Lichen

Other Names

archilBarba de CapuchinoBarbe de JupiterBarbe de Saint Antoinebear hair lichenbeard lichenbeard mossblack tree lichenBritish soldiers lichenBryoria fremontiicaribou lichencaribou mossCentrariaCetraria islandicachharilaCladina rangiferinaCladoniaCladonia rangiferinaCoralloidescrotalcrottlecudbeardagad phooledible horsehair lichenerba rissaeryngo-leaved liverwortEvernia prunastrifjallagrashorsehair lichenIceland lichenIceland mossIslaendisch MoosIslandslavIslanninjäkäläIwa-takeiwatakeLetharia vulpinalichen d'Islandelichen-forming fungusLichene Islandicolichenized fungilichenized fungusliquén de IslandiaLobaria pulmonarialung lichenlung mosslungwort lichenmap lichenMousse d'Arbremousse d'IslandeMusgo de los Arbolesoak mossoakmossold man's beardorchilorchillaParmeliapixie cups lichenPseudevernia furfuraceapuklérka Islandskárathapureindeer lichenreindeer mossRhizocarpon geographicumrock flowerrock tripeSargyangma lichen (Nepalese traditional use)stone flowersymbiotic organism (fungus-algae)thallophytetree mosstree moss (Pseudevernia furfuracea)tree's dandrufftrue Iceland lichenUmbilicariaUsneaUsnea barbataUsnea floridaUsnea hirtaUsnea longissimaUsnea plicataUsnéeUsnée BarbueUsnée Fleuriewolf lichenwoman's long hairXanthoria parietinayellow wall lichen

Synopsis

Lichen as a Dietary Supplement and Natural Medicinal Ingredient

1. Identity, Taxonomy, and Natural Sources

Lichens are a world-widespread consortium of fungal and photosynthetic partners. More precisely, usnic acid is a dibenzofuran derivative naturally present in lichens — organisms resulting from the symbiosis between a fungus and a cyanobacterium, or an alga. Lichens represent a morphological unit of fungi and algae that live together in a symbiotic relationship. The fungus forms the hyphae that adhere to the soil, which the lichen uses to absorb water and nutrient salts, while the algae is responsible for photosynthesis, which plants use to build up their energy-rich compounds.

Lichens are not classified as plants in the strict botanical sense, though they grow in plant-like forms and occupy similar ecological niches. Lichens are slow-growing organisms, but they are found in different kinds of habitats throughout the world. Lichens are particularly abundant in cool, humid places, but can also withstand drought, extreme heat, and extremely low temperatures for extended periods of time.

The term "lichen" in dietary supplement and food contexts encompasses a large number of species. Key species of medicinal and nutritional relevance include:

Cetraria islandica (L.) Acharius s.l. — commonly called Iceland moss. Iceland moss is widespread in the boreal, alpine, and arctic regions of the Northern Hemisphere, including Iceland. It is a fruticose, or shrub-like and bushy, lichen growing loosely on the soil to a height of 3–4 inches. The thallus is channeled or rolled into thin, branched tubes, which terminate in flattened lobes fringed with minute papillae, rarely more than 5 mm wide.
Usnea spp. — a genus of pendant, hair-like lichens used across many cultures. Usnic acid is abundant in lichen genera such as Usnea, Ramalina, Cladonia, Evernia, Alectoria, Lecanora, Flavocetraria, and Vulpicida.
Cladonia spp. (including Cladonia rangiferina, reindeer lichen) — widely distributed Arctic and sub-Arctic species.
Lobaria pulmonaria — a foliose (leaf-like) lichen of temperate forests.
Parmelia/Parmotrema spp. — used in Asian and European traditions.
Pseudevernia furfuracea — known as tree moss, used since antiquity. Pseudevernia furfuracea, commonly known as Tree Moss, has been used from the Ancient Egyptian era to the Modern World.

