A widely eaten culinary mushroom and the source of lentinan, a purified beta-1,3-glucan used as an injectable adjuvant cancer medicine in Japan. Oral supplements contain mushroom powder or hot-water extract, not lentinan.
The evidence separates cleanly along the route of administration. Injected lentinan has been used in Japan since 1985 alongside chemotherapy for gastric cancer, with meta-analyses reporting modest survival differences — a pharmaceutical, given intravenously, under oncological care. Oral shiitake is a food with a decent beta-glucan content and a small human literature: a University of Florida study reported changes in immune markers after four weeks of daily shiitake consumption, and a handful of trials look at cholesterol. Neither supports the claims made for shiitake capsules. Shiitake also causes a distinctive and genuinely unpleasant skin reaction that most people have never heard of.
Sometimes percentage beta-glucan; lentinan itself is a defined pharmaceutical preparation not available as a supplement — a product without this marker may not resemble what was studied.
Also known as
Shiitake, Lentinan, Xiang gu, Black forest mushroom
Regulation: Lentinan is an approved injectable medicine in Japan and is not available in the US or Europe. Oral shiitake products are dietary supplements with no pre-market efficacy review.
What the research used
The amounts, forms and durations published trials of Shiitake and lentinan actually administered.
These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.
Studied for Immune marker study with whole food
5–10 g
Not enough
Dried shiitake, rehydrated and eaten daily · 4 weeks
A small study in young adults reporting changes in gamma delta T cell measures and inflammatory markers. It used food, not capsules, and had no control group taking a different mushroom.
Studied for Lentinan as adjuvant cancer therapy (Japan)
The licensed injectable protocol. It is included to make the point that the oncology evidence for lentinan is intravenous and pharmaceutical, and has no bearing on an oral capsule.
This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.
When it was taken
Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.
None of the timings below were directly compared in a trial. They reflect how the research happened to dose, or what the pharmacology implies — which is not the same as a timing being better.
🕐Any time
Not enough
No timing comparison exists for oral shiitake products.
Timing was not directly compared. This reflects convention or how the compound behaves in the body, not a trial showing this window works better.
The evidence in depth
Best supported: Not enough
What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.
A small study found changes in immune cell measures after four weeks of eating shiitake daily. These were laboratory markers in a handful of healthy young people with no clinical endpoint, and oral supplements have not been tested at all.
What may be going on: Lentinan is a beta-1,3-glucan that activates innate immune receptors. Oral beta-glucans are poorly absorbed intact, which is why the pharmaceutical is injected.
Not enough evidence. Not enough human research to say anything useful yet.
Deep research mode adds each paper’s own conclusion and stated limitations.
Things to know
Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.
Worth knowing
Shiitake dermatitis from raw or undercooked mushrooms
Eating raw or lightly cooked shiitake causes a striking whip-like rash of linear red streaks across the trunk and limbs, usually appearing a day or two later and lasting one to two weeks. It is attributed to lentinan surviving inadequate cooking and is well documented in Japan, Europe and North America. Thorough cooking is what avoids it.
Worth knowing
The lentinan evidence is injectable and not transferable
Marketing that quotes lentinan survival data for an oral shiitake capsule is describing a different drug given by a different route in a hospital. Oral beta-glucan is largely not absorbed intact, which is precisely why the medicine is injected.
Allergy
Occupational and dietary reactions
Shiitake spores cause an occupational lung reaction in growers, and contact dermatitis and asthma have been reported in handlers. Ingestion reactions in sensitised people also occur.
Too much
Digestive upset and photosensitivity
Bloating and loose stools are common with concentrated extracts. Photosensitivity has also been reported, which matters alongside the dermatitis risk.
In the food catalogue
The whole-food form, where one exists. The evidence for a concentrated extract rarely transfers to the food, or the other way round — these are cross-links, not equivalents.