Marsh tea

Marsh Tea (Rhododendron tomentosum / Ledum palustre): A Comprehensive Reference

1. Identity and Botanical Classification

Rhododendron tomentosum Harmaja (previously Ledum palustre) is a fragrant evergreen shrub found in peaty soils in northern Europe, Asia, and North America, commonly referred to as wild rosemary, marsh tea, marsh rosemary, or northern Labrador tea. The name "marsh tea" is in most widespread use in the European English-language tradition, while "northern Labrador tea" is the dominant common name in Canada.

The former Latin name Ledum palustre derives probably from the Latin word laedere — "hurt," which may refer to its intensive fragrance capable of causing a headache, and from palus — "bog," in connection with its boggy habitat. The Greek word ledos, meaning "robe" or "wool," provides an alternative etymology, relatable to the dense hairiness of the herb.

Rhododendron tomentosum (syn. Ledum palustre), commonly known as marsh Labrador tea, northern Labrador tea, marsh rosemary, or wild rosemary, is a flowering plant in the subsection Ledum of the large genus Rhododendron in the family Ericaceae. As Ledum palustre, it was integrated into school medicine by Linnaeus in 1775.

The plant was formerly known by its scientific name Ledum palustre but is now accepted under the botanical name Rhododendron tomentosum, belonging to the plant family Ericaceae. The name change was formally accepted after 1990. Additional synonyms in the literature include Rhododendron palustre and Ledum palustre var. decumbens.

1.1 Morphology and Natural Habitat

Rhododendron tomentosum is a low-growing shrub, typically 50 to 120 centimetres tall. Its evergreen leaves are slender, measuring 12–50 millimetres long and 2–12 millimetres wide. The underside of its leaves bears a dense, rusty, wool-like fuzz — a distinguishing feature. The plant produces small, white, five-lobed flowers arranged in clusters, forming a corymb about 3–5 centimetres in diameter.

Rhododendron tomentosum thrives in northern latitudes, inhabiting diverse environments such as peaty soils, shrubby areas, moss and lichen tundras, and sphagnum marshes. The species can be found on wetlands in northern and central Europe, Asia, and North America. In some locations, for example in Poland, it is considered an endangered species, mainly due to the degradation and dewatering of its natural habitats.

R. tomentosum, formerly Ledum palustre, is an aromatic plant belonging to the Ericaceae family. It is widely spread in boreal forests, mires, and damp heaths of the Northern Hemisphere, such as Scandinavia, Ireland, and Canada.

1.2 Common Names and Synonymy

The plant is commonly referred to as Marsh Labrador Tea, Wild Rosemary, Northern Labrador Tea, Marsh Cistus, and sometimes simply as Labrador Tea. In German it is known as Sumpfporst, and in French as lédon des marais. Other historical names include Swamp Tea, James' Tea, and Moth Herb.

Note on related species: Labrador tea is a name for the dried leaves of Rhododendron groenlandicum, R. tomentosum, or R. neoglandulosum (family Ericaceae, previously genus Ledum), as well as for the beverage native to North America which is made from them. These three species have overlapping traditional uses, but differ chemically; this article focuses primarily on R. tomentosum (marsh tea / wild rosemary) as the species classically known in European medicine under the name "marsh tea."

1.3 Commercially Available Forms and Preparations

Marsh tea has historically been prepared as a herbal infusion (tisane), a decoction, a tincture or alcohol extract, and a distilled essential oil. The dried aerial parts — principally the shoots and leaves — are the primary material used across all these forms. The common recipe for making Labrador tea is to add one teaspoonful of dried leaves to one cup of boiling water and to brew for 5 minutes. It is often sweetened or enriched with other flavours. The plant is also available as an essential oil obtained by hydrodistillation, as a supercritical CO₂ extract, and, in homeopathic practice, in ultra-dilute centesimal potencies (notably Ledum palustre 30c and higher). Dried leaves are additionally used to spice meat, soups, sauces, salads, beer, cakes, and other dishes.

2. Traditional and Historical Use

2.1 General Ethnomedicinal Context

At least since the eighteenth century, the plant has been used in ethnomedicine for the treatment of various ailments, such as rheumatism, cough, cold, and insect bites, as well as a repellent. However, its use almost certainly pre-dates systematic documentation. It has been used for centuries in folk medicine to treat rheumatic diseases, lung problems, and infections, as well as for its repellent properties.

