Gumweed

Gumweed (Grindelia spp.): A Comprehensive Reference

1. Identity, Taxonomy, and Botanical Description

Common name: Gumweed (also gum plant, rosinweed, tarweed, resinweed, August flower, and Spanish gold). The botanical name covers several closely related species, principally Grindelia camporum, G. robusta, G. squarrosa, G. integrifolia, G. humboldtii, and G. hirsuta (syn. G. humilis). The genus name Grindelia honors David Hieronymus Grindel (1776–1836), a botanist, chemist, and pharmacist.

Grindelia is a genus of plants native to the Americas and belongs to the family Asteraceae (Compositae). The genus is made up of around 73 species, naturally ranging in western and central North America, Mexico, and South America, but introduced to eastern North America and the Old World. Grindelia squarrosa (Pursh) Dunal, commonly called curlycup gumweed, is a short-lived herb or subshrub with oblong to oblanceolate, crenulate-serrulate leaves (1.5–7 cm long and 0.5–1.3 cm wide), ranging throughout the Great Plains, Rocky Mountains, and Great Basin areas of North America. The plant has been introduced elsewhere and has become an invasive species in central Europe.

Grindelia camporum is a species of flowering plant in the daisy family known by the common names Great Valley gumplant and Great Valley gumweed; the plant is native to California and Baja California, where it can be found in a number of habitats including chaparral and woodlands. It is a gangly perennial topping 2 m (6 ft.) in maximum height, with erect, branching stems lined with many stiff, wavy-edged, serrated leaves 2 to 3 cm long, bearing single large flower heads up to 3 cm wide atop branch tips.

A defining visual characteristic of all medicinally used Grindelia species is the production of a conspicuous sticky latex. The immature flower heads ooze with a sticky white latex before opening into daisy-like flowerheads with spectacular yellow petals. This tacky residue is produced in multicellular glands and ducts coating the plants' flower heads and leaves — the principal reason for the common names gumweed, tarweed, and rosinweed.

Official Pharmacopoeial Recognition

Quality of Grindeliae herba is defined in the European Pharmacopoeia (Ph. Eur.): the herb of the Californian or Hairy Grindelia (G. hirsutula) and the herb of the Bulky Grindelia (G. squarrosa) may be used. The ESCOP herbal monograph (published 2015) defines the herbal drug as consisting of the dried flowering tops of Grindelia robusta Nutt., Grindelia squarrosa Dunal, Grindelia humilis Hook. et Arn., or Grindelia camporum Greene. Herba Grindeliae is official in France, England, Russia, Argentina, Venezuela, and Mexico. It was included in the U.S. Pharmacopoeia from 1882 to 1926, and in 1926 was introduced as an official drug in the U.S. National Formulary, where it remained until the 1960 edition.

Common Forms and Preparations

The aerial parts — primarily the dried flowering tops, leaves, and stems — are the plant parts used medicinally.

• People dry the leaves and top of the plant to make medicine.
• Herbal infusion (tea): Pour 150 mL of boiling water over 2 to 3 g of finely chopped Grindelia herb, leave to infuse for 10 to 15 minutes, and strain; drunk hot several times a day.
• Tincture: An alcohol-based liquid extract; historically the tincture was prepared at a strength of 1 part to 5.
• Fluid extract: A more concentrated liquid preparation used internally.
• Topical preparations: Diluted tinctures of Herba Grindeliae are used externally for acute dermatitis, including dermatitis caused by Rhus toxicodendron (poison oak/ivy).
• Poultice: A poultice made from the flowers or foliage has been used to treat skin rashes, minor burns, eczema, and dermatitis.

2. Traditional and Historical Use

Native American Traditions

Traditionally, Native American communities used G. squarrosa's leaves and flowers to treat respiratory conditions such as asthma, bronchial spasms, and whooping cough, attributing these effects to its resinous compounds. The Shoshoni used G. squarrosa in their traditional medicine; a decoction of the plant was used as a cough medicine, as an antiseptic wash, and taken internally as an expectorant, as well as to treat stomachache, smallpox, and measles.