Morphological Growth Forms

Lichens are broadly categorized into three main morphological types relevant to their collection and preparation:

Fruticose — shrubby, branching, upright or pendant (e.g., Usnea, Cetraria islandica)
Foliose — flat and leaf-like, loosely attached to substrate (e.g., Lobaria pulmonaria, Parmotrema)
Crustose — tightly adhering crust on rock or bark

Common Preparations and Dosage Forms

The HMPC conclusions cover Iceland moss preparations obtained by drying and comminuting (reducing into tiny pieces) the thallus, or by putting the plant material in a solvent (such as ethanol or water) to dissolve compounds and form a liquid extract. The solvent may then be partially evaporated to obtain a soft extract. Herbal medicines containing these Iceland moss preparations are usually available as herbal tea to be drunk and in solid or liquid forms to be taken by mouth or applied to the lining of the mouth.

Herbal preparation varies from decoctions, tinctures and aqueous extracts to infusions. In modern commerce, lichen-derived ingredients appear in several additional forms:

Standardized extracts in capsules and tablets (particularly Usnea and Iceland moss)
Tinctures (ethanol-based liquid extracts)
Herbal teas prepared from dried, whole thallus
Powders (dried and milled thallus)
Isolated compounds — most notably usnic acid, which is an abundant characteristic secondary metabolite of lichens and the earliest lichen compound used commercially. It has diverse pharmacological activities, such as anti-inflammatory, antibacterial, antiviral, anticancer, antioxidant, and photoprotective effects, and promotes wound healing. It is widely used in dietary supplements, daily chemical products (fodder, dyes, food, perfumery, and cosmetics), and medicine.
Lichen-derived vitamin D3 supplements, sourced from specific lichen species that biosynthesize cholecalciferol

2. Traditional and Historical Use

Edible lichens are nutritious sources of health-promoting bioactive compounds utilized as ethnic foods and traditional medicine for ages and documented across universal pharmacopoeia. Lichens are used in traditional medicines by cultures across the world, particularly in temperate and arctic regions.

Iceland and Northern Europe (Cetraria islandica)

The medicinal lichen Cetraria islandica, also known as Iceland Moss, has been included in European Pharmacopoeias from the 1600s and traditionally used to treat lung diseases and inflammation of oral and pharyngeal mucosa. In Iceland it is also used in folk medicines to treat cold symptoms and other minor ailments as dried and pulverized lichen (sometimes in capsules), as herbal tea or as a traditionally prepared milk soup (lichen boiled in milk).

In Iceland, it featured in various traditional dishes, including soups, porridges, sausages, and was even added to skyr (a type of curd). An alcoholic beverage known as Cetraria islandica schnapps was also produced from this lichen. In Iceland, C. islandica has been used to relieve both gastric and duodenal ulcers. Decoctions of C. islandica were used to treat colds in Finland.

During the beet sugar scarcity in Russia in 1942, Iceland moss was also industrially used to extract glucose.

The Himalayas, China, and South Asia

Lichens are used in traditional medicine, food, and various other ethnic uses by cultures across the Himalayas and southwestern parts of China. Evidence-based knowledge from historical and modern literatures and investigation of ethnic uses from 1990 proved that lichen species used as medicine in the Himalayas and southwestern parts of China totaled to 142 species; furthermore, 42 species were utilized as food.

Today, ethnic groups inhabiting the mighty Himalayas (Bhutan, China, India and Nepal) primarily adapt the classical systems of medicine following Ayurveda, Siddha, Unani, Traditional Chinese Medicine (TCM) and Amchi practices and continue their traditional uses of lichens for food, beverages and traditional medicine.

In Nepal specifically, the Kiraat religious group (Limbu and Rai) is using three lichen species (Everniastrum nepalense, E. cirrhatum, Parmotrema cetratum) mainly for their food value, while the Buddhism religious group preferred lichens (Heterodermia diademata, Usnea longissima, and Thamnolia vermicularis) for medicinal and ritual and spiritual values.

