What Are Adaptogens? Eight Ranked by Strength of Evidence

Adaptogens are plants and fungi grouped together by a claim about how they act, not by botany or chemistry: the claim that they raise general resistance to stress without the rebound of a stimulant. The word comes from Soviet pharmacology in 1947, and it is not a regulatory category in the EU or the UK. Below we rank eight of them, ashwagandha to shiitake, by how much published human trial evidence exists.

Almost every list of adaptogens herbs gives each one a paragraph of tradition, and none tells you that one of the eight has a dozen randomised trials behind it while another has essentially one.

Where the word came from, and why it is not a legal category

The term was established by the Soviet toxicologist N. V. Lazarev in 1947 to describe a substance that increases “non-specific” resistance to adverse influences, according to the European Medicines Agency reflection paper on the adaptogenic concept. Lazarev’s pupil I. I. Brekhman, with I. V. Dardymov, turned it into a definition.

That definition is usually quoted as three parts. The EMA paper lists four: an adaptogen is almost non-toxic; it is non-specific and acts by increasing resistance to a broad spectrum of adverse biological, chemical and physical factors; it tends to be a regulator with a normalising effect on the various organ systems; and its effect is more pronounced the deeper the pathological changes in the organism. That fourth clause is the one nobody quotes, and the one that makes the concept hardest to test.

The regulatory position is unambiguous. That paper, adopted by the Committee on Herbal Medicinal Products in May 2008, concludes that “the term is not accepted in pharmacological and clinical terminology that is commonly used in the EU” and is “not appropriate for a marketing authorisation”. An adaptogens definition exists in the literature, but the word carries no legal standing on a European label.

Individual plants can still hold an EU herbal monograph. Rhodiola rosea rhizome and root has one, in the traditional-use category, for temporary relief of symptoms of stress such as fatigue and sensation of weakness, restricted to adults over 18. That is a status attached to one plant, not recognition of the category.

How we ranked these eight adaptogens

The ranking is a statement about literature, not about bodies. Five things decided the order.

Number of randomised human trials. Not animal work, not cell studies, not a review citing a review. We counted controlled human trials identified by systematic reviews.

Size of the largest single trial. Twelve trials of 60 people is not one trial of 500. We name the largest we opened for each entry, with author, year, journal and participant count.

Independent synthesis. Whether anyone outside the supplement trade has pooled and graded the evidence. A Cochrane review counts for more than a manufacturer-funded single study.

What the reviewers said about quality. Where review authors state a certainty rating or a risk-of-bias verdict, we quote it, including when it is unflattering.

Documented harm signals. Published case reports and adverse-event data. An entry is ranked no lower for one, but the signal is named.

We do not rank by popularity. Two of the eight sit low despite being widely sold, and one of them is shilajit, which we sell.

The eight adaptogens, at a glance

1. Ashwagandha (Withania somnifera)
2. Rhodiola rosea
3. Reishi (Ganoderma lucidum)
4. Cordyceps
5. Maca (Lepidium meyenii)
6. Lion’s mane (Hericium erinaceus)
7. Shilajit
8. Shiitake (Lentinula edodes)

Ashwagandha (Withania somnifera)

Ashwagandha is the root of a nightshade shrub used in Ayurveda, sold in Europe as a standardised root extract in capsules, powders and adaptogens drinks. It has more randomised human trials behind it than the other seven entries combined.

Akhgarjand and colleagues (2022, Phytotherapy Research) pooled 12 randomised trials with 1,002 participants aged 25 to 48 and reported reductions in measured anxiety and stress scores against placebo. The largest individual trial we opened is Pandit and colleagues (2024, Nutrients): 131 chronically stressed adults enrolled, 98 analysed, at 125 mg, 250 mg and 500 mg daily over 8 weeks.

The catch is that the same meta-analysis rated its own certainty as low for both outcomes, with very high heterogeneity, and Björnsson and colleagues (2020, Liver International) described five cases of liver injury linked to ashwagandha-containing supplements. Standardisation and the European regulatory picture sit in our ashwagandha article.

