Tragacanth (Gum Tragacanth): A Comprehensive Reference
1. Identity: Botanical and Chemical Classification
1.1 Botanical Source and Nomenclature
The principal botanical source of tragacanth is Astragalus gummifer Labill. The stems and branches of Astragalus gummifer, Astragalus gossypinus, and Astragalus microcephalus are the species from which the gum is produced as exudate in dried form. Astragalus gummifer is a spiny shrub belonging to the family Fabaceae. Generally, gum tragacanth (also known as Katira) is sourced from Central Asia and Eastern countries, and Iran is the largest producer and exporter of this natural gum.
The name "tragacanth" derives from the Greek words tragos (goat) and akantha (thorn), referring to the thorny plants goats graze on. Common names for the substance include goat's thorn, green dragon, gum dragon, gum tragacanth, gummi tragacanthae, hog gum, milkvetch, and Syrian tragacanth. In South Asia, the gum is known as Gond Katira or Kathila.
Gum tragacanth holds the food additive E number E413. Its CAS Registry Number is 9000-65-1.
1.2 Harvesting and Physical Forms
Gum tragacanth is gathered after sap seeps from Astragalus tree wounds and hardens into curled ribbons or flakes; the main source of gum is the massive tap roots of the plant, each of which contains a center cylinder of gum. The gummosis process, which is triggered by mechanical or biological damage, produces the gum physiologically; the soft gum is secreted and soon dries on the trunk in response to injury to a stem or root.
Structurally, there are two general types of gum tragacanth: ribbon (the best grades) and flake (or harmony). It is 1–3 cm long, has a width of at least 0.5 cm, and is in the form of pale white or yellowish color strips. In commerce it is also available as a fine powder. The gum is odorless, tasteless, and swells upon soaking in water.
1.3 Chemical Identity
Tragacanth gum is a plant-derived molecule obtained from the stems and branches of Asiatic species of Astragalus, having a molecular weight of about 840 kDa. It is a branched and anionic carbohydrate composed of a complex mixture of polysaccharides, and is thus very heterogeneous in its structure.
It consists mainly of two fractions: water-soluble (tragacanthin, 50–75%) and water-swellable (bassorin, 25–50%). The water-soluble tragacanthin is reported as a neutral, highly branched arabinogalactan (type II) comprising a (1–6) and (1–3)-linked core chain containing galactose and arabinose (both in furanose and pyranose forms) and side groups of (1–2), (1–3), and (1–5)-linked arabinose units occurring as monosaccharides or oligosaccharides. The easy separation of tragacanthin and bassorin suggests that the two polysaccharides exist as a physical mixture and are not chemically bonded.
Tragacanth is composed of polysaccharides containing D-galacturonic acid, D-galactose, L-fucose, D-xylose, L-arabinose, and L-rhamnose; the galacturonic acid is found principally in the polymer backbone structure, with the other five monosaccharides also in the side chains. The exudate also contains metal cations including potassium, calcium, and magnesium, and a small amount of protein.
Because of seasonal and geographical variations, commercial tragacanth obtained from different species exhibits large differences in chemical composition, including sugar composition, methoxy content, and the relative proportion of soluble and insoluble components. In most Astragalus species, the bassorin and tragacanthin have also been found to contain methyl groups, probably representing methoxylated galacturonic acid; the insoluble bassorin part generally appears to have less methoxyl substitutions than the soluble fraction.
2. Traditional and Historical Use
2.1 Ancient Mediterranean and Middle Eastern Records
Gum tragacanth is one of the most ancient gums of commerce, being described by Theophrastus in the third century BC. Tragacanth has been known from a very early period: Theophrastus in the 3rd century BC mentioned Crete, the Peloponnesus, and Media as its native countries; Dioscorides, who as a native of south-eastern Asia Minor was probably familiar with the plant, describes it correctly as a low spiny bush.
Historically, tragacanth has been used for centuries, with evidence suggesting its use in ancient Persia and the Middle East; it was traded along the Silk Road and eventually made its way to Europe. This gum has been valued since ancient times, especially in Persia and Greece, where it was used medicinally for coughs, burns, and digestive issues.
2.2 Ayurvedic and Unani Medicine
Historically, gond katira (tragacanth) was extensively utilized in traditional medicine across ancient Persia and India, originating primarily in the mountainous regions of Iran and neighboring Middle Eastern countries, where it became a valued commodity along historical trade routes. Traditional communities utilized it for cooling beverages, sweets, and herbal remedies to relieve digestive and heat-related conditions; classical Ayurvedic texts such as the Bhavaprakasha Nighantu and Charaka Samhita highlight gond katira as a cooling ("Sheetala") substance that effectively balances Pitta Dosha.