2.2 Northern European Tradition (Scandinavia, Germany, Baltic Region)

In Scandinavia and the Baltic states, marsh tea occupied a central place in domestic folk medicine. In Lithuania, the plant is used for healing rheumatism, different pains, insect bites, eczema and other skin problems, infections, bronchitis, asthma, cold, and tuberculosis, and to block bleeding, among other purposes.

The leaves were thought to be narcotic and diaphoretic, and were employed in dysentery and in various cutaneous affections, particularly leprosy and scabies. In complaints of the skin, they were used both internally and externally, in the form of a decoction.

The plant's strong scent was employed deliberately as an insect deterrent. Its strong fragrance led to its use as a natural insect repellent in Scandinavia and Eastern Europe. In Germany it was known as Mottenkraut (moth herb) and Wanzenkraut (bug herb), reflecting its use for repelling clothes moths and bedbugs. In Germany it was sometimes substituted for hops in the preparation of beer.

2.3 North American Indigenous Tradition

R. tomentosum ssp. subarcticum, formerly Ledum palustre ssp. decumbens, was one of the most commonly used medicinal plants by Canadian First Nations. The plant, known as Northern Labrador Tea, was applied among multiple Cree and Inuit populations in cold and flu symptoms, cough, sore throat, shallow breathing, tuberculosis, headache, toothache, stomach ache, snow blindness, diarrhea, wounds, back and kidney pain, rheumatism, arthritis, infections, inflammation, heart and chest pain, fainting and weakness, swollen limbs, foot sores, and hangovers.

Externally, crushed or powdered leaves were used on burns, either directly or mixed with grease. Decoctions of the plants were also used to wash burns and on dry, itchy, or chapped skin and on sores. More latterly, alcohol extracts of the leaves have been used to treat infestations and fungal skin diseases.

Notably, Inupiat people considered Marsh Labrador tea, R. tomentosum, a poisonous plant, indicating a degree of cultural recognition of its toxicity at higher doses.

2.4 Medieval Brewing: Gruit

Marsh Labrador tea has traditionally been used as a gruit in brewing beer in the Middle Ages. The gruit system was the pre-hop method of bittering and preserving ale across northern and central Europe. The main herbal ingredient of gruit was bog myrtle (Myrica gale). In areas where bog myrtle did not grow, marsh rosemary (Ledum palustre) would be used instead. In western Germany the name gagel had also been used for marsh rosemary, and in Germany and Scandinavia the name pors had been used for bog myrtle, making identification historically confusing. The two plants grow mutually exclusive, with marsh rosemary's habitat being circumpolar; thus, western Germany and the Netherlands tended to use bog myrtle in the gruit, and further northeast marsh rosemary was used.

2.5 Linnaeus and Early Scientific Documentation

R. tomentosum as Ledum palustre was integrated into school medicine by Linnaeus in 1775. Nineteenth-century eclectic botanical texts confirm that the plant was officially recognised as a medicinal agent in European pharmacy, and the related Ledum groenlandicum, or Labrador tea, a larger plant native to North America growing in damp places in Canada and the northern United States, had leaves with an agreeable odour and taste that were esteemed pectoral and tonic.

3. Key Chemical Constituents

3.1 Essential Oil (Volatile Fraction)

The essential oil is the most pharmacologically studied fraction of the plant. Most literature on the chemistry of R. tomentosum concerns the essential oil, regarded as the most important from the pharmacological point of view. The composition of the essential oil varies considerably with habitat as well as age and part of the herb. The content of the essential oil depends strongly on the vegetation phase. Ninety compounds have been identified in one recent analysis, accounting for almost 98% of the essential oil.

In total, up to 70 compounds were identified by GC-MS and GC in studies of Lithuanian plants; sesquiterpene hydrocarbons (54.1–76.1%) were found to be the main fraction. The major compounds were palustrol (24.6–33.5%) and ledol (18.0–29.0%). Ascaridol isomers (7.0–14.0% in three oils), myrcene (7.2% and 10.1%), lepalol (3.3% and 7.9%), and cyclocolorenone isomers (4.1%) were determined as the third major constituents.

Palustrol and ledol were the first or second dominant compound in all the oil samples studied; the total average quantity of these two sesquiterpene alcohols comprised on average 42.6–62.5% of all the oil content.