The Chumash and Ohlone boiled the leaves and flower heads into a tincture or a tea for treating poison oak rash, dermatitis, wounds, burns, boils, and sores. The Cahuilla used them to cure colds, and Hispanic peoples for colds, rheumatism, kidney disorders, paralysis, and stomach disorders. The Blackfeet Nation refers to Gumweed as "akspeis," which translates to "stickyweed." The Blackfoot made a decoction or infusion of the above-ground plant for liver trouble. The fresh gum was also rubbed on the eyelids to treat snow-blindness.

Adoption into Western and Eclectic Medicine

Western herbal use of Grindelia was learned, as was common in the U.S., from indigenous medicinal use. When settlers learned of this medicinal plant from Native Americans, Grindelia was observed to be so effective that early physicians of Western medicine in the U.S. adopted its use. Practitioners in the United States did not recognize the real effectiveness and value of this plant until the middle of the 19th century; after this time, it came into prominence as a major therapeutic and medicinal herb, with official recognition coming with its inclusion in the Pharmacopoeia of the United States from 1882 to about 1926.

Pharmaceutical cigars containing Grindelia (e.g., Neumeier's cigarillos, 1913) were used for asthma; in addition to G. robusta, these contained cannabis, eucalyptus, datura, and tobacco leaves. In homeopathy, Grindelia is used for asthmatic conditions, chronic bronchitis, emphysema, and as a spleen remedy.

Monograph Classifications by Indication

The HMPC monograph lists traditional use for cough due to cold; the ESCOP monograph covers productive cough and catarrh of the upper respiratory tract; and the Commission E monograph covers catarrh of the upper respiratory tract.

3. Key Constituents and Active Compounds

The medicinally active material is concentrated primarily in the sticky latex coating the aerial parts, particularly the flower heads. Multiple compound classes have been identified:

Diterpenic Acids (Resin Fraction)

The main therapeutically active constituents in G. camporum appear to be borneol, several grindelic acids (around 30% volume), and several diterpenic acids, all of which appear in the sticky latex resin of the plant. Labdane diterpenoids — including grindelic acid, 6-oxogrindelic acid, and 17-hydroxygrindelic acid — have been isolated and identified from G. squarrosa. The ESCOP monograph notes that studies with the main characteristic constituents — a resin consisting of diterpenic acids, various grindelic acids, and borneol — are included in the evidence base.

Flavonoids

Identified flavonoids include acacetin, kumatakenin, quercetin, and hydroxycinnamic acids. The flavonoids quercetin and kaempferol have been attributed to anti-inflammatory actions, with the essential oil of Grindelia also found to have considerable antioxidant activity.

Volatile Oil (Essential Oil)

Compositional analysis of the essential oils of G. squarrosa revealed that the main components were α-pinene (24.7 and 23.2% in flower and leaf oils, respectively), limonene (10.0 and 14.7%), borneol (23.4 and 16.6%), p-cymen-8-ol (6.1 and 5.8%), β-pinene (4.0 and 3.8%), bornyl acetate (3.0 and 5.1%), and trans-pinocarveol (4.2 and 3.7%). Gas chromatographic analysis of G. squarrosa var. serrulata essential oil from southern Idaho confirmed it to be rich in monoterpenoids: α-pinene (21.9%), limonene (17.1%), terpinolene (10.6%), and borneol (6.5%).

Saponins and Alkaloids

Additional constituents include saponins (grindelin and the triterpenoid sapogenin lactone grindeliasapogenin D), the diterpene alkaloid grindeline (bitter), selenium, resin, and tannins. A saponin fraction has been isolated from the ethanolic extract of Grindeliae herba; the saponin fraction showed strong haemolytic activity — a finding relevant to in vitro safety assessments.

Selenium

Facultative indicator plant genera capable of accumulating selenium in high-selenium soils include Grindelia spp. (gumweed), which, while not requiring high selenium conditions to grow, can accumulate selenium concentrations above 50 μg/g in seleniferous soils. Great Valley gumweed may contain high levels of selenium, which is toxic when ingested in large amounts.