In Nepal, Limbu and Rai peoples boil species like Everniastrum cirrhatum and Parmotrema cetratum with wood ash, dry them, and grind into powder mixed with barley or wheat flour in a 1:3 ratio to make bread or sausages served during festivals. In Bhutan, Lobaria species are similarly prepared as vegetable curries or porridges, collected seasonally and valued for their mineral content when combined with local grains.

Antimicrobial Use of Usnea Species

Usnea species have been used as antimicrobials since 101 B.C. The most commonly used genus of lichen is Usnea, which is used across the world for medicine, although it is often used synonymously with other arboreal hair lichens. Lichen metabolites have been employed in traditional therapies for treating external burns, wounds, asthma, colds, tuberculosis, gastritis, and other ailments in humans and animals.

Ancient Egyptian Use

Pseudevernia furfuracea, commonly known as Tree Moss, has been used from the Ancient Egyptian era to the Modern World. Archaeological evidence shows tree moss and related lichens were incorporated in Egyptian cosmetics and ritual preparations.

Global Scope

A total of 60 different genera of lichens have been documented for use in traditional medicines. There are more records of lichen use among cultures in temperate and arctic areas and less in the tropics. The medicinal use of lichen has been known in traditional systems including herbal, Chinese, and homeopathic medicines.

3. Nutritional Composition

Lichens have a huge significance which is used in nutrition due to the bioactive components within. Lichen is a nutrient-dense resourceful diet and has long been used as food; also, these valuable natural resources are now being utilized for a wide range of other purposes.

Many of the lichens are edible, having the protein content (5.95–16.2%), carbohydrate content (53.2–79.08%), fat content (1.3–6.5%), crude fibre (5.38–16.36%) and ash (4.00–12.1%), which are safe to eat.

Cetraria islandica (Iceland moss) contains up to 82.5% carbohydrates including the polysaccharide lichenin, and has been used in Northern Europe for porridges, breads, and soups.

While most lichens are bitter and low in calories, certain species offer carbohydrates, proteins, fibers, vitamins, and minerals, making them valuable in traditional diets after proper preparation to neutralize toxins.

Regarding mineral content, lichens include a variety of important nutrients; however, they can accumulate air pollutants easily. Meli et al. reported that arsenic, cadmium, lead, and other toxic elements are present in Cetraria islandica, but stated that the low quantities are not dangerous to human health. The amounts of Pb in Swiss lichens were especially high in material collected close to busy roads and at tourist sites, which has implications for wild-harvested supplement safety.

Research on the nutritional analysis of lichens has been neglected by researchers due to their slow growth rate and there are many difficulties in culturing them in vitro. Theoretically, it is known that many lichens have nutritive value, but research on edible lichens is still needed to establish their nutritional potential.

4. Key Chemical Constituents and Active Compounds

Lichens have about 1050 different chemical substances including aliphatic acids, depsides and depsidones, diterpenes, dibenzofurans, naphthoquinones, anthraquinones, pulvinic acids, usnic acids, and xanthones. The major classes of secondary metabolites relevant to dietary supplement use are described below.

4.1 Usnic Acid

Since usnic acid (UA) was isolated from lichen metabolite in 1844, a lot of studies were conducted on it and now it became commercially available in the market. Usnic acid is one of the most common and abundant lichen metabolites, well known as an antibiotic, but also endowed with several other interesting properties. On the basis of the existing literature, usnic acid seems to be an exclusive lichen product.

Usnic acid is a dibenzofuran-based compound that exists as two enantiomers, (+)-usnic acid and (−)-usnic acid. Both the (+) and (−) enantiomers of usnic acid are effective against a large variety of Gram-positive (G+) bacterial strains, including strains from clinical isolates, irrespective of their resistant phenotype.

4.2 Depsides and Depsidones

The wide range of pharmacological activities and imaginable applications in medicinal and pharmaceutical chemistry in lichen are attributed to the presence of secondary metabolites like atranorin and usnic acid.