The volatile fraction of R. tomentosum is chemically variable and chemotypes of the plants need to be defined if the oil is to be used for therapeutic purposes. Cluster analysis of literature data has enabled researchers to define at least 10 chemotypes of the plant.

The seed oil has a somewhat distinct composition from shoot oil. Seeds and shoots of the same plant have different quantities of palustrol and ledol. Plant seeds contain more palustrol (38.3%) and less ledol (27.0%), in contrast to shoots, where the ledol quantity (36.5%) predominates over palustrol (21.0%).

Other notable components of the essential oil include the monoterpene hydrocarbons p-cymene, myrcene, and limonene; the bicyclic monoterpenoid ascaridole; and minor sesquiterpenes including cyclocolorenone and lepalol. Among the compounds reported in essential oils of L. palustre are sabinene, β-myrcene, p-cymene, limonene, α-thujenal, γ-terpineol, bornyl acetate, ascaridole, palustrol, and ledol.

3.2 Non-Volatile Phenolic Compounds

Other substances in R. tomentosum extracts include pentacyclic triterpenoids (uvaol, uvaol acetate, ursolic acid, ursolic acid acetate, lupeol, α-amyrin, taraxerol, and others) and low-molecular-weight polyphenols, most of which are flavonoids (quercetin, hyperoside, catechin, epicatechin, and others) and coumarins (scopoletin, esculetin, fraxetin, fraxidin, and others).

Diethyl ether extracts of the plant exhibit higher total polyphenol and flavonoid content as well as stronger antioxidant capacity. HPLC analysis confirmed the presence of key polyphenolic substances, including neochlorogenic acid, chlorogenic acid, hyperoside, isoquercitrin, quercitrin, and avicularin.

The phytochemical analysis of the plant has shown the presence of flavonols (11 compounds), catechins (5), and hydroxycinnamic acids represented by caffeic, ferulic, and chlorogenic acids. Also found are the phenolic glycoside arbutin, coumarins — coumarin, umbelliferone, scopoletin, esculetin and esculin — and tannins, including methyl gallate and pyrogallol.

A 2025 metabolomics-based study identified phenolic acids, coumarins, sugars, terpenes, stilbenes, flavonoids, procyanidins, and fatty acids as molecular classes of interest. Phenolic acids and flavonoids were the most represented classes.

The flavonoid fraction is dominated by flavonol glycosides. R. tomentosum's flavonoids are mainly composed of flavonol glycosides, namely quercitrin, isoquercitrin, hyperoside, rutin, and related methylated and phenolic derivatives.

The glucoside ericolin (C₃₄H₅₆O₂₁) has also been extracted. This glucoside, on heating with diluted sulphuric acid, decomposes into sugar and ericinol (C₁₀H₁₆O), a colourless, peculiar-smelling oil which turns brown in air upon oxidation.

4. Scientific Evidence by Area of Use

4.1 Anti-inflammatory and Analgesic Activity

Evidence level: In vitro and in vivo (animal); no controlled human clinical trials.

Anti-inflammatory activity of R. tomentosum extract was studied in vitro, verifying the traditional use of this herb as a painkiller. Moderate inhibition of prostaglandin biosynthesis and PAF-induced exocytosis was obtained. It was suggested that large amounts of phenolic compounds, such as quercetin derivatives, as well as the essential oil, are responsible for this result.

Anti-inflammatory activity of Lithuanian marsh rosemary essential oils has been demonstrated by subcutaneous carrageenan injection-induced hind paw oedema tests. In these animal model studies, results showed that L. palustre essential oil produced a significant inhibition of oedema (50–73%) for hydrodistillation (HD) oil and (52–80%) for supercritical fluid extraction (SFE) oil. These results were similar to those obtained with piroxicam (70%) and ketoprofen (55%). These are animal data and cannot be directly extrapolated to humans.

In the context of rheumatoid arthritis, Rhododendron tomentosum is an aromatic plant traditionally used for alleviating rheumatic complaints, which makes it a potential candidate for a natural drug in rheumatoid arthritis (RA) treatment. However, the effects of the plant's volatiles on apoptosis of synovial fibroblasts and infiltrating leucocytes of RA synovia had not been reported prior to recent work. The volatile fraction of R. tomentosum is chemically variable, and chemotypes of the plants need to be defined if the oil is to be used for therapeutic purposes.

