IngredientsThe pepper bark tree is formally known as Warburgia salutaris (Bertol. f.) Chiov., belonging to the family Canellaceae, and it holds significant cultural, medicinal, and economic value in southern Africa. The specific epithet salutaris is Latin, meaning "healthful," a direct reference to its medicinal properties. The common name "pepper-bark tree" relates to the pungent inner bark that tastes peppery.
The genus Warburgia Engl. is a member of Canellaceae Martius, a dicot family that contains 16 species grouped in 6 genera. The genus Warburgia comprises four species, all confined to Africa, with only one (W. salutaris) occurring in South Africa. The genus was named after Dr. Otto Warburg (1859–1938), a German-Jewish botanist. Warburgia species are characterized by aromatic and pungent bark. Warburgia salutaris, W. stuhlmannii, and W. ugandensis have yielded a series of drimane sesquiterpenoids including isopolygodial, muzigadial, polygodial, salutarisolide, ugandensidial, and warburganal.
Note on naming: The term "Pepper Bark Tree" is also historically applied to Drimys winteri (Winter's Bark), a South American species in the unrelated family Winteraceae. These two plants share a common name due to similar organoleptic properties of their bark but are botanically distinct and belong to different continents and families. This article focuses principally on Warburgia salutaris, as it is the species most consistently identified in the peer-reviewed and ethnobotanical literature under the name "Pepper Bark Tree," while also covering the history of Drimys winteri where relevant.
Warburgia salutaris is a medium-sized, evergreen, aromatic tree growing to a height of 10–20 m. The bark of W. salutaris is rough, mottled, and has yellowish corky lenticels on older branches, while the inner bark is reddish. Leaves of W. salutaris are alternately arranged, densely gland-dotted, oblong, glossy green above, and a paler green with a prominent rachis below, with smooth leaf margins. Flowers are either solitary or occur in three-flowered cymes produced in the axils of leaves, followed by oval, green to yellowish berries 20–40 mm in diameter, turning purple when mature and covered in glands, containing several seeds inside the fruits.
This slow-growing species is part of an early diverging group of basal angiosperms, thought to be native to eastern and southern Africa. However, subsequent studies confined the distribution of W. salutaris to a sub-region of southern Africa, specifically South Africa, Eswatini (previously known as Swaziland), Zimbabwe, Malawi, and Mozambique. Within South Africa, it extends southwards as far as north-eastern KwaZulu-Natal, Mpumalanga, and Limpopo, also occurring in Swaziland, Zimbabwe, and Malawi. Its habitat is variable, found growing in coastal, riverine, dune, and montane forest as well as open woodland, thickets, and kloofs.
W. salutaris is utilized as both dried and fresh material, and while stem bark is the most widely used part, the leaves and roots of the tree are also harvested. Warburgia salutaris is commercially available in crude form, as an essential oil, and in other dosage forms in over-the-counter products. In traditional contexts, preparations include bark decoctions, powdered bark applied as snuff or mixed into ointments, smoked bark, and leaf preparations. Some communities use the bitter, peppery, aromatic leaves of the pepper bark to flavour food and to make tea. A resin can be extracted from the bark, which is also a source of tannins.
In the South American context, the term "pepper bark tree" has been applied to Drimys winteri, a species in the unrelated family Winteraceae. Drimys winteri, also known as Winter's Bark, foye, and canelo, is a slender species of tree growing up to 20 m tall, native to the Magellanic and Valdivian temperate forests of Chile and Argentina, where it is a dominant tree in the coastal evergreen forests. The genus name Drimys derives from the Greek word drimys, meaning "pungent" or "sharp," in reference to the acrid taste of the bark.
Drimys winteri was first documented by Europeans during Sir Francis Drake's circumnavigation of the globe in 1577–1580, when Captain John Winter encountered the tree in the Strait of Magellan in 1578 and recognized its medicinal potential. In 1776, the German botanists George and Johann Reinhold Forster assigned it the scientific name Drimys winteri, reporting it as a medicinal plant used against scurvy and recommending it instead of Jesuit's Bark (Cinchona officinalis). The bark is gray, thick, and soft, and is used as a pepper replacement in Argentina and Chile. The peppery compound in canelo is polygodial. The species is sacred to the Mapuche people of southern Chile and Argentina, who gather under their canopies to celebrate their assemblies and rites.