Key compounds in this class include:

Atranorin — a depside found in many lichen species. Atranorin and (+)-iso-usnic acid showed an inhibitory effect on nitric oxide (NO) levels in lipopolysaccharide (LPS)-stimulated macrophages, a key mechanism of anti-inflammatory action.
Parietin — an anthraquinone found prominently in Xanthoria parietina. Fazio et al. described the antiviral activity of parietin isolated from Teloschistes chrysophthalmus against some Junin and Tacaribe arenaviruses.
Gyrophoric acid — a tridepside with documented cytotoxic and antioxidant properties.
Evernic acid, physodic acid, salazinic acid, fumarprotocetraric acid, divaricatic acid — atranorin, fumarprotocetraric acid, gyrophoric acid, lecanoric acid, physodic acid, protocetraric acid, stictic acid, usnic acid, obtusatic acid, methyl evernate, divaricatic acid, and parietin showed relatively strong antimicrobial effects against numerous bacteria and fungi, among which were human pathogens.

4.3 Lichen Polysaccharides

Pharmacological investigations of the lichen Cetraria islandica have shown that polysaccharides as well as low molecular weight constituents exhibit significant biological activity. Key polysaccharides include:

Lichenin (lichen starch) — a β-glucan polysaccharide; the primary structural carbohydrate of Cetraria islandica, responsible for its mucilaginous, demulcent properties.
Isolichenan — an α-glucan; a soluble polysaccharide, isolichenan, where the ratio of α(1→3) to α(1→4) linkages can vary between about 3 and 5.2, is present in large amounts in many lichens such as the Iceland moss Cetraria islandica.
Galactomannan — a polysaccharide with a backbone of (1→6)-linked α-D-mannopyranosyl and α-D-(1→6)-galactopyranosyl units has been isolated from an alkali extract of Iceland moss. The galactomannan (mean Mr = 18 kDalton) exhibited pronounced enhancement of phagocytosis in both in vitro and in vivo assays.

Several polysaccharide fractions, isolated from a hot aqueous extract of Iceland moss by ethanol fractionation and ion-exchange chromatography, exerted significant activity in several immunological assays.

4.4 Anthraquinones and Other Pigments

Polysaccharide fraction compounds, parietin, usnic acid, atranorin, calycin compounds, and rhizocarpic acid are lichen metabolites that have the potential to be used as antivirals.

4.5 Mechanisms of Action

Proposed mechanisms of action for the most-studied compounds include:

Antimicrobial mechanism of usnic acid: Usnic acid-induced hepatotoxicity may result from oxidative stress by inhibiting mitochondrial oxidative phosphorylation, thereby causing an increase in reactive oxygen species. This same mechanism — uncoupling of mitochondrial oxidative phosphorylation — was the basis for its promotion as a "fat burner" in weight loss supplements, though it is also responsible for its toxicity.
Anti-inflammatory mechanism: Atranorin and (+)-iso-usnic acid showed an inhibitory effect on nitric oxide (NO) levels in lipopolysaccharide (LPS)-stimulated macrophages, consistent with suppression of pro-inflammatory signaling pathways.
Antioxidant mechanisms: Multiple lichen compounds act as free radical scavengers; strong relationships between total phenolic and flavonoid contents and the antioxidant effect of tested extracts have been observed.
Anticancer mechanism: Antiproliferative/cytotoxic effects of atranorin efficiently induced apoptosis and inhibited cell proliferation in various cancer cell lines tested. Similar to usnic acid, atranorin demonstrated strong pro-apoptotic action.
Immunomodulatory mechanism: Polysaccharides (particularly galactomannan from Iceland moss) enhance phagocytosis and stimulate immune cell responses in laboratory models.

5. Scientific Evidence by Area of Use

It is critical to note that the vast majority of scientific research on lichen bioactivity is preclinical. Information related to antioxidant, antimicrobial, anti-inflammatory, anticancer and insecticidal activities of 90 lichen species (from 13 families) and 12 isolated metabolites are reported in the literature. Over 90% of the studies comprised in vitro investigations, such as bioassays evaluating radical scavenging properties, lipid peroxidation inhibition and reducing power, cytotoxicity and antimicrobial bioassays of lichen species and constituents. Human clinical trial data is sparse.