In Iranian traditional medicine, tragacanth is used as a demulcent for treating sore throat and hair loss due to seborrhea. Historically, it has been used in the treatment of respiratory, digestive, and metabolic disorders; the gum is highly prized in Ayurveda, Unani, and other folk systems for its soothing and rejuvenating qualities.
2.3 Traditional Galenical and European Pharmacy
Historically, tragacanth has been taken by mouth to treat digestive complaints and coughing; it has also been used in small amounts as a laxative because it swells up and becomes slick as it is exposed to fluids in the stomach and intestines, and the resulting soft, slippery mass may help to relieve constipation by triggering intestinal muscle contractions. In larger doses, tragacanth's ability to absorb excess water and add bulk to intestinal contents may be moderately effective for treating diarrhea.
In the past, tragacanth was added to cough syrups and lozenges because of its soothing effect on irritated mouth and throat tissue. Powders using tragacanth as a basis were sometimes called diatragacanth; as a mucilage or paste, it has been used as a topical treatment for burns.
In powder form, gum tragacanth was used as a vehicle for active and heavy medicines, for the purpose of giving cohesion and firmness to lozenges, and to form pastes used in pharmaceutical compounding. Traditional Galenic formulas recorded in historical European pharmacy include "Tragacanth Cooling Powder" (Diatragacanth Frigidum), troches for cough, and electuaries — composite preparations used for respiratory and urinary complaints, as documented in early modern apothecary texts attributed to Galen, Mesue, and Nicholas.
3. Key Constituents and Mechanisms of Action
3.1 Polysaccharide Fractions
When gum tragacanth is mixed with water, only the soluble fraction (tragacanthin) dissolves to give a colloidal hydrosol, whereas the insoluble fraction swells to a gel; chemically, tragacanthin is a complex mixture of acidic polysaccharides. The gum's thickening and stabilizing properties are attributed to its complex branched structure, which allows it to interact with water molecules and form a viscous solution or gel.
3.2 Demulcent and Mucosal-Coating Mechanism
Tragacanthin, a key chemical component of Astragalus gummifer, is primarily responsible for its demulcent properties; as a water-soluble polysaccharide, it dissolves to form a viscous colloidal solution that coats and soothes irritated mucous membranes; this soothing action is especially beneficial in managing burning sensations within the gastrointestinal or respiratory tracts.
3.3 Dietary Fiber Mechanisms
Tragacanth (E 413) is unlikely to be absorbed intact and is partially fermented by intestinal microbiota. There is evidence that certain high molecular weight dietary polysaccharides such as gums could be partially broken down in the large intestine of man. As a soluble dietary fiber, tragacanth's physicochemical properties — particularly its high viscosity — underlie its proposed gastrointestinal and metabolic effects. A thicker meal environment can slow gastric emptying and slow carbohydrate absorption, which may reduce sharp post-meal glucose spikes for some people.
Research comparing plant exudate gums (including Arabic gum and tragacanth gum) and guar gum with bile salts found that ITC measurements do not evidence specific interactions between gums and the studied bile salts, so that their cholesterol-lowering ability, if any, is due to a different mechanism very probably bound to the viscosity increase.
3.4 Immunomodulatory Properties
Polysaccharides from gum tragacanth have been reported to display potential biological activities including specific and non-specific immunomodulatory, antioxidant, anticoagulant, hypocholesterolemic, antiviral, anti-inflammatory, keratinocyte DNA repair, and antitumor properties — though not all polysaccharides exhibit all of these effects.
3.5 Antinociceptive Mechanism
The antinociceptive effect induced by gum tragacanth in the writhing test has been shown to be reversed by the systemic administration of yohimbine (an α₂-adrenergic antagonist), but not by naloxone, glibenclamide, or theophylline; the findings indicated that gum tragacanth induces its antinociceptive effect through the adrenergic system.
4. Scientific Evidence by Area of Use
4.1 Gastrointestinal Health
Traditional background: Tragacanth has been used across multiple traditional systems for constipation, diarrhea, and general digestive complaints.
Clinical/human evidence: Following a 7-day control period, 5 healthy men ingested 9.9 g tragacanth gum daily (3 × 3.3 g portions gelled in 200 ml water) for 32 days; measurements were made of blood glucose, insulin, serum lipids, haematological indices, and biochemical analyses, with 24-hour urine samples and 5-day faecal collections also collected. The ingestion of gum tragacanth had no discernible effects on plasma biochemistry (fifteen parameters), haematological indices (seven parameters), urinalysis (seven parameters), glucose tolerance, serum cholesterol, triglycerides, or phospholipids; the gum was well tolerated and none of the volunteers experienced any side effects or allergic reactions. The researchers noted faster intestinal transit and slightly higher fecal weight, changes considered normal physiological responses to increased fiber intake.
