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Limited evidenceLongevity & antioxidants

Ergothioneine

An unusual amino acid with a dedicated human transporter and a plausible case for being a conditionally essential nutrient — but the clinical evidence is one small pilot trial. Interesting biology, almost no outcome data.

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What the science says

  • Absorption and tissue accumulation Moderate evidence

    Humans have a specific transporter (OCTN1/SLC22A4) that concentrates ergothioneine in erythrocytes, liver, kidney, eye and brain, and it is retained with a half-life of roughly 30 days. A controlled pharmacokinetic study in healthy adults (Cheah et al., 5-25 mg/day for 7 days) confirmed dose-dependent uptake with minimal excretion — the body clearly wants to keep it. The existence of a dedicated transporter is the strongest argument for its being physiologically important.

  • Cognitive decline Limited evidence

    A 2024 pilot randomized study in subjects with mild cognitive impairment reported some improvement on cognitive measures with ergothioneine, but it was explicitly a pilot — small, short and underpowered for a definitive answer. It should be read as a signal justifying a larger trial, not as evidence of efficacy.

  • Low blood levels and disease risk Limited evidence

    Observational work consistently finds lower plasma ergothioneine in people with mild cognitive impairment, frailty, cardiovascular disease and higher all-cause mortality. But ergothioneine comes almost entirely from mushrooms, oats, beans and organ meats, so low levels track diet quality, and no causal inference is possible from these data.

  • Oxidative damage and inflammation biomarkers Limited evidence

    In the Cheah healthy-volunteer study, ergothioneine supplementation did not produce significant changes in markers of oxidative damage or inflammation in healthy people — which the authors reasonably attributed to a lack of baseline oxidative stress to improve. Either way, no biomarker benefit was demonstrated in healthy adults.

Dosage & safety

Studied doseStudied at 5-30 mg/day; the pharmacokinetic work used 5-25 mg/day and cognitive pilot work used around 5-25 mg/day. Typical dietary intake is roughly 1-5 mg/day in Western diets, with king oyster, oyster and shiitake mushrooms by far the richest sources — a large serving of oyster mushrooms can supply several milligrams. Because retention is so long, daily dosing is not strictly necessary to maintain levels. No dose has been tied to a clinical outcome.
SafetyVery well tolerated in the human studies conducted to date, with no significant adverse effects at up to 25-30 mg/day and no toxicity signals in animal studies even at high doses; it has US FDA GRAS status and EFSA novel food authorization (up to 30 mg/day for adults, with lower limits for children and a maximum of 20 mg/day in pregnancy and lactation per the EFSA opinion). Human safety data beyond a few weeks are limited. Because it accumulates via OCTN1 and OCTN1 polymorphisms are associated with Crohn's disease and rheumatoid arthritis, the biology in inflammatory disease is not fully understood. Supplements are expensive relative to simply eating mushrooms regularly.

How to take it

TimingTiming does not matter, and because it is retained in tissue for weeks, a missed day is unimportant.
With food?With or without food.
Worth knowingA large serving of oyster, king oyster or shiitake mushrooms supplies several milligrams for a fraction of the price of a capsule.

Frequently asked questions

What is ergothioneine and why do people take it?

Ergothioneine is an amino acid that humans concentrate through a dedicated transporter and retain for weeks, suggesting it may be conditionally essential. The clinical evidence for ergothioneine is limited to one small pilot trial.

Does ergothioneine help memory or cognitive decline?

The evidence is limited: a 2024 pilot study in mild cognitive impairment reported some improvement with ergothioneine, but it was small, short and underpowered. Low ergothioneine levels in cognitive decline are observational and likely track diet quality.

How much ergothioneine per day?

Ergothioneine has been studied at 5-30 mg/day, and EFSA authorises up to 30 mg/day for adults, with a maximum of 20 mg/day in pregnancy and lactation. No dose of ergothioneine has been tied to a clinical outcome.

Can you get ergothioneine from mushrooms?

Yes — a large serving of oyster, king oyster or shiitake mushrooms supplies several milligrams of ergothioneine, for a fraction of a capsule's price. Because ergothioneine is retained for weeks, daily dosing is not strictly necessary.

Scientific references

Where to buy

Toniiq, L-Ergothioneine, 30 mg, 90 Capsules

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