Wintergreen

Wintergreen (Gaultheria procumbens L.): A Comprehensive Reference

1. Identity: Botanical Classification, Common Names, and Forms

1.1 Botanical Identity

Gaultheria procumbens, also called the eastern teaberry, the checkerberry, the boxberry, or the American wintergreen, is a perennial species of Gaultheria native to northeastern North America from Newfoundland west to southeastern Manitoba, and south to Alabama. It is a member of the Ericaceae (heath family). It is a small, low-growing shrub, typically reaching 10–15 cm (4–6 in) tall, with evergreen, elliptic to ovate leaves measuring 2–5 cm long and 1–2 cm broad, with a distinct oil of wintergreen scent.

Most species of the shrub genus Gaultheria demonstrate this characteristic and are called wintergreens in North America, the most common generally being the American wintergreen (Gaultheria procumbens). The term "wintergreen" is also applied to related species in the same genus. A similar high contribution of methyl salicylate is observed for essential oils obtained from other Gaultheria species, and therefore all Gaultheria essential oils, regardless of the plant organs and species used for distillation, are called "wintergreen oils."

1.2 Principal Chemical Identity

G. procumbens, classified as an essential oil-bearing plant, is characterised by a significant essential oil content, which is 1.30% dry weight (dw) for leaves and 2.68% dw for fruits, respectively. The dominant component of the essential oil is methyl salicylate, constituting almost 99% of the entire complex. Wintergreen oil is a pale yellow or pinkish fluid liquid that is strongly minty aromatic described as "fresh, sweet, and characteristically wintergreen" with components including methyl salicylate (about 98%), α-pinene, myrcene, delta-3-carene, limonene, 3,7-guaiadiene, and delta-cadinene.

For the leaves to yield significant amounts of their essential oil, they need to be fermented for at least three days. The berries and leaves contain methyl salicylate, a compound that is closely related to aspirin.

1.3 Common Preparations and Forms

Wintergreen is available and used in several distinct forms:

• Essential oil (wintergreen oil): Steam-distilled or vacuum-distilled from the leaves of Gaultheria procumbens, wintergreen has a long history in Native American medicine for pain relief and respiratory support.
• Topical OTC preparations: Methyl salicylate (oil of wintergreen) is widely available in many over-the-counter liniments, ointments, lotions or medicated oils for the relief of musculoskeletal aches and pains.
• Food flavoring: Wintergreen is a common flavoring in American products ranging from chewing gum, mints, and candies to smokeless tobacco such as dipping tobacco, and it is a common flavoring for dental hygiene products such as mouthwash and toothpaste.
• Herbal leaf preparations: Leaves have historically been brewed into teas or used in poultices; wintergreen leaf preparations capitalize on the presence of gaultherin and other salicylate glycosides, as well as additional active compounds like procyanidins and flavonoids.
• Transdermal patches: OTC topical analgesic patches available on the market list methyl salicylate at concentrations ranging from 0.04% to 20%, and wintergreen oil at 0.5%, among their active ingredients.

2. Traditional and Historical Use

2.1 Indigenous North American Use

G. procumbens was known and used by the indigenous people of the North American continent, who probably noticed its characteristic smell and sumptuous, red, berry-like fruits. The Chipewyan, Iroquois, Menominee, Pottawatomi, and Seneca Indian tribes used G. procumbens as a food source and as an antipyretic and anti-rheumatic drug.

Native Americans used the plant to treat a variety of ailments, including colds, headaches, stomach aches, chronic indigestion, kidney disorders, and rheumatism. The leaves were used to make tea by several Native American groups, including the Algonquin, Chippewa, Ojibwa, and Cherokee. The Iroquois mashed the fruit, made it into small cakes, and dried the cakes for future use.

Traditionally, Native American communities used both the berry and leaf internally, eating the fresh berries as a food, or brewing an infusion of the leaves to treat rheumatic conditions, headaches, fevers and sore throats. Wintergreen was also used commonly in gargles, mouthwashes and poultices due to its antiseptic properties, and to this day is still used in sports injury lotions and gels, and some dental care products.

2.2 Colonial and Post-Colonial Use

The colonists quickly noticed the delicately fragrant shrub and adapted it as a medicinal plant. The plant has been used for hundreds of years in traditional medicine to treat disorders connected with inflammation or infection, especially rheumatoid arthritis, influenza, the common cold, and fever.