4. Mechanisms of Action

Anti-Inflammatory Pathways

The most mechanistically characterized activity of Grindelia extracts relates to modulation of inflammatory signaling. In cell-based studies, G. squarrosa extract significantly modulated pro-inflammatory functions of LPS-stimulated nasal and bronchial epithelium, resulting in decreased TLR-4 expression, decreased p65 NF-κB concentration, and inhibition of cytokine synthesis (IL-8, TNF-α, IL-1β, and IL-6) in both cellular models. Additionally, G. squarrosa extract slightly modulated ICAM-1 expression affecting macrophage attachment to epithelium, and was able to stimulate anti-inflammatory functions of macrophages by inducing TGF-β release and IL-10 receptor surface expression. Grindelic acid, identified as the dominant compound in the plant extract, also modulated pro-inflammatory functions of epithelium and macrophages, though to a lesser degree than the full extract.

Neutrophil Immunomodulation

Grindelia essential oils activated human neutrophils, resulting in increased intracellular calcium (EC₅₀ = 22.3 μg/mL for flower oil and 19.4 μg/mL for leaf oil); one of the major enantiomeric components, (−)-borneol, activated human neutrophil calcium influx (EC₅₀ = 28.7 ± 2.6 μM), whereas (+)-borneol was inactive. Furthermore, treatment with Grindelia essential oils inhibited activation of neutrophils by N-formyl peptide receptor 1 (FPR1) agonist fMLF and the FPR2 agonist WKYMVM; likewise, (−)-borneol inhibited FPR-agonist-induced calcium influx in neutrophils. The authors identified (−)-borneol as a novel modulator of human neutrophil function.

Expectorant and Antispasmodic Effects

The volatile oils may have irritant effects upon the kidneys, thus promoting diuresis, and have a topical rubefacient effect. Flavonoids are anti-inflammatory and possess some antimicrobial activity; the bitter taste increases the flow of saliva and other digestive secretions. The resinous diterpenic acids are thought to be responsible for the expectorant and antispasmodic effects attributed to the herb by empirical medicine and traditional practitioners, though the precise mechanism of bronchodilation has not been fully elucidated at the clinical level.

5. Scientific Evidence by Area of Use

5.1 Respiratory System: Cough, Bronchitis, and Upper Respiratory Tract Catarrh

This is the area with the longest institutional recognition and the largest body of supporting preclinical data. The ESCOP therapeutic indications for Grindeliae herba are productive cough and catarrh of the upper respiratory tract. The German Commission E monograph similarly covers catarrh of the upper respiratory tract, while the EMA HMPC monograph grants traditional-use status for cough due to cold.

At the in vitro/cell level, the most directly relevant study (Gierlikowska et al., 2021, published in Frontiers in Pharmacology) used LPS-stimulated human nasal and bronchial epithelial cell cultures: Significant modulation of pro-inflammatory functions of LPS-stimulated nasal and bronchial epithelium was observed; G. squarrosa extract treatment resulted in decrease of TLR-4 expression and p65 NF-κB concentration, and inhibition of cytokine synthesis (IL-8, TNF-α, IL-1β, and IL-6) in both cellular models. The authors concluded that the obtained results support the traditional use of Grindelia squarrosa preparations for treatment of cold-associated disease symptoms.

A related study published in Journal of Ethnopharmacology (Gierlikowska et al., 2020) examined both Inula helenium and Grindelia squarrosa: The study demonstrated that Inula helenium and Grindelia squarrosa, traditionally used in Europe as medicinal plants, are a valuable source of active compounds with anti-inflammatory activity. The study's ethnopharmacological context noted that over 90% of acute wheezing disease during epidemic season is associated with bronchial inflammation, and that both neutrophil- and eosinophil-mediated inflammation are involved in the pathophysiology of acute bronchitis, with neutrophil cell recruitment being dominant.