Warburgia salutaris (the pepper bark tree) is one of the most highly valued medicinal plant species worldwide. Native to southern Africa, this species has been extensively harvested for the bark, which is widely used in traditional health practices. Indigenous communities have long revered this tree for its myriad of traditional uses in treating various ailments, including conditions such as abdominal pain, respiratory tract infections, malaria, febrile complaints, candidiasis, headache, tuberculosis, sexually transmitted diseases, sinus conditions, and rheumatism.
The tree is widely used in the region and is linked to the local traditional medicine practices of various cultural groups including the Zulu, Sotho, Tsonga, and Venda in South Africa, and the Shona, Changana, and Siswati ethnic groups in Zimbabwe, Mozambique, and Eswatini respectively. Forty-three ethnomedicinal use records have been collected for W. salutaris in Southern Africa, referring to a variety of preparations used for topical and internal administration.
Ethnomedicinal uses of Warburgia species have been recorded from east, central, and southern Africa for 30 human and 7 animal ailments. Warburgia species are used to treat gastro-intestinal disorders, cold, cough, and sore throat; fever or malaria, as well as respiratory and odontological ailments.
The bark of Warburgia salutaris is used in traditional medicine as an expectorant and smoked for coughs and colds, including a topical application for sores and inflammation. The bark is the most-used part for oral or topical preparations. Often combined with other herbs, it is powdered as a snuff for headache relief, smoked to relieve coughs, and prepared to make an anti-inflammatory ointment for sexually transmitted infections and urogenital inflammation. For example, W. salutaris mixed with fat, and sometimes in conjunction with the leaves and stalks of Hibiscus surattensis, is applied topically to treat genital sores and inflammation. The bark is also used in combination with Artemisia afra (leaves) and the roots of Acorus calamus as an anti-infective agent. The bark powder of W. salutaris and Erythrophleum lasianthum is combined as a snuff to treat headaches.
It is commonly harvested from the wild and widely sold in local markets for medicinal purposes. Medicinally, the pepper-like, bitter stems and root bark are used to cure many ailments in traditional medicine including cough, cold, bronchial infections, oral thrush, and cystitis, among other ailments. Taken orally, bark preparations are believed to cure spots in the lungs.
Warburgia salutaris is one of the most highly valued medicinal plant species in southern Africa. Due to its popularity in folk medicine, it is overexploited in many regions and is deemed threatened throughout its range. Stratified random, semi-structured interviews conducted across southern Mozambique (182 interviews, complemented by 17 focus group discussions) found that W. salutaris was used medicinally to treat 12 health concerns, with bark being the most commonly used part.
Historically significant for its antiscorbutic properties due to high vitamin C content in the bark, D. winteri was used by European explorers in the late 16th century to treat scurvy, earning its common name from John Winter's voyage with Francis Drake in 1578. Indigenous Mapuche people in Chile and Argentina revere it as sacred, using it as a spice similar to pepper and in traditional medicine for ailments like indigestion, colic, and fevers. The aromatic pungent bark has been powdered and used as a pepper substitute in Brazil, Chile, and Argentina.
W. salutaris extracts contain a collection of bioactive molecules, including several unique drimane-type sesquiterpenoids such as warburganal, polygodial, muzigadial, ugandensidial, and isomukaadial acetate. These compounds are broadly considered the primary pharmacologically active constituents of the plant.
Drimane sesquiterpenes that have been isolated from W. salutaris include 11α-hydroxycinnamosmolide, isopolygodial (isotadeonal), warburganal, polygodial, salutarisolide, muzigadial (cannelal), ugandensidial (cinnamodial), isopolygodial, and mukaadial. Other drimane-type sesquiterpenes isolated from W. salutaris include isodrimenol, drimenol, confertifolin, and a non-sesquiterpene monoaldehyde form of polygodial.
Analysis of bark samples from the Soutpansberg mountains demonstrated the presence of four drimane sesquiterpenoids—warburganal, mukaadial, polygodial, and isopolygodial—as well as the drimane sesquiterpene salutarisolide. Drewes et al. (2001), using a quantitative 1H NMR procedure, confirmed the presence of warburganal and polygodial in both leaves and bark samples from W. salutaris.
W. salutaris extracts contain drimane-type sesquiterpenoids such as warburganal, polygodial, muzigadial, ugandensidial, and iso-mukaadial acetate. These compounds, combined with other secondary metabolites such as monoterpenes, sesquiterpenes, and flavonoids, warrant further in vivo efficacy studies to irrefutably validate observed in vitro pharmacological activities and ethnobotanical usage of this plant. Antioxidant activity of the methanol extract of W. salutaris could possibly be due to the presence of flavonoid compounds. The bark is also a source of tannins. A study which evaluated the antioxidant and anti-ageing effects of W. salutaris identified 30 compounds in aqueous bark extracts using HPLC-MS analysis.
