Reishi: The Immortality Mushroom of Chinese Medicine, What the Research Says

In traditional Chinese medicine, one mushroom has earned a rare title: Reishi, or by its Chinese name Lingzhi, has been called the "Mushroom of Immortality" or "Mushroom of Eternal Life" for thousands of years. Ancient paintings depict it in the hands of emperors and immortals, and it was considered so precious that it was reserved for the upper class alone. Today, it is sold in every health food store as a supplement for immune support, restful sleep, and reducing fatigue and stress.

The poetic name and millennia-old tradition are impressive, but this is precisely where caution is needed. A historical aura is not scientific evidence, and the real question is what controlled human trials show about reishi, not what was believed about it two thousand years ago. The answer, as we will see, is complex: there is an interesting biological basis, some promising results, but also a limited body of evidence of low quality, alongside safety issues that should not be ignored. In this article, we will separate myth from science and explain why we rated reishi yellow.

What is Reishi?

Reishi is the Japanese name for the mushroom Ganoderma lucidum, a reddish, shiny, woody mushroom that grows on tree trunks. Unlike soft edible mushrooms, reishi is hard and woody like wood, so it is not eaten directly but extracted into a tincture, powder, or tea. Here is what is important to understand about it:

• It is rich in beta-glucans. These are complex sugars (polysaccharides) from the mushroom's cell wall, considered the main component affecting the immune system in laboratory studies.
• It contains unique triterpenes. Ganoderic acids are bitter compounds with anti-inflammatory and antioxidant activity in studies, and they are considered the chemical hallmark of the mushroom.
• It is used in Chinese medicine as an "adaptogen." Traditionally, it was given for general strengthening, calming, sleep, and longevity, without being designated for one specific disease.
• Note: There is a difference between powder and extract. A concentrated extract that has been steeped in water or alcohol is considered higher quality and safer than raw mushroom powder, and this distinction is also relevant to safety, as we will see later.

It is important to understand that reishi is fundamentally different from a simple vitamin supplement. It does not provide a missing nutrient but seeks to regulate processes in the body, primarily in the immune system, and this is precisely why its effects are subtle, context-dependent, and harder to measure. It is sold in capsules, powder, liquid extract, and tea, at a moderate price, and often as part of a medicinal mushroom blend.

The Connection to the Immune System: The Mechanism

Most scientific interest in reishi centers on the immune system, so it is worth understanding the proposed mechanisms. The central idea is that the beta-glucans and triterpenes in the mushroom interact with immune cells and alter their activity, which is why reishi is described as a "trainer" of the immune system rather than a general suppressor or stimulator.

First mechanism: beta-glucans and activation of immune cells. Beta-glucans are recognized by receptors on the surface of innate immune cells (like macrophages and dendritic cells), and this binding may enhance their activity. Studies have observed an increase in certain populations of lymphocytes and T cells. This is the theoretical basis for the claim that reishi "boosts immunity," although the transition from laboratory measurement to proven clinical benefit is far from self-evident.

Second mechanism: triterpenes and anti-inflammatory activity. Ganoderic acids have been demonstrated in laboratory studies to affect inflammatory mediators and oxidative stress. This activity is relevant to the theory that reishi supports general health and healthy aging, but almost all of this data comes from test tubes and animals, not humans.

Third mechanism: effects on the brain, sleep, and stress. Traditionally, reishi was given for calming and improving sleep, and some animal studies suggest a possible calming effect and shortened time to fall asleep. The exact mechanism is unclear, but this property is part of reishi's identity as an "adaptogen" attributed with the ability to help the body cope with stress. Here, it must be emphasized that the human evidence for sleep and stress is still thin.

Current Evidence

Study 1: Reishi and Cancer, Cochrane Review by Jin et al. 2016

This is the most important and balanced evidence regarding reishi. In 2016, Jin et al. published a systematic review and meta-analysis in the Cochrane Library that pooled 5 randomized controlled trials, involving about 373 cancer patients, which examined reishi alongside conventional treatment.

The findings are complex. On one hand, reishi showed an ability to stimulate the immune response: a significant increase in the percentages of CD3, CD4, and CD8 lymphocytes, and NK cell (natural killer cells) activity increased slightly. Additionally, patients receiving reishi reported better quality of life after treatment. On the other hand, and critically, the researchers emphasized that reishi is not a standalone cancer treatment and there is no justification to recommend it as a first-line therapy, and that the quality of evidence is low due to small studies and methodological issues. Mild side effects like nausea and insomnia were also reported. The fair conclusion: reishi may function as a supportive adjunct that improves immune function and quality of life, but never as a substitute for oncological treatment.

Study 2: Reishi and Neurasthenia (Nervous Exhaustion), Trial by Tang et al. 2005

Another area of research is chronic fatigue and feelings of exhaustion. In 2005, Tang et al. published a double-blind, placebo-controlled trial involving 132 patients with neurasthenia (nervous exhaustion), who took a reishi polysaccharide extract or placebo for 8 weeks.

The results were positive but moderate: In the reishi group, there was a greater reduction in fatigue (about 28% from baseline) and a greater increase in overall well-being compared to placebo. However, it is important to remember that this is a single trial, in a specific population, with a specific preparation, so it cannot be generalized to everyone who feels tired. It is an encouraging hint, not strong proof.

Study 3: Reishi, Mood, and Quality of Life, Additional Small Trials

Beyond the two main studies, additional small trials have been published on the effect of reishi on mood and quality of life, including in women with fibromyalgia and breast cancer patients with treatment-related fatigue. Some of these studies showed improvement in well-being, fatigue, and mood measures, but almost all are very small, some lack a strong control group, and therefore their evidentiary weight is limited.