5.1 Antimicrobial Activity

Evidence level: Substantial in vitro; limited clinical data.

UA shows a wide spectrum of biological and pharmaceutical properties, including antibacterial, antiviral, antifungal, antiprotozoal, as well as antitumor activities. The antibacterial activity of UA has been the subject of several studies carried out after the end of the Second World War. However, the interest in the molecule gradually decreased in the 60s, due to the high costs of extraction from lichens, its poor solubility in water, and the development of chemically synthesized antibiotics.

From the 1980s onwards, UA has been the subject of a new wave of research since it could potentially represent an alternative to common antibiotics for the treatment of nosocomial infections linked to antibiotic resistance. Studies carried out over the past thirty years have largely confirmed the efficacy of UA against different strains of bacteria.

Antibacterial activity is one of the most studied bioactivities of lichen dibenzofurans, especially against Staphylococcus aureus. In one in vitro study, extract of Cladonia furcata was the most active antimicrobial agent with minimum inhibitory concentration values ranging from 0.78 to 25 mg/mL. Lichen extracts (methanolic) indicated promising antimicrobial activities against pathogens showing MIC from 62.5 to 500 µg/ml.

For Iceland moss specifically, the minimal inhibitory concentration values against the tested microorganisms ranged from 0.312 to 5 mg/ml. No randomized controlled human trials specifically examining lichens as antimicrobial agents for human infection have been published.

5.2 Antioxidant Activity

Evidence level: Strong in vitro; limited in vivo; no human clinical trials.

Of the lichens tested in one in vitro study, Lecanora atra had the largest free radical scavenging activity (94.7% inhibition), which was greater than the standard antioxidants. The C. islandica methanol extract exhibited moderate free-radical-scavenging activity with IC50 values of 678.38 µg/ml. Moreover, the tested extract had effective reducing power and superoxide anion radical scavenging.

One study reported that concentrations of Cetraria islandica water extract substantially increased the number of antioxidant enzymes (SOD, GPx) in type 1 diabetic children's blood cells and were similar to the standard concentration. This represents one of the very few human (or ex vivo human cell) observations, though it does not constitute a clinical trial with patient outcomes.

Cetraria aculeata, Cetrelia olivetorum, and Cladonia chlorophaea extracts were shown to have significant anti-mutagenic effects in multiple mutagenesis tests. The extracts also improved superoxide dismutase and glutathione peroxidase activities and decreased malondialdehyde and glutathione amounts.

5.3 Anti-inflammatory Activity

Evidence level: Preclinical (in vitro and animal studies); no human clinical trials.

Four compounds isolated from organic extracts of Parmotrema hypoleucinum, Roccella phycopsis, and Xanthoria parietina were identified as atranorin, (+)-iso-usnic acid, methyl orsellinate, and parietin, respectively. The anti-inflammatory effects of lichen extracts and pure compounds were evaluated on RAW 264.7 macrophages cells at different concentrations. At 25 µg/mL all treated samples did not show any effect on cell viability. Atranorin and (+)-iso-usnic acid showed an inhibitory effect on nitric oxide (NO) levels in lipopolysaccharide (LPS)-stimulated macrophages.

Animal studies have used several dosing regimens. Four concentrations (25, 50, 100, and 200 mg/kg) of diffractaic acid from Usnea longissima lichen and five doses (50, 100, 200, 500, and 1000 mg/kg) of Lobaria pulmonaria methanol extracts improved the antioxidant protection mechanism of the tissues and prevented lipid peroxidation in indomethacin-induced mucosal damage models in animals. These are animal-only findings and have not been replicated in human trials.

5.4 Anticancer / Antiproliferative Activity

Evidence level: In vitro only; no human trials.