Historical reports on the chemical composition date back to the second half of the 19th century and relate mainly to methyl salicylate as the dominant component of G. procumbens essential oil (wintergreen oil).

2.3 Scope of Ethnomedicinal Use

G. procumbens and other Gaultheria species, as well as methyl salicylate-rich essential oils distilled from the plants, are used (both externally and internally) in the treatment of disorders connected with inflammation, pain, and/or infection, including rheumatoid arthritis, influenza, the common cold, tracheitis, pharyngitis, pleurisy, fever, prostatitis, swelling and muscular pain, and some skin and periodontal problems.

Wintergreen oil is also used externally to cure lumbago, sciatica, and muscle aches. In modern Western herbal practice, wintergreen is used externally only, primarily to treat both musculoskeletal and neurological pain and inflammation.

3. Key Constituents and Active Compounds

3.1 Volatile Fraction

Over 130 volatile compounds have been detected in wintergreen oil with dominating methyl salicylate (96.9–100%). Methyl salicylate is the ester formed from methanol and salicylic acid; following application, methyl salicylate rapidly penetrates the skin, and in the epidermis and dermis it undergoes hydrolysis, leading to the formation of active salicylic acid.

3.2 Glycosidic Salicylates

Chemotaxonomically, representatives of the genus Gaultheria are characterized by the abundance of methyl salicylate 2-O-(6′-O-β-D-xylopyranosyl)-β-D-glucopyranoside (gaultherin) and/or its structural analogues differing in glycosidic sugar components. Gaultherin is the predominant glycoside form of salicylate in the plant tissue. Wintergreen contains extraordinarily high concentrations of salicylates, which can reach concentrations of over 1% of the fresh weight of the tissue, and the predominant form of this salicylate is gaultherin.

Gaultherin [methyl salicylate 2-O-β-D-xylopyranosyl-(1→6)-β-D-glucopyranoside] is a natural salicylate found in some plant species belonging primarily to the Ericaceae and Rosaceae families. Biological studies conducted since the beginning of the 21st century have suggested the potential use of gaultherin in treating various diseases related to inflammation and oxidative stress, including rheumatoid arthritis, sciatica, neuralgia, and muscular pain. The accumulated results indicated a targeted range of biological effects, particularly anti-inflammatory, antipyretic, and anti-rheumatic properties associated with reduced adverse outcomes.

3.3 Polyphenolic Fraction

Later phytochemical research allowed the identification of over 70 bioactive constituents classified as simple phenolic acids, chlorogenic acid isomers, methyl salicylate glycosides, flavonoids, and proanthocyanidins among polyphenols, as well as triterpene acids and sterols.

The reviewed papers indicate that chemical constituents responsible for the biological activity of eastern teaberry include polyphenols such as methyl salicylate glycosides, free flavan-3-ols and procyanidins, flavonoids, and phenolic acids with dominant isomers of chlorogenic acids, but also triterpenes including ursolic and oleanolic acids.

Comprehensive UHPLC-PDA-ESI-MS3 and HPLC-PDA studies led to the identification of 35 polyphenols, with a procyanidin A-type trimer, quercetin 3-O-glucuronide, isomers of caffeoylquinic acids, and (−)-epicatechin being the dominant components. Additional constituents identified include gaultherin (GT) from the methyl salicylate glycoside group; (−)-epicatechin (ECA) from the group of monomeric flavanols; procyanidin B2 and a procyanidin A-type trimer as oligomeric proanthocyanidins; chlorogenic acid, neochlorogenic acid, and cryptochlorogenic acid as three isomeric caffeoylquinic acids; and miquelianin (MQ), hyperoside (HY), and a quercetin pentoside-glucuronide as flavonoid glycosides.

UHPLC-PDA-ESI-MS3, HPLC-PDA, and UV-photometric assays revealed that the acetone extract of G. procumbens stems accumulates a rich polyphenolic fraction of 35 identified constituents with a total content of 427.2 mg/g dry weight, mainly flavanols (catechins and proanthocyanidins; 201.3 mg/g dw) and methyl salicylate glycosides (199.9 mg/g dw).