The bark contains drimane sesquiterpenoids such as warburganal and polygodial, both of which are known to be active against Candida. Polygodial is potentially useful in clinical medicine as an adjuvant to treatment with antibiotics and antifungals that have poor membrane permeability.
Muzigadial and warburganal have been found to not only have antifeedant properties, but also to be active against both fungi and bacteria. Kubo and Taniguchi (1988) demonstrated that polygodial, one of the major compounds in Warburgia species, was fungicidal rather than fungistatic.
Kubo (1995) found that the major compounds—warburganal, muzigadial, and polygodial—all demonstrated notable antifungal activities (at 100 µg/ml), while other sesquiterpenes including mukaadial, ugandensidial, epipolygodial, and others did not display noteworthy antifungal activity.
Mukaadial and warburganal contribute to the 5-lipoxygenase (5-LOX) inhibitory activity of W. salutaris. In another experiment, Frum (2006) demonstrated that W. salutaris bark has anti-inflammatory activity, with mukaadial and warburganal being partially responsible for the displayed anti-inflammatory activity of the plant species.
Due to its antioxidant properties, extracts of W. salutaris showed protective effects against crystalline silica-induced inflammatory cytokine expression, activation of nuclear transcription factor-κB, DNA strand breakage, and lipid peroxidation. Hence, W. salutaris may be a potential therapeutic agent against the fibrogenic and carcinogenic effects of crystalline silica.
Some drimane sesquiterpenes have been isolated from this plant: warburganal possesses molluscicidal, antifungal, and antibacterial activity; polygodial has antifungal and antibacterial activity; salutarisolide and muzigadial possess antimicrobial and antifungal properties; and 11α-hydroxycinnamosmolide has anti-mycobacterial activity.
Various studies have reported W. salutaris as having significant antibacterial, antifungal, antimycobacterial, anti-malarial, and antioxidant activities as well as anti-inflammatory properties. The extracts of Warburgia, particularly those from stem bark and leaves, exhibited a wide range of pharmacological effects, including antibacterial, antifungal, antimycobacterial, antioxidant, anti-inflammatory, antifeedant, antiplasmodial, antileishmanial, anthelmintic, cytotoxic, and molluscicidal activities.
A previous screening of South African medicinal plants showed that W. salutaris had promising antibacterial activity, and this endangered tree species was subsequently selected for bioassay-guided fractionation in order to identify the active principles. Fractionation of the ethyl acetate extract of the stem bark by chromatographic techniques yielded a sesquiterpenoid which exhibited antimicrobial activity against Gram-positive bacteria.
A study by Khumalo et al. (2019) assessed the antimicrobial activity of isolated compounds and leaf and bark extracts of W. salutaris. In addition to identifying warburganal, polygodial, and ugandensidial in bark extracts, the authors also identified 12α-acetal-polygodial, and the isolated compounds warburganal and mukaadial exhibited IC50 values of 61.86 µg/ml and >100 µg/ml, respectively, indicating that these two drimane sesquiterpenoids may be supporting the 5-lipoxygenase inhibitory activity of W. salutaris.
Muzigadial, which is one of the major phytochemicals found in Warburgia salutaris, has been observed to possess potent antibacterial activity. The totality of this antimicrobial evidence base is derived from in vitro laboratory studies; no controlled human clinical trials evaluating W. salutaris for infectious disease treatment have been published as of the most recent systematic reviews.
Evidence strength: Preliminary — in vitro only. W. salutaris extracts contain a collection of bioactive molecules such as sesquiterpenoids, drimane-type sesquiterpenes, and other terpenoids, which warrant further in vivo efficacy studies to irrefutably validate observed in vitro pharmacological activities and ethnobotanical usage of this plant.
The bark contains drimane sesquiterpenoids such as warburganal and polygodial, both of which are known to be active against Candida. Polygodial is potentially useful in clinical medicine as an adjuvant to treatment with antibiotics and antifungals that have poor membrane permeability. Muzigadial and polygodial were reported to be highly active against Staphylococcus and related fungi.
Evidence strength: Preliminary — in vitro only. The antifungal activity of W. salutaris extracts and isolated sesquiterpenoids has been consistently demonstrated in cell-based and laboratory assays, but clinical studies in humans are absent from the published literature.
Both polygodial and mukaadial displayed significant anti-inflammatory activities in vitro by lipoxygenase inhibition (Frum et al., 2005). Such activity is of relevance where intestinal inflammation is a targeted symptom.