Watch for:

• Published human trials: 12 randomised trials, 1,002 participants, pooled in 2022
• Largest trial we opened: Pandit and colleagues, 2024, Nutrients, 131 enrolled, 8 weeks
• Best-studied outcome: self-reported stress and anxiety scales, and morning cortisol
• Who should avoid it: pregnancy, breastfeeding, under 18s, liver disease, prescribed medication
• What it is not: a licensed medicine anywhere in the EU or the UK

Rhodiola rosea

Rhodiola is an arctic and alpine stonecrop, its root harvested at altitude. It is the only entry here with an EU herbal monograph, restricted to adults over 18.

Ishaque and colleagues (2012, BMC Complementary and Alternative Medicine) screened 206 articles and included 11 studies, ten of them randomised. Two of six trials on physical fatigue reported an effect, as did three of five on mental fatigue. The largest is Shevtsov and colleagues (2003, Phytomedicine), a single-dose study in 161 military cadets aged 19 to 21 comparing two doses of the SHR-5 extract against placebo.

The catch is stated plainly by the reviewers: every included study shows either a high risk of bias or reporting flaws that hinder assessment of its true validity. Eleven trials of unclear validity is a thinner base than the count suggests.

Watch for:

• Published human trials: 11 studies in the 2012 systematic review, ten of them randomised
• Largest trial we opened: Shevtsov and colleagues, 2003, Phytomedicine, 161 cadets, single dose
• Best-studied outcome: mental and physical fatigue under workload
• Who should avoid it: under 18s, pregnancy, breastfeeding, prescribed medication
• What it is not: approved on efficacy grounds, since its monograph rests on traditional use

Reishi (Ganoderma lucidum)

Reishi is a hard, varnished bracket fungus, inedible as food and taken as a hot-water or alcohol extract. Among the adaptogenic mushrooms it has had the most independent scrutiny.

Jin and colleagues (2016, Cochrane Database of Systematic Reviews) found five randomised trials in cancer patients. Shu and colleagues (2025, Frontiers in Nutrition) identified six more in athletes, roughly 220 participants, at 75 mg to 5 g daily. The largest single trial we opened is Tang and colleagues (2005, Journal of Medicinal Food): 132 patients with neurasthenia given a polysaccharide extract at 1,800 mg three times daily for 8 weeks.

The catch is the Cochrane verdict: the methodological quality of the primary studies was generally unsatisfying, reporting was inadequate, and the review found insufficient evidence to justify reishi as a first-line option in cancer care.

Watch for:

• Published human trials: 5 in the 2016 Cochrane review, plus 6 in athletes in a 2025 meta-analysis
• Largest trial we opened: Tang and colleagues, 2005, Journal of Medicinal Food, 132 patients, 8 weeks
• Best-studied outcome: fatigue and quality-of-life scales, plus blood cell markers in athletes
• Who should avoid it: pregnancy, breastfeeding, under 18s, cancer care without telling your oncologist
• What it is not: an adjunct any European regulator has approved

Cordyceps

Cordyceps is a genus of fungi that parasitises insects. Almost everything sold in Europe is Cordyceps militaris or cultivated mycelial biomass, not wild Ophiocordyceps sinensis.

Shu and colleagues (2025, Frontiers in Nutrition) identified four randomised trials of Cordyceps sinensis in athletes, roughly 87 participants, at 2 to 3 g per day or 10 mg per kilogram of body weight, over 2 to 12 weeks. Pooled, they reported changes in endurance measures, ventilatory threshold and peak oxygen uptake.

The catch is that the same authors flag likely publication bias: 13 of the 14 fungal trials they included reported favourable outcomes, which they say suggests the true effect size may be overestimated. Four small trials in athletes say nothing about anyone who is not one.

Watch for:

• Published human trials: 4 randomised trials in athletes, roughly 87 participants, pooled in 2025
• Largest trial we opened: none of the four exceeds a few dozen participants
• Best-studied outcome: aerobic capacity markers in trained adults
• Who should avoid it: pregnancy, breastfeeding, under 18s, prescribed medication
• What it is not: a studied option for sedentary adults, which is most buyers

Maca (Lepidium meyenii)

Maca is an Andean brassica root, eaten as a staple in Peru and sold in Europe as gelatinised powder or capsules.

Shin and colleagues (2010, BMC Complementary and Alternative Medicine) searched 17 databases and found four randomised trials. Two reported an effect on sexual function or desire, one found nothing in healthy cyclists, one reported an effect in men with erectile dysfunction. The largest we opened is Shin and colleagues (2023, World Journal of Men’s Health): 80 men with late-onset hypogonadism symptoms, 6 g daily or placebo for 12 weeks.