Cluster analysis of literature data enabled researchers to define 10 chemotypes of the plant. The volatile fractions were then tested for bioactivity using RA-specific in vitro models. Essential oils of two wild types (γ-terpineol and palustrol/ledol type) and one in vitro chemotype (ledene oxide type) were obtained by hydrodistillation and their bioactivity was tested in two in vitro models: (I) peripheral blood lymphocytes of healthy volunteers and (II) synoviocytes and immune cells isolated from synovia of RA patients. These were cell culture studies; no controlled clinical trials in RA patients exist.

In vivo studies with rodents showed that the infusion of this plant can enhance the activity of antituberculous drugs.

4.2 Antimicrobial Activity

Evidence level: In vitro; no human clinical trials.

The essential oil of wild rosemary with its rich polyphenolic fraction possesses analgesic, anti-inflammatory, antimicrobial, antiviral, antifungal, and insecticidal potential, demonstrated by in vivo and in vitro studies.

Antifungal activity has been specifically investigated. Antifungal activity of R. tomentosum essential oils was evaluated by several different techniques: against Penicillium cyclopium, Trichoderma harzianum, and Candida parapsilosis using an agar diffusion method, and amperometrically using Saccharomyces cerevisiae yeast-modified electrodes.

Two novel flavonoid glycoside compounds isolated from Ledum palustre showed in vitro antifungal activity against Cryptococcus neoformans, Saccharomyces cerevisiae, Aspergillus niger, and Candida albicans, as well as cytotoxicity against KB cells. All of these findings are from laboratory models; their clinical significance in humans is unknown.

A 2024 study examined the polyphenol and flavonoid content of R. tomentosum extracts alongside their antioxidant and antimicrobial activity. The study confirmed the identity of key polyphenolics including rutin, hyperoside, quercetin, and chlorogenic acid as important contributors to the observed bioactivity.

4.3 Antioxidant Activity

Evidence level: In vitro; no human clinical trials.

Radical scavenging activity of R. tomentosum essential oils depended on the plant's vegetation stage. The highest activities were obtained for essential oils isolated from young shoots collected in June. Standard assays (ABTS, DPPH, TROLOX equivalents) have been used across multiple studies to quantify this antioxidant capacity.

Research results demonstrate that the timing of harvest of R. tomentosum impacts the plant's phenolic content and its antioxidant and anti-inflammatory activities. This seasonal variability has important implications for standardisation of any therapeutic preparation.

4.4 Insect Repellent and Insecticidal Activity

Evidence level: In vitro and controlled laboratory assays; limited field data.

Volatile components of R. tomentosum have been found to possess repellent properties effective against bedbugs and clothing moths. The plant synthesises a high content of terpenoids in glandular trichomes and emits a strong characteristic smell, which attracts bees and other pollinating insects.

A study of an ascaridole-rich chemotype of essential oil from Polish plants demonstrated insecticidal activity against mosquitoes, moths, and flies. GC-MS analysis evidenced an uncommon chemotype characterised by ascaridole (35.3% as sum of cis-ascaridole and isoascaridole) and p-cymene (25.5%) in that population. The sesquiterpene alcohols palustrol and ledol are considered the primary contributors to repellent properties based on available laboratory evidence.

4.5 Postoperative Ecchymosis and Edema (Human Preliminary Data)

Evidence level: Preliminary; single-arm observational study; combination product; no placebo comparison group.

A notable clinical study examined the use of a topical product containing both Arnica montana and Rhododendron tomentosum (Ledum palustre). Each patient used topical hydrogel pads containing Arnica 50M and Ledum 50M. The pads were applied bilaterally after surgery through postoperative day 6. At each postoperative visit, patients were evaluated by their respective surgeons and assigned a subjective physician-patient rating score comparing each patient's observed healing compared with expected healing. The preliminary results from this study demonstrated that the combination of topical Arnica montana and Rhododendron tomentosum (Ledum palustre) may be effective in reducing postoperative ecchymosis and edema after oculofacial surgery. This study used homeopathic dilutions (50M), lacked a concurrent randomised placebo arm, and did not isolate the contribution of R. tomentosum from Arnica. Results should therefore be considered very preliminary.

4.6 Injection-Site Pain: A Double-Blind Randomised Controlled Trial

Evidence level: Preliminary RCT; early termination; homeopathic preparation; limited generalisability.