A study analyzed the potential antiproliferative, antimicrobial, and antioxidative effects of several extracts from lichens (Pseudevernia furfuracea, Lobaria pulmonaria, Cetraria islandica, Evernia prunastri, Stereocaulon tomentosum, Xanthoria elegans and Umbilicaria hirsuta) and their secondary metabolites. The crude extract, as well as the isolated metabolites, showed potent antiproliferative, cytotoxic activity on a broad range of cancer cell lines in 2D (monolayer) and 3D (spheroid) models.

The same authors reported on the sensitivity of up to nine human cancer cell lines (A2780, HeLa, MCF-7, SK-BR-3, HT-29, HCT-116 p53(+/+), HCT-116 p53(−/−), HL-60, and Jurkat) to the antiproliferative/cytotoxic effects of some typical secondary metabolites of lichens (parietin and gyrophoric acid). The analysis of cell-cycle distribution also revealed an accumulation of cells in S-phase.

All extracts were found to have strong anticancer activity toward both the FemX (human melanoma) and LS174 (human colon carcinoma) cell lines with IC₅₀ values ranging from 8.51 to 40.22 µg/mL.

These are entirely in vitro (cell culture) findings. There are no completed human clinical trials evaluating lichen extracts or isolated lichen compounds as cancer treatments.

5.5 Antidiabetic Activity

Evidence level: Preclinical; no human clinical trials.

Salazinic acid from Ramalina celastri, sekikaic acid from R. nervulosa, and usnic acid from R. pacifica showed promising antihyperglycemic effect. Ethyl hematommate, ethyl orsellinate, lecanoric acid, and gyrophoric acid proved to be antidiabetic agents. In another study, atranorin, divaricatic acid, and usnic acid had shown high antidiabetic activity. These findings are from in vitro enzyme-inhibition assays and animal models, not human studies.

5.6 Antiviral Activity

Evidence level: In vitro; no human trials.

Odabasoglu et al. found antiviral activities against three viruses, viz., respiratory syncytial virus (RSV), herpes virus 1, and herpes virus 2 for salazinic acid from Parmelia saxatilis and alectorialic acid from Alectoria nigricans. Polysaccharide fraction compounds, parietin, usnic acid, atranorin, calycin compounds, and rhizocarpic acid are lichen metabolites that have the potential to be used as antivirals. No human antiviral trials have been reported.

5.7 Respiratory and Mucosal Demulcent Effect (Iceland Moss)

Evidence level: Traditional use recognized by the EMA; limited observational human data.

The HMPC concluded that, on the basis of its long-standing use, these Iceland moss preparations can be used as a demulcent (soothing agent) for treating mouth and throat irritation and associated dry cough. This conclusion is based on the category of "traditional herbal medicinal product," meaning although there is insufficient evidence from clinical trials, the effectiveness of these herbal medicines is plausible and there is evidence that they have been used safely in this way for at least 30 years (including at least 15 years in the EU).

Medicinally, its mucilaginous content makes it a valuable remedy for soothing irritation of the respiratory and gastrointestinal mucosa. It has traditionally been used to ease dry throats, relieve dry coughs, support digestion, and provide relief from gastric ulcers and acid reflux.

One post-marketing surveillance study — Mehl and Vestweber (2008), cited in secondary literature — assessed an Icelandic moss pediatric cough syrup and reported good efficacy and excellent tolerance, but this was an observational study without a control arm and is of limited evidentiary value.

5.8 Weight Loss / Metabolic Effects (Usnic Acid)

Evidence level: No clinical trials supporting efficacy; significant safety concerns.

Approximately two decades ago, crude extracts of usnic acid or pure usnic acid were marketed in the United States as dietary supplements for aiding in weight loss as a "fat-burner" and gained popularity in the bodybuilding community; however, hepatotoxicity was documented for some usnic acid-containing products. Recently health food supplements containing usnic acid have been promoted for use in weight reduction, with little scientific support.