The catch is the reviewers’ own conclusion: the number of trials, the sample size and the average methodological quality were all too limited to draw firm conclusions.

Watch for:

• Published human trials: 4 randomised trials in the 2010 systematic review
• Largest trial we opened: Shin and colleagues, 2023, World Journal of Men’s Health, 80 men, 12 weeks
• Best-studied outcome: self-reported sexual desire and function questionnaires
• Who should avoid it: pregnancy, breastfeeding, under 18s, a thyroid condition without medical advice
• What it is not: a plant with any trial supporting the slimming claims attached to it online

Lion’s mane (Hericium erinaceus)

Lion’s mane is an edible white toothed fungus growing on hardwood, one of the few adaptogenic mushrooms you can buy fresh and cook. Its research base is small, recent and dominated by pilot studies.

Mori and colleagues (2009, Phytotherapy Research) randomised 30 Japanese adults aged 50 to 80 with mild cognitive impairment to 3 g of dried powder daily or placebo for 16 weeks, and reported higher scores on a cognitive function scale at weeks 8, 12 and 16 that fell back 4 weeks after intake stopped. Docherty and colleagues (2023, Nutrients) gave 1.8 g to 41 healthy adults and called their own study a pilot.

The catch is scale. The largest study we could open has 41 participants, and the 2025 meta-analysis of fungal supplements in athletes searched for lion’s mane and found no trial meeting its criteria.

Watch for:

• Published human trials: a handful of small randomised studies, none larger than about 50 people
• Largest trial we opened: Docherty and colleagues, 2023, Nutrients, 41 healthy adults, 28 days
• Best-studied outcome: cognitive test scores in mild impairment and in healthy young adults
• Who should avoid it: pregnancy, breastfeeding, under 18s, anyone with a known mushroom allergy
• What it is not: a substance with any large or long trial behind it

Shilajit

Shilajit is not a plant. It is a dark resin that seeps from rock at altitude, largely decomposed plant matter rich in fulvic and humic substances, and the only geological material here. Its full definition sits in our shilajit pillar.

Two randomised placebo-controlled trials are worth naming. Pandit and colleagues (2016, Andrologia) gave 250 mg of purified shilajit twice daily for 90 days to healthy men aged 45 to 55 and measured androgenic hormones. Keller and colleagues (2019, Journal of the International Society of Sports Nutrition) randomised 63 recreationally active men to 250 mg, 500 mg or placebo for 8 weeks, measuring strength retention after a fatiguing leg protocol.

The catch is that two trials is two trials. Neither has been independently replicated, neither ran past 90 days, and no systematic review pools them. Purity is a live question with a mined material, which is why heavy metal testing has its own article.

Watch for:

• Published human trials: 2 randomised placebo-controlled trials, no systematic review pooling them
• Largest trial we opened: Keller and colleagues, 2019, J Int Soc Sports Nutr, 63 men, 8 weeks
• Best-studied outcome: strength retention after fatigue, and serum androgens in men 45 to 55
• Who should avoid it: haemochromatosis or another iron-overload condition, pregnancy, breastfeeding, under 18s
• What it is not: a substance studied in women, in older adults, or beyond 90 days

Shiitake (Lentinula edodes)

Shiitake is a cultivated edible mushroom and the entry with the weakest claim to the adaptogen label. It appears on adaptogens lists by association with the other fungi.

The most relevant controlled human study we opened is Dai and colleagues (2015, Journal of the American College of Nutrition): a 4-week dietary intervention in 52 healthy adults aged 21 to 41 eating 5 g or 10 g of whole dried mushroom daily, measuring white blood cell proliferation markers. That is a food study, not an adaptogen trial.

The catch is that no body of randomised trials tests shiitake against stress, fatigue or resistance. It is a good mushroom with a thin file, and any page listing it beside ashwagandha without saying so is not being straight with you.