The cumulative picture repeats itself across all areas: there is a promising direction, a plausible biological mechanism, but there is not yet a large, independent, high-quality body of evidence to substantiate the claims. This is precisely why reishi remains a "yellow" supplement and not "green."

What About Aging, Heart, and Blood Sugar?

Reishi is also often marketed in the broader context of longevity, heart health, and blood sugar balance, but here the evidence is even weaker. Early studies, mostly in animals or test tubes, have examined a possible effect on blood pressure, blood lipids, and blood sugar levels, but the results in humans are few, mixed, and inconsistent. Systematic reviews examining reishi for treating cardiovascular risk factors in type 2 diabetes patients did not find sufficient evidence to support such use.

The antioxidant and anti-inflammatory activity attributed to triterpenes is indeed theoretically relevant to healthy aging, but "theoretically relevant" and "clinically proven" are two completely different things. As of today, there is no solid basis to recommend reishi as an anti-aging supplement, and certainly not as a substitute for the proven foundations of longevity. The bottom line is the same: the mushroom is biologically interesting, but expectations should remain realistic.

Should You Start Taking Reishi?

This is precisely why we rated reishi yellow. On one hand, there is a rich tradition, a plausible biological mechanism, and some promising results. On the other hand, the quality of evidence is low, and there are real safety issues that must be known before starting. Here are the considerations:

• Blood-thinning effect. Reishi has mild anticoagulant activity, so anyone taking blood-thinning medications (like warfarin or aspirin at therapeutic doses) needs special caution, and intake should be stopped before planned surgery due to an increased risk of bleeding.
• Rare reports of liver damage. Isolated cases of liver toxicity have been described, attributed specifically to the use of raw reishi powder, while controlled extracts have a better safety profile. This is a practical reason to prefer an extract from a reliable brand over cheap, uncontrolled powder.
• Immune stimulation and autoimmune diseases. Precisely the property that makes reishi interesting—the ability to stimulate immune cells—requires caution in people with autoimmune diseases (such as lupus, multiple sclerosis, or rheumatoid arthritis), as immune stimulation could worsen the condition.
• Mild side effects. Nausea, dry mouth, insomnia, dizziness, or gastrointestinal discomfort have been reported, especially at high doses and with long-term use.

Beyond that, there are groups that should avoid or consult a doctor. Pregnant or breastfeeding women should avoid reishi due to a lack of sufficient safety data. People with bleeding disorders, those about to undergo surgery, those taking immunosuppressive drugs (e.g., after a transplant), and those with liver disease should get medical approval before taking it. And as always: reishi is never a substitute for medical treatment, especially not for cancer, even if tradition calls it the "Mushroom of Immortality."

What to Take Away from the Research?

1. If choosing reishi, prefer an extract from a reliable brand. Choose a standardized extract with a defined percentage of beta-glucans, not cheap raw mushroom powder, also for liver safety reasons.
2. Don't expect miracles; treat it as a supportive addition. The best evidence points to moderate improvement in fatigue, quality of life, and immune markers, not disease cure.
3. If you are taking blood thinners or are about to have surgery, consult or avoid. Reishi's anticoagulant activity is real and requires caution.
4. If you have an autoimmune disease, do not start without a doctor. The immune stimulation could work against you.
5. Cancer patients: only in coordination with your oncologist. Reishi may serve as a supportive addition for quality of life and immune function, but never in place of treatment, and it is necessary to ensure there is no interaction with chemotherapy.

For those who want to try reishi from a reliable source, you can purchase reishi on iHerb and choose a standardized extract with lab testing. But remember: with medicinal mushrooms, the quality of the preparation is everything. To check which supplements are truly suitable for your health goals, including immune support, based on your age and condition, you can use our personal supplement checker that rates each supplement according to the quality of evidence.

The Broader Perspective

Reishi is an excellent example of the gap between millennia-old tradition and modern science. On one hand, it is a mushroom with a truly interesting chemical composition, a plausible immune mechanism, and some controlled trials showing moderate benefit in fatigue, quality of life, and immune function. On the other hand, the image of the "Mushroom of Immortality" is greatly inflated compared to what the evidence supports. When you add the safety issues—anticoagulant activity, reports of liver damage from raw powder, and immune stimulation—you get a classic profile of a yellow supplement: promising under the right conditions, but requiring informed choice and caution.

The practical lesson is twofold. First, the poetic name and tradition are not a substitute for evidence, and when choosing a supplement like reishi, what matters is the quality of the preparation and its suitability for your personal health condition, not the historical aura. Second, it is important to remember that a single supplement, no matter how ancient and respected, does not replace the fundamentals. Strong immunity and longevity are built from sleep, nutrition, physical activity, stress management, and avoiding smoking, and reishi can be, at best, a small and supportive contributor. And that is precisely the perspective we hold here: to rate each supplement according to what the science actually shows, when it is promising, and when it is better to remain cautious.

References:
Jin X. et al., Ganoderma lucidum (Reishi mushroom) for cancer treatment, Cochrane Database of Systematic Reviews, 2016, Issue 4. Art. No.: CD007731 (DOI: 10.1002/14651858.CD007731.pub3)
Tang W. et al., A randomized, double-blind and placebo-controlled study of a Ganoderma lucidum polysaccharide extract in neurasthenia, Journal of Medicinal Food, 2005;8(1):53-58 (DOI: 10.1089/jmf.2005.8.53)
Zhao H. et al., Spore Powder of Ganoderma lucidum Improves Cancer-Related Fatigue in Breast Cancer Patients Undergoing Endocrine Therapy: A Pilot Clinical Trial, Evidence-Based Complementary and Alternative Medicine, 2012