experiment with carpenter ants injected with the ant fungus, the ants found in the typical biting position were those that died 16 to 24 days later.⁴

That is where searches about cordyceps and ants come from. The ant fungus, Ophiocordyceps unilateralis, is not the species sold as a supplement, and each of its species attacks particular kinds of ant. Inside the ant it fills the jaw muscles that clamp onto a leaf, not the brain.^11,12

Supplement cordyceps is grown in laboratories or farmed rather than collected from insects.^1,13

How long people have taken it

The longest trials ran 12 to 16 weeks, and a safety study gave a related species every day for 3 months without changes in liver or kidney blood tests. The one serious liver case on record came after 5 years of a daily cordyceps tablet.^6,7,14,15

Ask your doctor before taking it for months if you take daily medicines, especially a blood thinner, insulin or a medicine that suppresses the immune system^2,16,17
Ask first if you have liver disease¹⁵
Ask first if you are pregnant, breastfeeding or under 18

Questions people ask

How long does it take for cordyceps to kick in?

In the exercise trials, nothing changed after 1 week, and the clearer results came after 3 to 12 weeks of daily use. Immune cell changes were measured at 4 to 8 weeks.^1,2,6,10

How long does cordyceps take to work in ants?

In a laboratory experiment, the carpenter ants that ended up in the biting position had died 16 to 24 days after the ant fungus was injected. That fungus is a different species from supplement cordyceps.^4,11

Can you take cordyceps every day?

Trials gave it every day for up to 12 to 16 weeks with few side effects, and LiverTox rates it an unlikely cause of liver injury. For longer use, or if you take daily medicines, ask your doctor first.^6,7,13

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Sources

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.