Ergothioneine is a sulfur-containing amino acid that humans cannot synthesize themselves — we get it entirely from food, primarily mushrooms and some organ meats. What makes it unusual is that the body has a dedicated transporter protein (OCTN1) built specifically to absorb and hold onto it, which scientists take as a strong signal that it matters biologically. It accumulates in the highest concentrations in tissues that face the most oxidative stress, including the brain, bone marrow, liver, kidneys, and lens of the eye.

Ergothioneine neutralizes some of the most damaging free radicals in the body, including reactive oxygen and nitrogen species, without itself becoming unstable or pro-oxidant in the process. It also appears to protect mitochondria — your cells' energy generators — from damage, and may reduce the kind of low-grade inflammation that drives aging and chronic disease. Because it concentrates in sensitive tissues and refills slowly when depleted, maintaining adequate intake is thought to be protective over the long term.

Ergothioneine is available as isolated L-Ergothioneine capsules or tablets, as standardized mushroom extracts (particularly from oyster mushrooms or specialty cultivated varieties), and as a powdered supplement. Whole-food mushroom sources also deliver ergothioneine alongside complementary compounds like beta-glucans. The isolated form is used in most clinical research.

• Cognitive decline and brain aging
• Oxidative stress and cellular damage
• Inflammation (chronic, low-grade)
• Eye health and macular protection
• Liver health and detox support
• Mitochondrial health and energy
• Cardiovascular health
• Skin aging and UV damage
• Fatigue and physical resilience

• Cognitive decline associated with aging — population data links higher blood ergothioneine levels to significantly lower rates of decline over time
• Cardiovascular events — higher dietary intake has been associated with reduced cardiovascular mortality in large prospective cohort analyses
• Age-related cellular oxidative damage — sustained tissue loading appears to reduce cumulative oxidative injury in high-stress organs

• Mushrooms (especially oyster, shiitake, king oyster, and porcini) — By far the richest dietary source of ergothioneine — oyster and king oyster mushrooms can contain 5–13 mg per 100g cooked, making them essentially the primary human delivery vehicle for this compound.
• Chicken liver and organ meats — Animals accumulate ergothioneine from their plant and fungi-based feed; liver concentrates it more than muscle meat, offering a meaningful secondary animal-source contribution.
• Black beans and kidney beans — Legumes contain moderate ergothioneine levels relative to other plant foods, likely from soil bacteria during growth — a useful source for those who do not eat mushrooms regularly.
• Oat bran — Oats and oat bran contain detectable ergothioneine, likely from fungal and bacterial associations in soil, providing a small but consistent contribution to daily intake.
• Tempeh and fermented soy products — Fermentation by certain fungi and bacteria during tempeh production generates or concentrates ergothioneine, making it a meaningful plant-based source particularly for those following vegetarian or vegan diets.

• No significant adverse effects reported in human clinical trials at standard doses
• Mild gastrointestinal discomfort possible with high doses, as with most amino acid supplements
• No known toxicity level established in humans — very high doses have not been formally studied long-term

• Recommended daily: 5–30 mg per day of L-Ergothioneine; most clinical studies have used doses in the 5–25 mg range. Typical dietary intake from food is estimated at 1–5 mg/day for mushroom eaters.
• Best time of day: No strong preference established — morning or with a meal is practical and well-tolerated.
• With or without food: Best taken with food to support absorption via the OCTN1 transporter, which appears active during normal digestive transit.
• Time to effect: Measurable tissue loading takes approximately 4–8 weeks of consistent daily supplementation; some users report improved energy and reduced fatigue within 4–6 weeks.
• How long to take it: Long-term, continuous use appears to be the intended usage pattern given its role as a cumulative cellular protectant. No cycling protocol is required. Consistent daily intake is recommended for sustained tissue-level benefit.