IngredientsXanthoparmelia (Xanthoparmelia scabrosa) is a type of lichen — an organism made up of fungus and algae living together. More precisely, lichens are formed by a symbiotic association between a mycobiont (fungi) and a photobiont (algae and/or cyanobacteria).
Xanthoparmelia (Parmeliaceae, Ascomycota) is the most species-rich genus of lichen-forming fungi. Species boundaries are based on morphological and chemical features, varying reproductive strategies, and, more recently, molecular sequence data. Xanthoparmelia, with about 800 described species, is the largest genus of lichen-forming fungi, with isidiate Xanthoparmelia species distributed in boreal, temperate, and tropical regions. They commonly occur in semi-arid to arid regions worldwide, especially on siliceous rocks such as granite and sandstone.
The genus has two centres of distribution in Australia and southern Africa; a smaller number of species occur in the Holarctic. The species in this genus characteristically occur on siliceous rocks or soil, predominantly in arid to subarid regions. The genus is characterized by having cell wall polysaccharides of the Xanthoparmelia-type, small ascospores with an arachiform vacuolar body, and the presence of a pored epicortex. It has been hypothesized that the genus diversified in a rapid radiation following a shift towards drier habitats.
The lichenized ascomycete genus Xanthoparmelia includes over 800 described species displaying a considerable range of morphological and chemical variation. Species circumscriptions in this genus have traditionally been based on thallus morphology, medullary chemistry, and the presence or absence of sexual or asexual reproductive structures.
Within dietary supplement commerce, the species almost universally used is Xanthoparmelia scabrosa (Taylor) Hale. The lichen Xanthoparmelia scabrosa (Taylor) Hale (Parmeliaceae) is an ingredient in various aphrodisiac formulations sold on the international market. The NIH Dietary Supplement Label Database (DSLD) documents it under multiple label synonyms, including "Xanthoparmelia," "Xanthoparmelia extract," "Xanthoparmelia scabrosa," "Xanthoparmelia scabrosa extract," and related powder and standardized forms.
Historically, various species of Xanthoparmelia have been used in traditional medicine, particularly in parts of Asia and Africa, where they have been valued for their purported aphrodisiac effects and as remedies for sexual dysfunction. The traditional use of Xanthoparmelia, particularly Xanthoparmelia scabrosa, underscores the longstanding interest in its bioactive properties.
Xanthoparmelia stenophylla is traditionally used in the treatment of sexually transmitted diseases such as syphilis, to reduce inflammation of the gingival tissue, and in the treatment after a snake bite. Moreover, other lichens from the genus Xanthoparmelia with traditional use have been reported as effective in the treatment of arthritis, rheumatism, chronic pain, swelling, and increased menstrual bleeding.
In Mesoamerica and North America, information was obtained on the medicinal use of six lichen species of the genus Xanthoparmelia among the Yuman peoples of northern Mexico and Baja California, where these lichens are employed to treat heart, urinary, and gastrointestinal diseases. Traditional healers described these lichens as having an antihypertensive effect; species such as Xanthoparmelia lineola and X. mexicana, locally known as "stone flower" (wui tabsh), were administered to treat cancer.
Among Navajo peoples of the North American Southwest, Xanthoparmelia chlorochroa (formerly classified as Parmelia molliuscula) was used in paint for leather and as a dye for wool and basketry materials. The "ground lichen" was used by Ramah Navajo weavers to make a warm brown dye. In England, Xanthoparmelia conspersa was reported to yield a red-brown dye for wool.
Lichens broadly have a long history of being used in herbal medicine, and are believed to effectively treat various issues related to skin, respiratory, digestive, obstetric, and gynecological conditions. They are widely used in different types of traditional medicines, including homeopathy, western medical herbals, traditional Indian, and Chinese medicine.
It is important to note that it is difficult to determine the prevalence of lichens in traditional medicine across the world, as most ethnobotanists and ethnographers have historically ignored cryptogams; if the ethnographic literature on a culture does not mention lichens, it might be because the ethnographer did not notice and record the value of lichens. Claims of specific and ancient traditional use of Xanthoparmelia scabrosa for sexual enhancement in particular cultures should therefore be treated with caution in the absence of documented primary ethnobotanical sources.