3.4 Triterpene Fraction

Aliphatic compounds, triterpene acids, and sterols have been revealed in lipophilic fractions of the plant. The triterpene acids ursolic acid and oleanolic acid, identified in aerial parts including leaves, stems, and fruits, contribute additional biological activity to the plant's overall profile.

4. Mechanisms of Action

4.1 Methyl Salicylate: Counterirritant and Rubefacient Mechanisms

Salicylates, such as methyl salicylate, trolamine salicylate, and oil of wintergreen (liquid methyl salicylate), are counterirritants thought to work through sensory nerve modulation and localized inflammation. Based on the principle of counterirritation, methyl salicylate has been suggested to have therapeutic effects by triggering irritation or cutaneous pain to mitigate pain of subdermal origin; however, the precise underlying physiological mechanisms are not fully understood.

The findings from recent research indicate that topical methyl salicylate induces short-term cutaneous vasodilation, but it may not enhance skeletal muscle blood flow. This study highlights the complex sensory responses to its application, which may be based on the short-term modulation of thermosensitive transient receptor potential channels.

Topical salicylates are considered to act primarily as rubefacients. Several studies have recognized methyl salicylate as a vasoactive compound that increases local blood flow and raises skin or tissue temperature.

4.2 COX Inhibition and Cytokine Modulation

Strong anti-inflammatory activity is attributed to the main components of the natural American wintergreen essential oil. Methyl salicylates from Gaultheria procumbens possess similar anti-inflammatory potency analogous to aspirin. In vitro and in vivo assays, methyl salicylates reduce cyclooxygenase 2 (COX-2), IL-8, IL-1β and TNF-α production.

The molecular mechanisms of gaultherin involve influence on several signalling pathways, including NF-κB, MAPK, and potentially AMPK, as well as the inhibition of critical pro-inflammatory enzymes, such as COX-2.

The pure GT (gaultherin) and its analogues isolated from G. yunnanensis have been demonstrated to exert anti-inflammatory effects by inhibiting the production of ROS and pro-inflammatory cytokines (TNF-α, IL-6, and IL-1β) and by suppressing the activation of the NF-κB signaling pathway in vitro.

Methyl salicylate glycosides reduced the level of ROS induced by LPS, and these results showed that the isolated compounds possess anti-inflammatory properties through inhibition of the production of pro-inflammatory cytokines, NO, and ROS.

4.3 Action of the Polyphenolic Fraction

The extract from G. procumbens reveals promising potential as a direct inhibitor of three pro-inflammatory enzymes (HYAL, COX-2, and LOX) and a modulator of pro-oxidant and pro-inflammatory functions of neutrophils stimulated by LPS, fMLP, and fMLP-cytochalasin B, primarily influencing the ROS levels.

The accumulated research indicates that mainly hydrophilic non-volatiles are responsible for the pharmacological effects of G. procumbens, primarily its potent anti-inflammatory, antioxidant, and photoprotective activity, with mechanisms verified in vitro and ex vivo in cellular and cell-free assays.

4.4 Systemic Conversion After Absorption

In vivo, methyl salicylate is hydrolyzed to salicylic acid. The primary effects of salicylate toxicity are complex and include direct stimulation of the CNS respiratory center leading to a respiratory alkalosis. Salicylates also uncouple oxidative phosphorylation at a cellular level, producing an increased metabolic rate. This results in increasing oxygen consumption, glucose utilization, and heat production. Salicylates inhibit the Krebs cycle and alter lipid metabolism and amino acid metabolism, producing lactic acid and ketones with resultant metabolic acidosis. These mechanisms are relevant primarily in the context of overdose and toxicity, not at therapeutic topical doses.

5. Scientific Evidence by Area of Use

5.1 Topical Analgesia and Musculoskeletal Pain

Topical formulations containing methyl salicylate have been shown to be effective in the treatment of muscle strain, temporomandibular joint and masseter muscle pain. As an over-the-counter drug ingredient, the FDA has recognized methyl salicylate as a topical counterirritant for the temporary relief of minor aches and pains associated with muscles and joints.