A trial of Ledum palustre 200cH significantly outperformed placebo in resolving pain and discomfort in injection sites sooner after COVID-19 vaccination. This product, also known as wild rosemary or northern Labrador tea (Rhododendron tomentosum), has been used in ethnomedicine to treat a variety of illnesses including insect stings, rheumatism, coughs, and colds. The trial was a double-blind, randomised, placebo-controlled design published in 2025; however, it used a homeopathic ultra-dilution preparation (200cH), and the trial ended early with fewer participants than intended. The relevance of homeopathic preparations to the pharmacological profile of the whole plant extract or essential oil is scientifically contested.

4.7 Antidiabetic and Metabolic Activity

Evidence level: Preliminary; in vitro and animal models only.

Recent scientific research has reported promising antidiabetic, antioxidant, and anticancer properties. These findings are primarily from cell culture and animal model studies. No human clinical trials of marsh tea specifically for glycaemic control have been identified in the peer-reviewed literature. The mechanisms proposed involve inhibition of α-glucosidase and modulation of oxidative stress pathways, attributable to the plant's flavonoid fraction. In vivo studies with rodents showed that the infusion of this plant can enhance the activity of antituberculous drugs.

4.8 Anticancer Activity

Evidence level: Preliminary; in vitro only.

Modern studies on R. tomentosum demonstrated that extracts of the plant exhibit anti-inflammatory, analgesic, antimicrobial, antifungal, antiviral, anticancer, antidiabetic, and antioxidant properties. However, the anticancer findings are at the level of cell-line cytotoxicity assays. Novel flavonoid glycoside compounds isolated from Ledum palustre showed cytotoxicity against KB cells in vitro. No clinical trials addressing oncological outcomes have been identified. These preliminary findings should not be interpreted as evidence for clinical anticancer efficacy.

4.9 Overall Assessment of the Evidence Base

The overall evidentiary profile for marsh tea as a medicinal preparation is characterised by a wide range of well-characterised phytochemistry and promising preclinical (in vitro and animal) data. Rhododendron tomentosum is used in herbalism to make a herbal tea called "Labrador tea." However, no material benefit has been documented in any properly controlled study. This statement reflects the position as of early 2026. The preponderance of evidence remains at the in vitro and animal model level, with only one small early-terminated RCT (using a homeopathic dilution) providing any placebo-controlled human data.

5. Body Systems and Health Areas of Association

• Musculoskeletal system: Used traditionally for rheumatism; in vitro and animal evidence suggests anti-inflammatory mechanisms relevant to joint disease.
• Respiratory system: Used traditionally for the treatment of asthma, infections of the respiratory tract, cough, whooping cough, bronchitis, and chest ailments; historically esteemed as an expectorant and diaphoretic.
• Integumentary (skin) system: Employed in various cutaneous affections, including leprosy and scabies; used both internally and externally in the form of a decoction in skin complaints.
• Gastrointestinal system: Traditional use for gastrointestinal disorders; the plant has tonic properties and has been used for dysentery.
• Immune/Infectious disease: Antimicrobial and antiviral activities demonstrated in vitro; used traditionally for colds, flu, and infections.
• Central nervous system (historically, with caution): Historically noted as narcotic and diaphoretic; ledol's CNS effects (stimulant at low doses, depressant/toxic at higher doses) have been documented.
• Metabolic: Preliminary antidiabetic and antioxidant activity identified in laboratory studies.
• Reproductive (abortifacient — historical, toxic context): The essential oil of Ledum palustre is a potent irritant of the gastrointestinal tract, kidneys, and urinary tract; other toxic effects include abortion. This must be understood in the context of toxicity, not therapeutic use.

6. Dosage Forms and Reported Dosages

Because no formal pharmacopoeial monograph from the European Pharmacopoeia, ESCOP, or WHO has been identified for marsh tea in the available sources, and because no established therapeutic dose has been validated through controlled clinical trials, the dosage information below reflects only what has been reported in primary sources.