Evidence strength — respiratory: The institutional recognition (Commission E, ESCOP, EMA HMPC) is for traditional use, not well-established medicinal use, reflecting the lack of randomized controlled clinical trials (RCTs) in humans. The mechanistic cell-level data are supportive but not sufficient to establish clinical efficacy. People use gumweed for conditions such as cough, bronchitis, and asthma, but there is no good scientific evidence to support these uses. Overall, the respiratory evidence is categorized as preclinical (in vitro) plus traditional-use designation; no published RCTs in humans have been identified.

5.2 Antimicrobial Activity

Several in vitro studies have examined antimicrobial properties of Grindelia, with mixed results depending on solvent and preparation: Grindelia species were shown to exert antimicrobial activity, especially against gram-negative E. coli; extract of G. squarrosa flowers showed inhibition diameters in excess of 19.3 mm against A. caviae, M. luteus, and P. alvei. Using different extraction solvents (CCl₄ and 1-BuOH), G. squarrosa antimicrobial properties were confirmed: CCl₄ extract inhibited E. coli, S. aureus, and C. albicans growth, whereas 1-BuOH extract inhibited S. aureus, P. aeruginosa, and K. pneumoniae.

However, when a 60% ethanol extract was tested in the 2021 Frontiers in Pharmacology study: G. squarrosa extract (tested at 25–100 μg/mL) and grindelic acid (10–50 µM) did not inhibit bacteria growth; no growth inhibition zone (GIZ) or minimal inhibitory concentration (MIC) was detectable.

At the level of individual essential oil components: The major essential oil components were screened for antimicrobial activity against respiratory and dermal pathogens; (−)-β-pinene showed strong antibacterial activity against Streptococcus pneumoniae (MIC 39.1 μg/mL) and (−)-borneol showed strong activity against Staphylococcus species.

Evidence strength — antimicrobial: Results are inconsistent and entirely in vitro. Outcomes vary substantially by solvent system and preparation. No clinical antimicrobial studies exist. Evidence is preliminary and inconclusive.

5.3 Dermatology: Poison Oak/Ivy Dermatitis and Skin Conditions

The use of Grindelia for contact dermatitis from poison oak and poison ivy has both a well-documented traditional history and one published clinical case report. Poison oak and related hypersensitivity dermatitides are age-old problems historically treated with herbal medicines before the availability of corticosteroids; few of these historical therapies have been rigorously investigated; the case report (Canavan & Yarnell, 2005, Journal of Alternative and Complementary Medicine) provides some insight into the potential efficacy of certain herbs for relieving mild-to-moderate poison ivy dermatitis. Note that the senior author of this case report disclosed a financial conflict of interest as Vice-President of the tincture manufacturer whose products were used in the case. This report acknowledges that few historical therapies have been rigorously investigated and provides only limited insight into potential efficacy.

Diluted tinctures of Herba Grindeliae have traditional use externally for acute dermatitis caused by Rhus toxicodendron.

Evidence strength — dermatology: The strongest evidence consists of one published case report and traditional-use reports from multiple Native American cultures (Chumash, Ohlone, and others). No controlled trials exist. Evidence is anecdotal and weak from a modern clinical perspective.

5.4 Immunomodulation and Neutrophil Function

A 2022 study published in Molecules (Schepetkin et al., Montana State University) represents the most mechanistically detailed recent investigation into Grindelia's immunological activity: The study noted that while G. squarrosa is used in traditional medicine for treating various diseases, little was known about the immunomodulatory activity of its essential oils; the researchers isolated essential oils from the flowers and leaves and evaluated chemical composition and innate immunomodulatory activity. Treatment with Grindelia essential oils was found to inhibit activation of neutrophils by FPR1 agonist fMLF and the FPR2 agonist WKYMVM; the researchers identified (−)-borneol as a novel modulator of human neutrophil function.

Evidence strength — immunomodulation: The findings are preliminary and entirely in vitro/cell-based. No human trials have tested Grindelia for immune endpoints. Evidence is mechanistically interesting but clinically unestablished.