5.9 Immunomodulatory Activity

Evidence level: Preclinical; no human clinical trials.

The galactomannan (mean Mr = 18 kDalton) exhibited pronounced enhancement of phagocytosis in both in vitro and in vivo assays. In addition, several polysaccharide fractions, isolated from a hot aqueous extract of Iceland moss by ethanol fractionation and ion-exchange chromatography, exerted significant activity in several immunological assays. These findings remain at the preclinical stage.

6. Body Systems and Health Areas Associated with Lichen

The health benefits of lichen such as anti-oxidation, anti-cancer, anti-microbial, anti-inflammatory, anti-radiation, immune activation, analgesia, anti-thrombosis, anti-obesity, and anti-diabetes have been reported — primarily in preclinical research contexts. The body systems most associated with lichen-derived compounds are:

Respiratory system — demulcent soothing of mucous membranes in throat and airways, particularly via Iceland moss preparations. Recognized under EU traditional herbal medicine frameworks.
Gastrointestinal system — appetite stimulation, mucous membrane soothing, relief of ulcer symptoms; historically documented uses of Iceland moss. Based upon long-standing use, Iceland moss can be used to treat irritation of the mucous membranes in the mouth and throat, and an associated dry, irritating cough; it can also be used to treat temporary loss of appetite.
Immune system — polysaccharide fractions from Iceland moss demonstrated immunostimulatory effects (phagocytosis enhancement) in preclinical models.
Integumentary system (skin) — usnic acid and other compounds have been studied for wound healing, photoprotection, and anti-infective properties in topical applications.
Metabolic system — antidiabetic enzyme inhibition and anti-obesity effects studied in preclinical models.
Cancer biology — multiple lichen compounds demonstrated antiproliferative effects across numerous human cancer cell lines in vitro.
Microbial infections — strong in vitro antimicrobial profiles against Gram-positive bacteria, fungi, and some viruses.

7. Dosage Forms and Dosages Reported in Studies

Dosage data for lichens in human use is extremely limited owing to the near-absence of clinical trials. The following reflect doses reported in published sources:

Iceland moss (traditional/registered herbal use): Herbal medicines containing Iceland moss preparations are usually available as herbal tea to be drunk and in solid or liquid forms to be taken by mouth or applied to the lining of the mouth. Specific doses in the EMA monograph context are not detailed in the publicly available summary.
Diffractaic acid (animal study): Four concentrations (25, 50, 100, and 200 mg/kg) of diffractaic acid from Usnea longissima lichen were studied in animal models.
Lobaria pulmonaria methanol extract (animal study): Five doses (50, 100, 200, 500, and 1000 mg/kg) of Lobaria pulmonaria methanol extracts were tested in animal models.
In vitro anti-inflammatory dosing: Anti-inflammatory effects of lichen extracts and pure compounds were evaluated on RAW 264.7 macrophages cells at different concentrations. At 25 µg/mL all treated samples did not show any effect on cell viability.
In vitro antioxidant (Cetraria islandica): C. islandica methanol extract exhibited moderate free-radical-scavenging activity with IC50 values of 678.38 µg/ml.

No well-characterized, validated human dosing regimens for lichen dietary supplements (outside of registered traditional herbal medicines like Iceland moss throat lozenges) have been established in peer-reviewed clinical literature.

8. Safety Considerations and Interactions

8.1 Hepatotoxicity of Usnic Acid — A Well-Documented Serious Risk

Liver injury, linked to the consumption of products containing usnic acid, was reported in the early 2000s. The severity of the liver injury ranged from mild liver enzyme elevation to more serious cases of hepatitis and/or acute liver failure that required liver transplantation. The US FDA received more than 20 reports of liver toxicity associated with the use of dietary supplements containing usnic acid, leading the FDA to issue a warning in 2001 on one product, namely, LipoKinetix.