However, the broader evidence base for topical salicylates in musculoskeletal conditions is not unequivocally positive. A Cochrane review failed to show any benefit from topical salicylates for acute or chronic conditions, thus limiting their use for musculoskeletal conditions. Based on available evidence, topical salicylates are not an effective alternative for patients with musculoskeletal pain; the strength of recommendation against their use is level B. Studies of topical analgesics are limited in quality.

A multicenter real-world phase IV clinical trial of compound methyl salicylate liniment (Ammeltz) in China provides further data. Of 3,600 subjects enrolled, 3,515 (97.64%) completed the study. A total of 277 adverse events occurred in 258 subjects (7.28%), with the most common adverse events including upper respiratory infections (130 cases, 3.67%), local pruritus (17 cases, 0.48%), and diarrhea (12 cases, 0.34%). Visual analog scale scores were used to assess pain relief outcomes in this study, though it involved a compound formulation rather than methyl salicylate in isolation.

Evidence strength: The use of methyl salicylate as a topical counterirritant/rubefacient in OTC products is FDA-recognized, but controlled clinical trial evidence specifically for wintergreen-derived methyl salicylate is limited. A Cochrane review found insufficient evidence for benefit in musculoskeletal conditions for topical salicylates as a class. The mechanistic rationale (counterirritant, prostaglandin inhibition, vasodilation) is well established in vitro and in vivo, but high-quality clinical trial evidence remains sparse.

5.2 Anti-Inflammatory Effects

The available results showed that extracts from leaves, stems, and fruits of G. procumbens were strong anti-inflammatory and antioxidant agents that inhibited pro-inflammatory enzymes, scavenged free radicals in vitro, and downregulated the pro-inflammatory functions of human cells ex vivo.

The anti-inflammatory activity is the leading biological effect of G. procumbens, as suggested by traditional medicine, so most literature data have been devoted to this topic. The biological effectiveness of the dominant methyl salicylate glycoside—gaultherin—has also been confirmed in animals.

Evidence strength: Anti-inflammatory activity has been robustly demonstrated in vitro (cell-free assays) and ex vivo (human neutrophil models) for both extracts and isolated constituents. Animal studies have confirmed gaultherin's activity. However, there is an absence of in vivo studies, especially clinical trials concerning effective dose determination and toxicological verification and technological research, including drug formulation. The anti-inflammatory evidence base for G. procumbens extracts specifically (as opposed to methyl salicylate alone) is therefore preliminary and pre-clinical.

5.3 Antioxidant Activity

Activity parameters of the extracts correlated strongly with the levels of total phenolics (72.4–270.7 mg GAE/g), procyanidins, and phenolic acids, whereas for flavonoids only moderate effects were observed. Wintergreen oil is reported as a potent anti-inflammatory agent exhibiting moderate antioxidant and antimicrobial activity in vitro.

Evidence strength: Antioxidant activity of G. procumbens extracts has been confirmed in multiple in vitro assays. No human clinical evidence exists. The antioxidant activity of the essential oil itself is characterized as only moderate in these studies.

5.4 Antimicrobial Activity

The antimicrobial activity of wintergreen essential oil was evaluated against a panel of Gram-positive and Gram-negative bacteria, as well as Candida spp., using disc diffusion and broth microdilution assays. The oil exhibited moderate to strong antimicrobial effects, with the highest inhibition zones recorded for Staphylococcus aureus (15.67 mm) and Listeria monocytogenes (14.67 mm). MIC50 values ranged from 0.34 mg/mL for Yersinia enterocolitica to 6.75 mg/mL for L. monocytogenes.

The biological activity studies were mainly focused on the antimicrobial potential, such as antibacterial, antifungal, insecticidal, and larvicidal activities of the wintergreen oil.

Evidence strength: Antimicrobial activity is confirmed only in laboratory (in vitro) settings. No clinical trials have evaluated wintergreen oil or extracts for the prevention or treatment of microbial infections in humans.

5.5 Photoprotective Activity

Recent studies indicated that the extracts from leaves, stems, and fruits of G. procumbens (5–50 μg/mL) were strong photoprotectors. Apart from the antioxidant effects revealed under UV-irradiation, their biological mechanism involved enhancing the viability of UVA-irradiated human Hs68 dermal fibroblasts and reducing the percentage of tail DNA in Hs68 cells as documented by CCK8 assay and the comet assay, respectively. At the same time, the results showed that G. procumbens leaf, stem, and fruit extracts (5–25 μg/mL) did not affect the wound healing process, as they did not enhance fibroblast migration measured by scratch assay.