6. Body Systems and Health Areas Associated with Grindelia

• Respiratory system: Used by modern Western herbalists to support the health of the lungs, to relax and dilate airways, and to encourage the normal production and elimination of mucus (as an expectorant). The Commission E and ESCOP both recognize its traditional use for productive cough and upper respiratory catarrh.
• Integumentary system (skin): The Chumash and Ohlone boiled the leaves and flower heads for treating poison oak rash, dermatitis, wounds, burns, boils, and sores.
• Immune system: Grindelia extract and/or secondary metabolites demonstrated significant anti-inflammatory actions, with inhibition of inflammatory mediators including prostaglandins, interleukins, and tumor-necrosis factor.
• Urinary tract: Volatile oils may have irritant effects upon the kidneys, thus promoting diuresis. Grindelia has been used in some traditional contexts as a urinary tract disinfectant, though clinical evidence for this use is absent.
• Digestive system: The bitter taste of Grindelia increases the flow of saliva and other digestive secretions.

7. Dosage Forms and Dosages Reported in Sources

The following dosages are drawn directly from authoritative phytotherapy references and are reported here as found in those sources, not as recommendations:

• Dried herb (tea/infusion), oral: Pour 150 mL of boiling water over 2 to 3 g of finely chopped Grindelia herb, infuse for 10 to 15 minutes, strain; drink one cup hot several times a day, maximum 4–6 g/day.
• Daily dose range (dried herb), oral: The usual daily dose is between 4 and 6 g of the drug, 3 to 6 g of Grindelia fluid extract, and 1.5 to 3 mL of tincture.
• Historical tincture (19th century eclectic medicine): The tincture was prepared at the strength of 1 part to 5, with a dose of 6 to 25 drops (as cited in King's American Dispensatory, 1898).
• Topical application: Diluted tinctures of Herba Grindeliae are used externally for acute dermatitis. No standardized topical dosage is cited in the available pharmacopoeial sources.

8. Safety Considerations and Interactions

General Oral Safety

When taken by mouth, gumweed is possibly safe for most people, but it can cause some side effects such as stomach upset and diarrhea. In rare cases there may be irritation of the stomach lining. Reported adverse effects include allergic reaction and irritation of the gastrointestinal tract.

Topical Safety

There is not enough reliable information to know if gumweed is safe when applied to the skin or what the side effects might be.

Selenium Accumulation — A Specific Risk

One of the most factually well-documented safety concerns specific to Grindelia involves selenium bioaccumulation. Grindelia spp. are classified as "facultative indicator" plants — they do not require high selenium conditions to grow, but in high-selenium soils they can accumulate selenium concentrations greater than 50 μg/g. Great Valley gumweed may contain high levels of selenium, which is toxic when ingested in large amounts. The plant concentrates selenium from the soil and can be toxic when ingested by cattle, humans, and other mammals. This means that the selenium content of commercial Grindelia preparations may vary substantially depending on the soil origin of the plant material harvested; preparations sourced from seleniferous soils (common in parts of the Great Plains, Rocky Mountain region, and Intermountain West) carry higher risk.

Pregnancy and Lactation

Use during pregnancy and lactation and in children and adolescents under 18 years of age is contraindicated in the absence of data. Gumweed is not recommended in pregnant or breastfeeding women due to a lack of available scientific evidence.

Allergy Risk

Allergy to one of the ingredients of Grindelia preparations, or allergy to composite plants (Asteraceae), is a stated contraindication. Cross-reactivity with other Asteraceae family plants (e.g., ragweed, chamomile, chrysanthemum) is a theoretical concern consistent with known patterns of composite plant allergy, though Grindelia-specific cross-reactivity data in humans are lacking.

Cardiovascular/Drug Interactions

Gumweed may decrease the effects of some drugs that lower blood pressure because it may increase blood pressure; consult with a qualified healthcare professional, including a pharmacist, as dosing may need monitoring. Beyond this, no known interactions with other ingredients are reported in available phytotherapy references.

Renal Considerations

The volatile oils in Grindelia may have irritant effects upon the kidneys, suggesting that high-dose or prolonged internal use warrants caution in individuals with pre-existing renal impairment. This is a pharmacological inference from the volatile oil profile rather than a finding from clinical studies.