LipoKinetix is a multi-ingredient product (containing norephedrine hydrochloride, sodium usniate, 3,5-diiodothyronine, yohimbine hydrochloride, and caffeine) that was marketed as a weight-loss aid and has been associated with several cases of severe hepatotoxicity, including 1 death.

Two patients developed severe hepatotoxicity within 3 months of taking a dietary supplement containing usnic acid. One patient developed fulminant hepatic failure requiring emergency liver transplantation; the other developed submassive hepatic necrosis but did not require transplantation.

A case of a 28-year-old woman who developed acute liver failure and required orthotopic liver transplantation after two weeks of intake of pure usnic acid for weight loss was reported.

Recovery was rapid with stopping the dietary supplement, but some cases were severe and led to acute liver failure and either death or need for emergency liver transplantation.

Usnic acid and Usnea barbata herb were nominated by the National Toxicology Program (NTP) for toxicity evaluations.

The proposed mechanism of hepatotoxicity: usnic acid was introduced as a potential weight loss agent because of its activity in uncoupling oxidative phosphorylation, but which also can cause mitochondrial injury and has been implicated in cases of acute hepatitis which can be severe and has resulted in fatalities, leading to FDA warnings and its withdrawal from the market.

8.2 Additional Adverse Effects of Usnic Acid

Usnic acid was utilized as an antioxidant, anti-proliferative, antimicrobial and antiprotozoal, larvicidal and insecticidal, antifungal, antiviral, algicidal, anti-inflammatory, pain-relieving and antipyretic agent. Many adverse effects were associated with using usnic acid, especially at high dose, including hepatotoxicity, genotoxicity, allergenicity, side effects on the cardiovascular system and adipocytes of fatty tissue.

Some studies have found that usnic acid can cause allergic dermatitis and drug-induced liver injury.

8.3 Heavy Metal and Environmental Contaminant Accumulation

The amounts of Ni, Cr, Zn, Pb, Cu, Fe and Mn in seven lichens growing in Switzerland were determined, including Hypogymnia physodes, Pseudevernia furfuracea, Cladonia rangiferina, Cetraria islandica, Parmelia sulcata, Usnea sp., and Letharia vulpina. It is concluded that some metals within the thalli of Swiss lichens may reach high levels even when these plants are growing in rural and isolated sites. Lichens can accumulate air pollutants easily. Meli et al. reported that arsenic, cadmium, lead, and other toxic elements are present in Cetraria islandica, but stated that the low quantities are not dangerous to human health in samples examined. Wild-harvested lichens from polluted environments may pose higher risk.

8.4 Bitterness, Gastrointestinal Irritation, and Need for Preparation

Food processing techniques reduce the native acerbity and bitterness in lichens and enhance the volatile flavour ingredients to support the development of new food formulations. Many lichens contain secondary metabolites that are irritating if consumed without processing (e.g., soaking, boiling, or drying). High doses of Iceland moss preparations have been associated with nausea, loose stools, and stomach irritation.

8.5 Drug Interactions

The research base on lichen–drug interactions in humans is minimal. The established pharmacological mechanism of usnic acid — inhibition of mitochondrial oxidative phosphorylation — creates a theoretical basis for additive or synergistic toxicity with other hepatotoxic agents or mitochondrial toxins, though this has not been formally characterized in interaction studies. Many studies on the pharmacological activity of usnic acid have focused on how to reduce its toxicity on the basis of rational development and utilization of usnic acid activity.

8.6 Research Limitations and Knowledge Gaps

The toxicology and the mechanism of action of usnic acid need to be examined in detail to the extent of clinical trials. Studies on the metabolism and in vivo process of usnic acid are still insufficient and deserve further study to provide data for its safe use. The research on edible lichens is still lacking. The overall evidentiary base for lichen dietary supplements in humans remains predominantly preclinical, and the gap between in vitro or animal findings and established human clinical outcomes is substantial across all areas of study.

References

Health Conditions

Health conditions that Lichen may help support.

No conditions available.

Body Systems

Body systems that Lichen may help support.

No body systems available.