Frum et al. (2005) tested leaf extracts of W. salutaris for antioxidant activity using the colorimetric method to test for DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity. Both aqueous and methanol extracts, with IC50 values of 34.43 ± 0.74 µg/ml and 15.38 ± 0.20 µg/ml, respectively, exhibited significant antioxidant activity.
Substantial antioxidant activity of W. salutaris extracts was observed in both DPPH and FRAP assays, comparable to the quercetin reference inhibitor, which the authors attributed to the high phenolic content of the extract.
Due to its antioxidant properties, extracts of W. salutaris showed protective effects against crystalline silica-induced inflammatory cytokine expression, activation of nuclear transcription factor-κB, DNA strand breakage, and lipid peroxidation. Hence, W. salutaris may be a potential therapeutic agent against the fibrogenic and carcinogenic effects of crystalline silica.
Evidence strength: Preliminary — in vitro only. Anti-inflammatory and antioxidant properties have been demonstrated in multiple laboratory-based assays, with a plausible mechanistic basis in 5-LOX inhibition and free radical scavenging. No human clinical trials have been conducted.
A study published in Malaria Journal (2018) focused on the evaluation of anti-malarial agents from Warburgia salutaris stem bark. The stem bark was extracted with dichloromethane, followed by silica gel column chromatography, which led to the isolation of iso-mukaadial acetate, a drimanoid sesquiterpene.
Both the W. salutaris bark extract (IC50 0.01 µg/ml) and iso-mukaadial acetate (IC50 0.44 µg/ml) displayed potent antiplasmodial activity against a chloroquine-sensitive Plasmodium falciparum strain. In addition, in vivo antiplasmodial studies using male Sprague-Dawley rats infected with Plasmodium berghei showed that W. salutaris reduced the percentage of parasitaemia in comparison to the control, and had protective effects on the survival of the P. berghei-affected animals.
In drug discovery, a compound is considered a success if it has an IC50 ≤ 1 µg/ml and a selectivity index that is at least ten times more active on the parasite than on human cell lines. Iso-mukaadial acetate shows good in vitro anti-malarial activity. There has been no report of any other isolated anti-malarial compound from W. salutaris in the literature at the time of publication.
Evidence strength: Preliminary — in vitro and animal studies only. While the antiplasmodial findings are promising and have progressed to animal models, no human clinical trials have been conducted.
A study published in the journal Biomolecules (2019) investigated the antidiabetic potential of the crude DCM extract from the stem bark of Warburgia salutaris as well as pure iso-mukaadial acetate, which had previously been investigated for antimalarial activity. Described as "pepper bark" due to its peppery taste, W. salutaris is distributed in the Southern Africa region, where it is traditionally used to treat diseases such as diabetes, fever, colds, flu, coughs, and chest infections. In vitro assays with L6 skeletal muscle cells were used to test for cytotoxicity, glucose utilisation, and western blot analysis.
Evidence strength: Very preliminary — in vitro only. The antidiabetic investigation is in an early laboratory stage, and no clinical data exist.
Owing to its widespread traditional use, a range of in vivo and in vitro bioactivities has been investigated including antimicrobial, antiparasitic, anti-inflammatory, antioxidant, and anticancer activities. W. salutaris extracts show variable cytotoxicity, necessitating further research.
Evidence strength: Preliminary — in vitro, variable, and inconclusive. Cytotoxic findings are inconsistent across studies and methodologies. No clinical oncology trials involving W. salutaris exist in the published literature.
Pharmacological results have validated the use of this genus in traditional medicine in a general sense. However, further investigations are needed to explore the bioactive compounds responsible for the in vitro and in vivo pharmacological effects and their mode of action. The entirety of the current scientific evidence base for W. salutaris rests on in vitro (cell-based) studies and a limited number of animal model experiments. No randomized controlled trials, systematic reviews of clinical evidence, or large-scale human pharmacokinetic studies have been published. Regulatory bodies such as the WHO, EMA, EFSA, and the NIH Office of Dietary Supplements have not issued monographs or evidence-based assessments for Warburgia salutaris.
Based on published ethnobotanical records and in vitro/preclinical research, Warburgia salutaris has been associated with the following body systems and health areas:
Warburgia salutaris is commercially available in crude form, as an essential oil, and in other dosage forms in over-the-counter products. No standardized clinical dosages have been established for any indication, as no human clinical trials have been conducted.