Lichens produce unique secondary metabolites through various metabolic pathways, and are known to produce more than 1,200 different metabolites that are unique to them and not found in other organisms. Within the genus Xanthoparmelia, secondary metabolite chemistry is both diverse and taxonomically important.
The compound class most closely associated with Xanthoparmelia scabrosa in supplement discussions is the scabrosin esters. The scabrosin esters, isolated from the lichen Xanthoparmelia scabrosa, were reanalysed by modern NMR spectroscopic methods and single-crystal X-ray structural analysis, unambiguously establishing them as a family of epidithiopiperazinedione derivatives. A new scabrosin ester, scabrosin butyrate hexanoate, was also isolated.
Scabrosin esters (SEs), isolated from the lichen Xanthoparmelia scabrosa, belong to the epipolythiodioxopiperazine (ETP) class of secondary metabolites characterized by possession of a reactive disulfide bond. Colony forming assays show that these toxins are active against human tumor cell lines at nanomolar concentrations.
Compounds which contain a dithiopiperazinedione moiety had not previously been identified in lichenized fungi and were found to exhibit potent cytotoxic activity against the murine P815 mastocytoma cell line and the human breast MCF7 carcinoma cell line.
Usnic acid is one of the most frequently tested secondary metabolites of lichens. It is most commonly found in lichens from the genera Usnea and Xanthoparmelia (family Parmeliaceae). This molecule has a dibenzofuranic structure and can naturally exist in two isomeric forms, (+) and (−) enantiomers, depending on the 9b positioned methyl group. Ever since it was first discovered and isolated in 1844, it has attracted research attention due to its various reported effects on human health.
Usnic acid has been claimed to possess numerous therapeutic properties, including antimicrobial, anti-inflammatory, antiviral, anti-proliferative, and antipyretic activities.
A chromatographic method has been developed for the isolation of salazinic, usnic, and stictic acids from lichen samples in a single HPLC run, enabling the quantification of these acids in tested extracts. Phenolic-type compounds such as depsides and depsidones constitute the main secondary metabolites of these species and are also useful as chemotaxonomic markers. Atranorin, (+)-usnic acid, lecanoric acid, diffractaic acid, lobaric acid, stictic acid, and salazinic acid are mostly present in lichen species, and the biological potential of these compounds to counteract oxidative stress has been reported.
For the related species Xanthoparmelia stenophylla, compounds of the depsid structure — lecanoric acid, obtusic acid, and atranorin — as well as usnic acid with a dibenzofuran structure were identified in extracts by HPLC.
In Xanthoparmelia scabrosa specifically, the identified thallus constituents include norlobaridone, norlobariol, loxodin, scabrosin 4,4-diacetate, scabrosin 4-acetate 4-butyrate, scabrosin 4,4-dibutyrate, scabrosin 4-acetate 4-hexanoate, isonorlobaridone, norlobariol methyl ester, conloxodin, conororlobaridone, and usnic acid.
Three key metabolites — salazinic, norstictic, and usnic acids — have been identified and quantified in the related Xanthoparmelia chlorochroa by ultra-performance liquid chromatography/tandem mass spectrometry.
The typical scabrosin ester — acetate butyrate — induces early mitochondrial membrane hyperpolarization assessed by JC-1 staining, accompanied by apoptotic cell death. The toxin lowers ATP in intact cells and inhibits the rate of ATP synthesis in permeabilized cells. Comparison with the effects of the known ATP synthase inhibitor oligomycin B is consistent with ATP synthase being an early target in scabrosin ester-induced cell death.
Other members of the ETP class of toxins, such as gliotoxin, have been shown to induce apoptosis in cells. ETP toxins have been shown to inhibit a variety of enzymes via interaction with sensitive cysteine residues.
The same mechanism that underlies the observed anticancer activity also raises serious safety concerns, as the chemicals found in Xanthoparmelia that might have anti-cancer effects may also be toxic to healthy cells in the body.