Evidence strength: The only published controlled human study involved just five volunteers and assessed safety and tolerability rather than therapeutic efficacy. Evidence for specific gastrointestinal therapeutic use in humans is preliminary and insufficient to make clinical recommendations.
4.2 Blood Glucose Modulation
Clinical/human evidence: Some preliminary evidence suggests that concomitant ingestion of tragacanth with a high sugar load can moderate glucose levels in patients with diabetes (Eastwood 1984); however, this effect has not been consistently demonstrated and more detailed investigations are needed (Eastwood 1986). Fibers other than guar, such as gum tragacanth and methylcellulose, reduced hyperglycemia to a lesser extent than guar gum, and the effects of bran and cholestyramine were unimpressive (Jenkins et al., 1978).
In research that looks at multiple gums, the strongest and most consistent effects on blood glucose are not usually attributed to tragacanth specifically; this does not mean tragacanth does nothing, but expectations should be kept modest unless it is used as part of a broader fiber strategy.
Evidence strength: Human evidence is limited and inconsistent. The mechanistic basis (viscosity-mediated slowing of glucose absorption) is plausible but not uniquely validated for tragacanth compared to other soluble fibers.
4.3 Blood Lipids (Cholesterol and Triglycerides)
Clinical/human evidence: Although gum tragacanth swells to increase stool weight and decrease gastrointestinal transit time, it differs from other soluble fibers in that it appears to have no effect on serum cholesterol, triglyceride, or phospholipid levels after a 21-day supplementation period (Eastwood 1986).
Animal data: In a comparative study of the hypocholesterolemic activity of various mucilaginous polysaccharides, tragacanth gum fed at a level of 3% along with 3% cholesterol in the diet of cockerels inhibited the development of hypercholesterolemia (Riccardi & Fahrenback, 1965).
Evidence strength: The one controlled human study found no lipid-lowering effect. Animal data show modest cholesterol-inhibiting effects under high dietary cholesterol loading conditions. There is no human clinical trial specifically designed to test a lipid-lowering hypothesis for tragacanth.
4.4 Antiviral Activity
Preclinical (animal) evidence: Tragacanthin polysaccharides from Astragalus brachycentrus (AV208) and Astragalus echidnaeformis (AV212) plants, which are devoid of in vitro antiviral activity, were evaluated in a mouse model of Punta Toro virus (PTV) infection — a phlebovirus used as a model for studying Rift Valley fever and hantavirus infections; single intraperitoneal treatments with 12.5–200 mg/kg/day doses of AV212 given 24 h before or 4 and 24 h after virus inoculation protected the majority of mice from mortality. The authors proposed that the protection was likely mediated through immunostimulation rather than direct antiviral action, as no direct in vitro antiviral activity was detected.
Evidence strength: This is animal (mouse) data only. No human trials exist for tragacanth as an antiviral agent.
4.5 Antinociceptive (Analgesic) Activity
Preclinical (animal) evidence: One published study investigated the antinociceptive effect of several concentrations (125, 250, and 500 μg/kg body weight) of Astragalus gummifer gum (AGG) on thermal and acetic acid-induced pain in mice. The percentage inhibition of acetic acid-induced writhing in AGG groups at 125, 250 and 500 μg/kg was 47%, 50%, and 54% vs. control, compared to 66.3% for the diclofenac sodium group. These data from the mouse study suggest that tragacanth may have analgesic effects via the blockade of alpha-2 adrenergic receptors.
Evidence strength: Preclinical (animal) only. No human data are available. The route of administration (intraperitoneal injection) used in the mouse study does not correspond to typical human use.
4.6 Wound Healing
Preclinical and limited clinical evidence: In a prior study, the use of tragacanth gum dressing bandages for treating burns led to swift and complete wound recovery; the outcomes were superior to those in the control group; in that study, a rat with full thickness wounds was treated with a solution of tragacanth gum twice a day for 10 days. In vitro scratch assays and small animal studies demonstrate enhanced wound closure rates and reduced bacterial load when compared with untreated control. Positive effects of tragacanth on wound healing were demonstrated in one small clinical trial.
Evidence strength: Predominantly preclinical. One small clinical trial has shown positive results, but the evidence base is insufficient to support clinical recommendations.