• Herbal infusion (tisane): The common recipe for making Labrador tea is to add one teaspoonful of dried leaves to one cup of boiling water and to brew for 5 minutes. It is often sweetened or enriched with other flavours. Labrador tea is a valuable source of ascorbic acid, with tonic, improving digestion and relaxing activity. However, this beverage should not be drunk more than once daily because of the ledol and grayanotoxin toxicity.
• Essential oil (preclinical anti-inflammatory study): In the animal model study, L. palustre essential oil produced a significant inhibition of oedema of 50–73% for hydrodistillation oil and 52–80% for supercritical CO₂ oil. Specific dosages used in this animal experiment are not reproduced here, as they were not reported in the available source abstract.
• Homeopathic preparation: Used in ultra-dilute centesimal potencies (30c, 200cH, and 1M) in homeopathic practice; the RCT referenced above used the 200cH potency. It is used in ultra-diluted form in homeopathy for various purposes.
• Topical product (clinical study): Each patient used topical hydrogel pads containing Arnica 50M and Ledum 50M, applied bilaterally after surgery through postoperative day 6.
• Critical note: The absence of clinical evidence means that there are no data available regarding the safe dosage of R. tomentosum.

7. Safety Considerations and Interactions

7.1 Ledol Toxicity

R. tomentosum is regarded as a poisonous plant due to the content of toxic volatile compounds, especially the sesquiterpenoid ledol, in its essential oil. Although a low concentration of ledol in the beverage may have a restorative effect similar to caffeine, large doses can affect the central nervous system. Initially, psychomotor stimulation occurs; afterwards, seizures and cramps; and eventually paralysis, breathing problems, and even death.

Ledol can affect the central nervous system, initially leading to psychomotor stimulation, then to seizures and cramps, and finally to paralysis, breathing problems, and even death. Moreover, it was reported to increase blood pressure — for this reason, plant material containing the minimal amount of ledol was recommended.

First symptoms of overdose are dizziness and disturbances in movement, followed by spasms, nausea, and unconsciousness.

7.2 Grayanotoxin Toxicity

The literature shows that another major toxic compound found in Rhododendron species leaves is grayanotoxin I. It is a cyclic diterpene with biological activity similar to the Veratrum alkaloids. Many rhododendrons and other members of the family Ericaceae contain grayanotoxins, including some of the Labrador tea species. Poisoning from grayanotoxins is rarely fatal in humans but in concentration can cause hallucinogenic effects.

The essential oil of Ledum palustre (marsh Labrador tea), which contains flavones, monoterpenoids, and sesquiterpenoids, is a potent irritant of the gastrointestinal tract, kidneys, and urinary tract; other toxic effects include abortion.

7.3 Comparative Toxicity Across Related Species

R. groenlandicum is regarded as less toxic than R. tomentosum because of the minimal ledol quantity in its essential oil composition. This distinction is important for consumers and practitioners, since products labelled "Labrador tea" may derive from any of several related species with differing toxic profiles.

7.4 In Vitro Toxicity Data

A toxicity test employing brine shrimp (Artemia sp.) larvae and eight essential oil samples revealed that all R. tomentosum essential oils under study were notably toxic. LC₅₀ and LC₉₅ values were in the range 11.23–20.50 and 34.00–76.07 µg/mL, respectively. Essential oils obtained from shoots gathered in September (seed-ripening stage), containing appreciable amounts of palustrol (26.0%), ledol (21.5%), and ascaridol (7.0%), appeared to be the most toxic.

7.5 Abortifacient Properties

Multiple sources note abortifacient properties linked to the plant's irritant effects on smooth muscle. The essential oil of Ledum palustre has toxic effects including abortion. This property has historically been the basis for deliberate misuse and represents a significant clinical concern.

7.6 Reproductive Toxicity and Use in Pregnancy

Given the documented abortifacient and uterotonic properties of the essential oil, use of marsh tea preparations in pregnancy is contraindicated on the basis of available toxicological evidence.

7.7 Chemotype Variability as a Safety Issue

The volatile fraction of R. tomentosum is chemically variable, and chemotypes of the plants need to be defined if the oil is to be used for therapeutic purposes. This means that a single commercial preparation labelled "marsh tea essential oil" may have a substantially different chemical composition — and therefore different toxicological profile — depending on the geographic origin and harvest season of the raw material.

7.8 Drug Interactions

No formally studied pharmacokinetic drug interactions with R. tomentosum preparations in humans have been identified in the peer-reviewed sources reviewed. An in vivo study was performed on the pharmacokinetics of aesculin, aesculetin, fraxetin, fraxin, and polydatin in canine plasma. The pharmacokinetic analysis revealed varying plasma concentrations, absorption rates, and metabolic fates of the identified coumarin derivatives, following the oral administration of R. tomentosum extract. The coumarin derivatives present in marsh tea (scopoletin, esculetin, fraxetin) have theoretical potential for interactions with anticoagulant medications, but this has not been studied in humans.

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