A frequently cited marketing mechanism for Xanthoparmelia scabrosa supplements is inhibition of phosphodiesterase type 5 (PDE5). There is limited evidence from in vitro and animal research indicating potential effects on blood flow and smooth muscle relaxation, mechanisms that could theoretically relate to PDE5 pathways. However, it is critical to note that there are no published peer-reviewed clinical trials in humans demonstrating that Xanthoparmelia scabrosa itself acts as a selective PDE5 inhibitor in vivo at supplement doses. This claim derives primarily from marketing claims and from the fact that some supplement products labelled as containing Xanthoparmelia were found to be adulterated with actual pharmaceutical PDE5 inhibitors (see Safety section below).
In studies on the related species Xanthoparmelia stenophylla, acetone extracts showed the highest total phenolic content (167.03 ± 1.12 mg GAE/g) and total flavonoid content (178.84 ± 0.93 mg QE/g), as well as the best antioxidant activity (DPPH IC50 = 81.22 ± 0.54). These are in vitro findings and have not been directly translated to clinical outcomes in humans.
Antimicrobial and antibiofilm tests on Xanthoparmelia stenophylla showed the best activity of hexanic extract, especially against strains of B. cereus, B. subtilis, and S. aureus (MIC < 0.08, and 0.3125 mg/mL, respectively). These are laboratory (in vitro) findings only. The related species Xanthoparmelia pokornyi and its constituents (gyrophoric and stenosporic acid) have been reported to have potential antimicrobial activity.
Xanthoparmelia is used to treat sexual dysfunction, especially erectile dysfunction (ED), as well as to increase sexual desire as an aphrodisiac. People sometimes use xanthoparmelia for cancer, erectile dysfunction, sexual problems that prevent satisfaction during sexual activity, and many other conditions, but there is no good scientific evidence to support these uses. Products containing xanthoparmelia are often marketed for sexual enhancement.
The evidence base for any specific efficacy of Xanthoparmelia scabrosa itself in treating erectile dysfunction is absent from the peer-reviewed clinical literature. No published randomized controlled trials or clinical studies examining the efficacy of the lichen extract against a placebo in human subjects for sexual dysfunction could be identified. The mechanistic rationale remains unproven at the level of human clinical evidence.
Scabrosin esters produced by the lichen Xanthoparmelia scabrosa are active against human tumour cell lines, and the cytotoxicity of some ETPs has made them attractive as potential anticancer agents. Several scabrosins were found to exhibit potent cytotoxic activity against the murine P815 mastocytoma cell line. Colony forming assays show that these toxins are active against human tumor cell lines at nanomolar concentrations.
Evidence strength assessment: All anticancer findings with Xanthoparmelia scabrosa are from in vitro (cell culture) and animal studies. No human clinical trials on cancer treatment with this lichen have been published. The cytotoxic activity that is proposed to underlie anticancer effects is non-selective and is also toxic to healthy cells, a fundamental limitation for therapeutic translation.
Preliminary laboratory studies suggest that extracts of Xanthoparmelia may have antioxidant and antimicrobial properties. These findings are at the in vitro stage. No clinical trials in humans examining Xanthoparmelia scabrosa extract for infectious diseases have been published in the peer-reviewed literature.
The antioxidant activity of isolated compounds and the respective lichen belonging to the Xanthoparmelia genus has been determined using the Oxygen Radical Absorbance Capacity (ORAC) assay; effects as free radical scavengers and on cell survival have been tested in laboratory cell models. These remain exclusively in vitro findings with no corresponding human clinical data establishing antioxidant benefit.
In ethnobotanical documentation of Yuman peoples, six lichens of the genus Xanthoparmelia were reported to be employed to treat heart and urinary tract diseases. This is traditional-use data only. No controlled clinical studies examining Xanthoparmelia in hypertension, heart disease, or related vascular outcomes have been published in peer-reviewed literature.
No standardized or clinically validated dosage for Xanthoparmelia scabrosa exists in the peer-reviewed literature, as no human clinical trials have established dose-response relationships. The following figures reflect only what has been stated in product-related contexts:
Dosage figures appearing on supplement labels and retail sites are not derived from controlled human studies and are therefore not cited here as evidence-based recommendations.
When taken by mouth, xanthoparmelia is possibly unsafe. Xanthoparmelia scabrosa has been marketed as a treatment for erectile dysfunction, but many scientists do not recommend its use. While the lichen contains compounds that may inhibit an enzyme, the same substance can be toxic.