Watch for:

• Published human trials: effectively one relevant controlled dietary study, no stress or fatigue trials
• Largest trial we opened: Dai and colleagues, 2015, J Am Coll Nutr, 52 adults, 4 weeks
• Best-studied outcome: white blood cell activity markers after 4 weeks of eating the mushroom
• Who should avoid it: a mushroom allergy, pregnancy, breastfeeding, under 18s
• What it is not: a substance with any published trial supporting an adaptogenic effect

The comparison table

Adaptogen	Human trials	Largest trial we opened	Best-studied outcome	Avoid if	Not established
Ashwagandha	12 randomised, 1,002 people	Pandit 2024, 131 enrolled	Stress and anxiety scales	Liver disease, pregnancy	Any licensed medical use
Rhodiola	11 studies, ten randomised	Shevtsov 2003, 161 cadets	Mental and physical fatigue	Under 18, pregnancy	Efficacy free of bias risk
Reishi	5 in Cochrane, 6 in athletes	Tang 2005, 132 patients	Fatigue and quality of life	In cancer care	First-line clinical use
Cordyceps	4 randomised, about 87 people	None above a few dozen	Aerobic capacity in athletes	Pregnancy, on medication	Any effect in non-athletes
Maca	4 randomised	Shin 2023, 80 men	Sexual desire questionnaires	Thyroid condition, pregnancy	Slimming claims of any kind
Lion’s mane	A handful, all small	Docherty 2023, 41 adults	Cognitive test scores	Mushroom allergy, pregnancy	Anything at scale or length
Shilajit	2 randomised	Keller 2019, 63 men	Strength retention, androgens	Iron overload, pregnancy	Any data in women
Shiitake	One dietary study	Dai 2015, 52 adults	White cell activity markers	Mushroom allergy, pregnancy	Any adaptogenic effect

The pattern is the honest answer to “which is the best adaptogen”: one entry has a real evidence base, three have a modest one, and four are running on a handful of small studies.

Do adaptogens really work, and how long do they take?

These are what readers type before buying adaptogens supplements, in any language.

It depends entirely on which one, and the table above is the answer. No finding applies to adaptogens as a class, because the class is a 1947 concept rather than a mechanism, and the EMA has said the principle needs further clarification and study. Anyone who tells you adaptogens work has told you nothing, because they have not said which plant, which dose, which outcome or which population.

We cannot tell you what you will feel, but we can tell you what the researchers did. The trials above ran 4 weeks for shiitake, 28 days for lion’s mane in healthy adults, 8 weeks for ashwagandha, reishi and shilajit, 12 weeks for maca, and 16 weeks for lion’s mane in older adults. The durations say weeks, not days.

What is not known, and who should not take these

The honest limits are the most useful part of this page. Nobody has run a head-to-head trial of these eight, so “the most powerful adaptogen” has no evidential answer and anyone ranking them by strength is guessing. Nobody has established a dose that generalises across products: extracts are standardised differently, and a milligram of one is not a milligram of another. Almost none of the trials ran past 16 weeks, so long-term use is unstudied rather than shown to be safe. Most used small, healthy, often young populations, which is rarely the person buying.

Side effects are poorly catalogued as a group. The clearest documented signal is the Björnsson case series in Liver International: five patients who developed jaundice 2 to 12 weeks after starting ashwagandha-containing supplements, with liver tests normalising within 1 to 5 months in the four followed up. The 2025 fungal meta-analysis notes that adverse-event reporting across its trials was not standardised, so an absence of reported harm is not evidence of an absence of harm.

Do not take any of these if you are pregnant or breastfeeding. Do not give them to children: the EU monograph for rhodiola restricts it to adults over 18, and that restriction is the norm rather than the exception. If you take prescribed medication or have a diagnosed condition, speak to a doctor or pharmacist first, because herb and drug interactions are real and under-researched. Anyone with haemochromatosis or another iron-overload condition should avoid shilajit, and anyone with a mushroom allergy should avoid the fungi. Women should read the women-specific evidence before starting shilajit, because the trials were done in men.

What to do with this

The decision is narrower than the marketing suggests. Two questions matter: does the plant have more than a couple of controlled human trials behind it, and does the product state its extract, its dose per serving and its testing? Everything else is branding: no European rule defines adaptogens as a category.

If you want the deepest literature, that is ashwagandha, and dose and timing are answered in its own guide. If you want the mushroom side of the category, or the shilajit pairings, our capsule range puts 250 mg of a named active alongside 250 mg of shilajit extract per capsule, and the label says exactly that and nothing more. We would rather you bought one thing you understand than five you do not.