Evidence strength: Photoprotective effects have been demonstrated in cell-based (in vitro) assays only. There are no human clinical data in this area.

5.6 Oral and Dental Applications

Various traditional uses include use for gingivitis and periodontitis. Wintergreen's antiseptic properties have been exploited in dental care products; it is a common flavoring for dental hygiene products such as mouthwash and toothpaste.

Evidence strength: Topical antimicrobial and anti-inflammatory mechanisms provide a plausible rationale for use in oral hygiene products, but there are no dedicated clinical trials evaluating wintergreen preparations specifically for dental or periodontal outcomes.

6. Body Systems and Health Areas

• Musculoskeletal system: The primary contemporary application. Used topically for joint pain, arthritis, muscle soreness, back pain, sciatica, and lumbago, based on methyl salicylate's counterirritant and rubefacient properties.
• Nervous system (pain perception): Sensory responses to methyl salicylate application may be based on the short-term modulation of thermosensitive transient receptor potential (TRP) channels.
• Cardiovascular/circulatory system: Several studies have recognized methyl salicylate as a vasoactive compound that increases local blood flow and raises skin or tissue temperature. Due to its structural kinship with aspirin, it also carries antiplatelet potential at systemic concentrations, contributing to bleeding risk.
• Immune/inflammatory system: Broad in vitro and ex vivo evidence demonstrates inhibition of key pro-inflammatory pathways (NF-κB, COX-2, LOX, HYAL) and cytokines (IL-1β, IL-6, TNF-α).
• Respiratory system: Used traditionally for colds, influenza, and respiratory infection; wintergreen oil (applied in appropriate, relatively low concentrations) remains indicated only for external use for the relief of musculoskeletal pain and to treat influenza, fever, and the common cold.
• Skin: In vitro evidence supports antioxidant, antimicrobial, and photoprotective effects relevant to skin health; used in cosmetic and topical analgesic formulations.
• Gastrointestinal system: Used historically for digestive complaints, though internal use of concentrated oil is contraindicated due to toxicity.

7. Dosage Forms and Reported Dosages

Dosing recommendations for oral or topical administration of wintergreen oil are not available from authoritative sources. Wintergreen has generally recognized as safe (GRAS) status when used as a flavoring agent in foods; dosages higher than those found in food should be avoided.

For topical OTC products, the following concentrations have been documented in regulatory and clinical records:

• OTC topical analgesic patches list methyl salicylate (MS) at concentrations of 0.04%–20%, and wintergreen oil at 0.5%.
• Over-the-counter products may contain up to 30% methyl salicylate.
• One FDA-approved patch formulation is 7 cm × 10 cm and contains 10% methyl salicylate and 3% L-menthol.

In the multicenter Chinese real-world study of compound methyl salicylate liniment, visual analog scale scores were evaluated to assess the severity of pain and the pain relief rate was used to evaluate the efficacy of the study drug. The study did not specify a single standardized dose for methyl salicylate in isolation.

In photoprotective studies, extracts from leaves, stems, and fruits of G. procumbens were tested at concentrations of 5–50 μg/mL. G. procumbens leaf, stem, and fruit extracts were tested at 5–25 μg/mL in wound healing assays. These are in vitro values and do not correspond to human dosages.

8. Safety Considerations and Drug Interactions

8.1 Oral Toxicity

Wintergreen oil is highly concentrated, lipid soluble, and able to pass through the skin, posing a threat of severe, rapid-onset salicylate poisoning. The toxic potential of topical medicaments containing methyl salicylate or wintergreen oil should be fully appreciated. When ingested, highly concentrated liquid methyl salicylate in the form of wintergreen oil can induce vomiting and cause severe, often fatal, poisoning.

1 mL of wintergreen oil is equivalent to 1.4 g of aspirin; therefore, 5 mL of wintergreen oil is equivalent to approximately 7 g of aspirin (which is the equivalent of 21.5 aspirin [325 mg] tablets).