9. Geographic and Regulatory Status

Four Grindelia species serve as parent plants for the pharmaceutical drug Grindelia herba: G. robusta, G. camporum, G. humilis, and G. squarrosa; in California, G. robusta has been valued as a remedy since the 18th century, and in American naturopathy G. robusta serves as the parent plant of Herba Grindeliae, which is official in the USA. Gumweed was officially recognized in the Pharmacopoeia of the United States from 1882 to 1926. In the European Union, Grindelia preparations hold traditional herbal medicinal product status under the EMA's Committee on Herbal Medicinal Products (HMPC), with the approved indication being the relief of cough associated with the common cold based on traditional use alone.

10. Summary of Evidence Quality

The overall evidence profile for Grindelia/gumweed can be characterized as follows:

• Respiratory (expectorant/antitussive/anti-inflammatory): Supported by centuries of documented traditional use across multiple cultures and formal recognition in major pharmacopoeial and phytotherapy bodies (Commission E, ESCOP, EMA HMPC, European Pharmacopoeia, historical U.S. Pharmacopoeia). Mechanistic support exists from in vitro cell-culture studies (NF-κB pathway, cytokine inhibition, neutrophil modulation). No randomized controlled clinical trials have been published. Evidence grade: Traditional use / preclinical mechanistic support only.
• Dermatological (contact dermatitis, topical wound use): Supported by consistent traditional documentation across Native American cultures and one published case report with a noted conflict of interest. Evidence grade: Anecdotal/very weak clinical.
• Antimicrobial: Inconsistent in vitro results; no human studies. Evidence grade: Preliminary in vitro only.
• Immunomodulatory: Emerging in vitro data on neutrophil function; no clinical studies. Evidence grade: Preliminary in vitro only.

More evidence is needed to rate the effectiveness of gumweed for all currently studied uses.

References

• Gierlikowska B, Filipek A, Gierlikowski W, et al. Grindelia squarrosa Extract and Grindelic Acid Modulate Pro-inflammatory Functions of Respiratory Epithelium and Human Macrophages. Front Pharmacol. 2021;11:534111. PMC/PubMed
• Gierlikowska B, Gierlikowski W, Bekier K, et al. Inula helenium and Grindelia squarrosa as a source of compounds with anti-inflammatory activity in human neutrophils and cultured human respiratory epithelium. J Ethnopharmacol. 2020;249:112311. PubMed
• Schepetkin IA, Özek G, Özek T, et al. Neutrophil Immunomodulatory Activity of (−)-Borneol, a Major Component of Essential Oils Extracted from Grindelia squarrosa. Molecules. 2022;27(15):4897. PMC
• Essential Oil Composition of Grindelia squarrosa from Southern Idaho. PubMed (2023)
• Canavan D, Yarnell E. Successful treatment of poison oak dermatitis treated with Grindelia spp. (Gumweed). J Altern Complement Med. 2005;11(4):709-710. PubMed
• Kreutzer S, Schimmer O, Waibel R. Triterpenoid sapogenins in the genus Grindelia. Planta Med. 1990;56(4):392-394. PubMed
• ESCOP. Grindeliae herba (Grindelia). ESCOP Monograph 2015. European Scientific Cooperative on Phytotherapy
• Altmeyer's Encyclopedia of Dermatology / Phytotherapy: Grindeliae herba entry
• Altmeyer's Encyclopedia: Grindelia herba dosage and safety
• USDA NRCS Plant Guide: Great Valley Gumweed (Grindelia camporum)
• USDA NRCS Plant Guide: Curlycup Gumweed (Grindelia squarrosa)
• MSD Veterinary Manual: Selenium Toxicosis in Animals (Grindelia spp. as facultative selenium accumulators)
• Wikipedia: Grindelia camporum
• Wikipedia: Grindelia squarrosa
• WebMD Natural Medicines: Gumweed monograph (references compilation)
• RxList: Gumweed supplement monograph
• WholisticMatters: Gumweed / Grindelia robusta herb detail
• King's American Dispensatory (1898): Grindelia. Henriette's Herbal Homepage
• Essential Oil Composition of Grindelia squarrosa from Southern Idaho — Full Text, PMC 2023