4.7 Immunomodulation
Preclinical evidence: Purified polysaccharide fractions from tragacanth gum have been identified as modulators of the immune system; the immune system of the host is reportedly stimulated or suppressed by such fractions to combat cancer cells, virus infections, or immunological disorders by natural means.
Evidence strength: The immunomodulatory evidence for tragacanth-specific fractions is predominantly in vitro and animal-based. There are no published human trials specifically assessing tragacanth's immune effects.
5. Body Systems and Health Areas
- Gastrointestinal system: Historically taken by mouth to treat digestive complaints and coughing; also used in small amounts as a laxative because it swells up and becomes slick as it is exposed to fluids in the stomach and intestines, and the resulting soft, slippery mass may help to relieve constipation by triggering intestinal muscle contractions.
- Respiratory system: In the past, tragacanth was added to cough syrups and lozenges because of its soothing effect on irritated mouth and throat tissue.
- Metabolic/endocrine system: Proposed influence on postprandial glucose via viscosity-mediated slowing of carbohydrate absorption; human evidence is weak and inconsistent.
- Immune system: Gum tragacanth contains non-specific immunomodulatory, hypocholesterolemic, anti-inflammatory, and antiviral effects. These are based on in vitro and animal data.
- Integumentary system (skin/wound healing): Gum tragacanth has the ability to both heal wounds and act as an antioxidant, making it a potential candidate for usage in wound dressings.
- Musculoskeletal/pain: Preliminary evidence from animal studies for analgesic activity mediated through the adrenergic system; no human data available.
6. Pharmaceutical and Formulation Applications
6.1 Pharmaceutical Excipient
The most frequent pharmaceutical application of gum tragacanth occurs as a suspending and emulsifying agent. Gum tragacanth is an effective suspending agent for many pharmaceutical products; it generally acts to suspend the active ingredient by increasing the viscosity of the external phase and thus prevents undissolved material from settling out; it is used in practice as a suspending agent in aqueous mixtures containing resinous tinctures and heavy insoluble powders.
It has proved its efficacy as a prospective biopolysaccharidic excipient as a binder, filler, matrix-former, and release retardant in various pharmaceutical tablets; gum tragacanth has extensively been used as an excipient in many kinds of drug delivery dosage forms including tablets, films, nanoparticles, microparticles, gels, hydrogels, and scaffolds.
Glycerite of tragacanth is a useful excipient to bind tablet masses; mucilage of tragacanth is used in lotions for external applications; it is also used at higher concentrations as a base for jelly lubricants; and an important use of gum tragacanth is in spermicidal jellies.
6.2 Minimum Quality Standards
Minimum quality and safety standards for gum tragacanth to be used in food and pharmaceutical products have been defined by the United States Pharmacopeia (USP 31), the EU, and JECFA.
6.3 Novel Drug Delivery Research
Gum tragacanth has emerged as an adaptable and promising biopolymer with diverse applications in food, pharmaceuticals, and cosmetics; its exceptional physicochemical properties, including strong acid resistance and stabilizing, emulsifying, and gelling abilities, have made it essential in various drug delivery systems. Through a study on gelation and mucoadhesion, it was discovered that tragacanth exhibits potential as an excipient for the oral administration of proteins and peptides, such as insulin; tragacanth's properties suggest that it could enhance the drug loading capacity, encapsulation efficiency, and stability of insulin encapsulated within tragacanth particles by utilizing ionic attraction between tragacanth and the amino groups of insulin's amino acid residues.
7. Dosage Forms and Reported Dosages
Recent clinical evidence does not support a specific therapeutic dosage of tragacanth. The dosages reported in the limited available scientific literature are as follows:
- Human safety study (Eastwood et al., 1984): Five healthy men ingested 9.9 g tragacanth gum daily (administered as 3 × 3.3 g portions gelled in 200 ml water) for 32 days following a 7-day control period. Oral daily intake of up to 9,900 mg tragacanth/person per day (approximately equivalent to 141 mg tragacanth/kg body weight per day) for up to 21 days was well tolerated in humans.
- Antiviral study in mice (Smee et al., 1996): Single intraperitoneal treatments with 12.5–200 mg/kg/day doses were used in the mouse Punta Toro virus model.
- Antinociceptive study in mice (Bagheri et al., 2015): Concentrations of 125, 250, and 500 μg/kg body weight of Astragalus gummifer gum were administered intraperitoneally in mice.
- Food additive context: Comparing the daily intake used in human safety testing to the levels of gum tragacanth anticipated to be consumed as a food additive, it became clear that the test dose was absurdly high compared to approximately two grams per person per year in the UK.