Ingestion of greater than a lick or taste of oil of wintergreen (98% methyl salicylate) by children under 6 years of age, and more than 4 mL of oil of wintergreen by patients 6 years of age and older, could cause systemic salicylate toxicity and warrants referral to an emergency department.

8.2 Salicylate Toxicity Syndrome

The clinical presentation of salicylate poisoning is related to stimulation of the central nervous system respiratory center, disturbance of lipid and carbohydrate metabolism, and disturbance of intracellular respiration. Symptoms can include hyperpnea, tachypnea, tinnitus, hyperpyrexia, and diaphoresis. Additional signs are dehydration, electrolyte disturbances, serum glucose abnormalities, and mixed acid-base disturbances. More severe toxicity can result in acute lung injury, lethargy, coma, seizures, cerebral edema, and death.

Treatment of salicylate poisoning consists of general supportive care, gastrointestinal decontamination with activated charcoal in cases of salicylate ingestion, and monitoring of serum salicylate concentrations. Enhanced elimination of salicylate is achieved by a sodium bicarbonate infusion with maintenance of serum potassium homeostasis or hemodialysis if the bicarbonate infusion is ineffective or cannot be performed.

8.3 Topical Toxicity and Dermal Absorption

Topical salicylates rarely produce systemic toxicity when used appropriately; however, methyl salicylate can be absorbed through intact skin. Exercise and heat exposure can enhance percutaneous absorption of methyl salicylate. At least one death has been reported in an athlete using an excessive amount of a methyl salicylate-containing rubefacient.

A fatal case of acute methyl salicylate toxicity from both ingestion and dermal absorption of oil of wintergreen has been reported. This case highlights that topical absorption of salicylates, particularly in patients with renal failure, can result in severe intoxication. The case involved an 80-year-old man with end-stage renal disease who had oil of wintergreen (containing 35% mg/mL methyl salicylate) rubbed regularly on his lower extremities.

Methyl salicylate in topical analgesic preparations may cause irritant or allergic contact dermatitis and anaphylactic reactions. Second- and third-degree burns have been reported rarely with products containing menthol alone or menthol and methyl salicylate in concentrations greater than 3% menthol and 10% methyl salicylate.

8.4 Drug Interactions: Anticoagulants

Excessive usage of topical methyl salicylate preparations in patients receiving warfarin may result in adverse interactions and bleedings. In case reports and case series, topical administration of methyl salicylate has been reported to cause increases in international normalized ratio (INR) as high as 12.2 when coadministered with warfarin, resulting in bruising, retroperitoneal bleeding, and GI bleeding.

8.5 Hypersensitivity and Aspirin Sensitivity

One case report documents a potential hypersensitivity reaction in a nonsmoking, 21-year-old woman with a history of asthma who complained of wheezing, dry cough, and bronchial pain after using a tartar-control toothpaste flavored with wintergreen oil. Another case report documents the development of laryngeal edema in an individual after accidental ingestion of wintergreen oil. Because wintergreen oil is absorbed and converted to salicylic acid after both oral and topical administration, it should be used with caution in individuals with nonallergic aspirin sensitivity.

People who are allergic to aspirin or other salicylate compounds, or who have asthma or nasal polyps, may experience allergic reactions to wintergreen.

8.6 Populations Requiring Special Caution

Wintergreen leaf and oil are likely unsafe when taken by mouth in children. Taking as little as 4 mL (less than a teaspoon) of wintergreen oil by mouth can be fatal. Wintergreen oil is likely unsafe when applied to the skin of children less than 2 years old.

Wintergreen can be toxic when ingested, particularly during pregnancy in higher doses, and has been connected to pediatric deaths. Based on rodent models, methyl salicylate, the active constituent in wintergreen, has negative reproductive effects and should be avoided in pregnancy.

Wintergreen is likely unsafe when taken by mouth or used on the skin as a medicine while breast-feeding, as it may be toxic to nursing infants.

Chronic dermal application of some salicylate-containing products can produce systemic salicylate toxicity. This risk is heightened in individuals with renal impairment, as noted in the case reports above.

8.7 GRAS Status and Regulatory Classification

Wintergreen has Generally Recognized As Safe (GRAS) status when used as a flavoring agent in foods. This GRAS designation applies specifically to food flavoring quantities, which are vastly smaller than medicinal doses.

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