Research on Xanthoparmelia scabrosa has clearly demonstrated toxicity in specific low doses. Industry observers have noted that it makes sense to respond to the science when research demonstrates possible harm or adverse reactions. Xanthoparmelia scabrosa has been researched since 1978, with discoveries on its potent cytotoxic properties first revealed in 1996. The Australian National University's department of chemistry and John Curtin School of Medical Research published articles on the cytotoxic activity of the esters of Xanthoparmelia scabrosa.
The scabrosin esters are the most intensively studied toxic compounds in Xanthoparmelia scabrosa. Scabrosin esters belong to the epipolythiodioxopiperazine (ETP) class of secondary metabolites characterized by possession of a reactive disulfide bond. Colony forming assays show that these toxins are active against human tumor cell lines at nanomolar concentrations. The same nanomolar cytotoxicity applies to normal cells, which is the primary scientific basis for the safety concern regarding oral ingestion.
The lichen metabolite usnic acid (UA) has been promoted as a dietary supplement, and the FDA has received 21 reports of liver toxicity related to the ingestion of dietary supplements that contained UA. This prompted the FDA to issue a warning about one such supplement, LipoKinetix, in 2001.
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. The FDA received numerous reports of liver toxicity associated with the use of dietary supplements containing usnic acid.
Two patients developed severe hepatotoxicity within 3 months of taking a dietary supplement containing usnic acid. One developed fulminant hepatic failure requiring emergency liver transplantation; the other developed submassive hepatic necrosis but did not require transplantation. Thorough investigation, including histopathological examination of the liver, revealed no other cause of acute liver injury.
Recovery was rapid upon stopping the dietary supplement, but some cases were severe and led to acute liver failure and either death or need for emergency liver transplantation. Instances of acute hepatitis have also been reported with other multi-ingredient dietary supplements that contain usnic acid.
Usnic acid and Usnea barbata herb were nominated by the National Toxicology Program (NTP) for toxicity evaluations.
Toxicity following ingestion of the vagrant, foliose lichen Xanthoparmelia chlorochroa was identified as the putative etiology in the death of an estimated 400–500 elk on the Red Rim-Daley Wildlife Habitat Management Area in Wyoming during the winter of 2004. A report in 1939 attributed toxicity of X. chlorochroa in cattle and sheep to usnic acid. Clinical signs in symptomatic ewes dosed with (+)-usnic acid included lethargy, anorexia, and signs indicative of abdominal discomfort. Serum creatine kinase, aspartate aminotransferase, and lactate dehydrogenase activities were considerably elevated. Only symptomatic ewes exhibited appreciable postmortem lesions consisting of severe degenerative appendicular skeletal myopathy.
Xanthoparmelia scabrosa actively accumulates copper, lead, sulfur, and zinc from its substrate. In urban areas, levels of these anthropogenic elements rise sharply. This property — well-established in the environmental monitoring literature — means that the geographic origin and collection conditions of raw lichen material used in supplements are directly relevant to the heavy metal safety profile of any finished product.
In 2004, the US Food and Drug Administration (FDA) seized numerous brand-name supplement products containing xanthoparmelia because these products also contained the prescription drug tadalafil (Cialis), used to treat erectile dysfunction.
A product called Stamina-Rx and Stamina Rx for Women also drew regulator attention when, in 2003, it was found to contain the prescription drug ingredient tadalafil. The FDA has also cited the presence of benzamidenafil — a pharmaceutical in the same therapeutic class as the PDE5 inhibitors sildenafil, tadalafil, and vardenafil — in products marketed alongside xanthoparmelia claims.
These regulatory actions are significant because they demonstrate that observed "effects" in consumers of xanthoparmelia-containing sexual enhancement supplements may have been attributable to undisclosed pharmaceutical adulteration rather than to the lichen itself.
As of the date of this article, no published randomized controlled trials, phase I/II/III clinical studies, or prospective cohort studies examining safety or efficacy of oral Xanthoparmelia scabrosa extract in human subjects have been identified in peer-reviewed databases. The totality of evidence for both benefit and harm at the human level is thus based on case reports, regulatory findings, in vitro studies, and animal toxicology.
Health conditions that Xanthoparmelia may help support.
Body systems that Xanthoparmelia may help support.
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