The following dosage figures appear specifically within preclinical research:
These values are laboratory-derived parameters and cannot be extrapolated to human therapeutic doses without clinical bridging studies, which are currently absent from the literature.
Although the toxicity of Warburgia remains poorly investigated, the genus has been contra-indicated in pregnancy. W. salutaris extracts show variable cytotoxicity, necessitating further research. Formal toxicological profiling in humans is absent; the cytotoxic potential of isolated sesquiterpenoids observed in cell-line studies means that safety in extended human use has not been formally characterised.
No published data from human pharmacokinetic or pharmacodynamic interaction studies are available. Polygodial has been noted as potentially useful as an adjuvant to treatment with antibiotics and antifungals that have poor membrane permeability, which implies a potential for altered membrane dynamics that could theoretically influence drug absorption, though this has not been studied in humans.
The pepper bark tree is one of the most highly valued medicinal plant species worldwide. Native to southern Africa, this species has been extensively harvested for bark widely used in traditional health practices. Illegal harvesting coupled with habitat degradation has contributed to fragmentation of populations and a severe decline in its distribution.
Warburgia salutaris is categorised as Endangered on the IUCN Red List, primarily because of reduction in population size based on decline in area of occupancy, extent of occurrence and/or quality of habitat, and actual or potential levels of exploitation. It is categorised as vulnerable in Mozambique, endangered in Malawi and South Africa, critically endangered in Swaziland, and extinct in the wild in Zimbabwe.
Due to its wide range of medicinal uses, this tree is over-harvested in the wild, which has caused an estimated 50% decline in the South African population, with some subpopulations nearly extinct. Field surveys in Swaziland found that of 700 mature individuals recorded, 263 (38%) had been ring-barked and 7% were felled and debarked. Juveniles were also ring-barked where mature individuals had been destroyed. Such indiscriminate harvesting was observed only in unprotected areas, and all respondents attributed it to illegal trade.
The most significant threat to W. salutaris is the overharvesting of bark and roots for traditional medicinal use. The tree can tolerate some harvesting by producing coppice shoots and regrowing stripped bark, but excessive harvesting can cause the death of the tree. Overuse of the bark has resulted in the species being listed as extinct in the wild in Zimbabwe and locally in some regions of KwaZulu-Natal, South Africa.
Warburgia salutaris (pepper bark tree) is a protected species in South Africa, and this review includes W. salutaris because of the multitude of medicinal purposes it is used for and because of its scarcity in South Africa, which resulted from the overharvesting of bark for the medicinal plant trade.
In South Africa, W. salutaris has become extremely scarce due to overharvesting, and occurrences of W. salutaris bark in the urban medicinal trade markets are mainly due to imports from other countries. Several health issues can be treated with W. salutaris, but its bark is the most commonly used part, harvested by stripping it vertically from the tree. Senkoro et al. proposed many conservation strategies to support the species' sustainable usage, including the adoption of alternate species for the same use, the replacement of bark with leaves, and the cultivation of other species.
W. salutaris is usually resilient to high levels of bark harvesting, with 75% of heavily harvested stems (>10% of the stem below 2 m) observed to have coppiced (resprouted) in one study. However, the threshold between sustainable and fatal harvesting is readily exceeded under commercial pressure.
Various studies have reported W. salutaris as having significant antibacterial, antifungal, antimycobacterial, antimalarial, and antioxidant activities as well as anti-inflammatory properties. Modern scientific research has shed light on its complex phytochemical composition and pharmacological properties. However, W. salutaris extracts contain a collection of bioactive molecules such as sesquiterpenoids, drimane-type sesquiterpenes, and other terpenoids, which warrant further in vivo efficacy studies to irrefutably validate observed in vitro pharmacological activities and ethnobotanical usage of this plant.
W. salutaris extracts contain a collection of bioactive molecules, including several unique drimane-type sesquiterpenoids. These compounds, combined with other secondary metabolites such as monoterpenes, sesquiterpenes, and flavonoids, warrant further in vivo efficacy studies to irrefutably validate observed in vitro pharmacological activities and ethnobotanical usage of this plant.
Critical gaps include: the absence of any published randomized controlled trials or human pharmacokinetic data; the lack of formal toxicology studies adequate to support safe human dosage recommendations; the need for bioavailability and metabolic profiling of the key sesquiterpenoids in humans; and the urgent need to reconcile conservation imperatives with ongoing commercial demand — a challenge that several research groups have identified as a potential driver toward using leaf-based preparations as a more sustainable alternative to bark stripping.
Health conditions that Pepper bark tree may help support.
Body systems that Pepper bark tree may help support.
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