Tragacanth is used in pharmaceuticals and foods as an emulsifier, thickener, stabilizer, and texturant additive. In traditional South Asian use, tragacanth is soaked in water overnight and consumed as part of beverages or desserts; however, no standardized dose for this use has been established in peer-reviewed literature.
8. Safety Considerations
8.1 Regulatory Status
Tragacanth was affirmed as a GRAS (Generally Recognized As Safe) excipient in the USA in 1972 (FDA, 2014). The EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS) provided a scientific opinion re-evaluating the safety of tragacanth (E 413) as a food additive; in the EU, tragacanth was evaluated by the Scientific Committee for Food (SCF, 1989) and by JECFA (1987), who both allocated an acceptable daily intake (ADI) of "not specified" for this gum.
Tragacanth was evaluated by JECFA in 1969, 1973, 1977, 1980, 1983, and lastly in 1985; three toxicological monographs were prepared; based on the lack of adverse effects in the available toxicity database, an ADI "not specified" was allocated by JECFA.
8.2 Carcinogenicity and Genotoxicity
In a 96-week carcinogenicity study, tragacanth gum was administered at dietary levels of 0 (control), 1.25, and 5.0% to groups of 50 male and 50 female B6C3F1 mice; mean body weights of females in the higher dose groups were lower than those of controls; however, there were no treatment-related clinical signs or adverse effects on survival rate, urinalysis, haematology, blood biochemistry, or organ weight; while detailed histopathology revealed the development of squamous cell hyperplasias and papillomas in the forestomach, there was no significant treatment-related increase in the incidence of any preneoplastic or neoplastic lesion, and tragacanth gum was not carcinogenic in B6C3F1 mice of either sex.
Tragacanth (E 413) is unlikely to be absorbed intact and is partially fermented by intestinal microbiota; no adverse effects were reported in carcinogenicity studies at the highest dose tested and there is no concern with respect to genotoxicity.
8.3 Reproductive and Developmental Toxicity
Tragacanth gum fed to rats at dietary levels up to 6% had no effect on reproductive performance nor on post-partum development of the pups; the only effects observed in both the F0 and F1 generations were lower body weights and decreased feed-efficiency at the 6% level; since these effects were not accompanied by any compound-related histological changes in any tissues or organs, the effects may be due to the bulking effect of this non-nutritive substance rather than any innate toxicity.
Information regarding safety and efficacy in pregnancy and lactation in humans is lacking.
8.4 Allergic Reactions and Hypersensitivity
Allergic reactions to tragacanth are rare but documented; reported symptoms in sensitive individuals include bronchial asthma, hives, swelling under the skin, nasal congestion, and digestive problems; several of these cases involved people who were also allergic to pollens, suggesting possible cross-reactivity. EFSA noted that the proteins naturally present in tragacanth are the likely trigger for these hypersensitivity reactions and recommended that manufacturers reduce protein content as much as possible.
For tragacanth as an active ingredient, no authorized medicinal products exist within the EU; in the literature, it is pointed out that sensitization is possible, resulting in hypersensitivity.
8.5 Acute Toxicity
The oral LD₅₀ of tragacanth gum in hamsters has been reported as 8,800 mg/kg.
8.6 Drug and Preservative Interactions
Tragacanth gum has been shown to variously alter the bactericidal activities of preservatives and antibiotics; it significantly enhanced the antibacterial action of benzyl alcohol, whereas it reduced that of methylparaben, phenylmercuric nitrate, phenylmercuric acetate, phenol, merthiolate, benzalkonium chloride, aminosidin sulfate, neomycin, penicillin, streptomycin sulfate, and tetracycline hydrochloride. These interactions have been observed in pharmaceutical formulation research and are relevant to product development rather than typical dietary supplement consumption. No drug–nutrient or drug–supplement interactions are well documented in the clinical literature.
8.7 Gastrointestinal Tolerability
Some individuals report gastrointestinal discomfort (bloating, gas) following consumption. This is consistent with the fermentation of high molecular weight polysaccharides by intestinal microbiota, a property shared with other soluble dietary fibers.
8.8 Quality Variability
Problems associated with gum tragacanth standardization stem from the variation in rheological and chemical characteristics that change depending on the species used, and the geographical and seasonal characteristics and harvesting mode. Usage of tragacanth has declined due to high cost and variable quality; EFSA re-evaluated it in 2017 and maintained approval with no numerical ADI, noting limited toxicological data available but concluding no safety concern at current low usage levels.
References
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