Alkanet

Alkanet (Alkanna tinctoria): A Comprehensive Reference

1. Identity: Botanical Classification, Names, and Forms

Scientific and Common Names

Alkanna tinctoria (L.) Tausch, commonly known as dyer's alkanet or simply alkanet, is a herbaceous flowering plant in the borage family Boraginaceae. The plant is also known as dyers' bugloss, orchanet, Spanish bugloss, or Languedoc bugloss. In Indian traditions it is widely referred to as ratanjot (Hindi/Urdu). Other synonyms encountered in older literature include Anchusa tinctoria, Racine d'alcanna, Racine d'orcanette, Radix anchusea, and Schminkwurzel (German).

The plant's name derives from the Greek anchousa, meaning "paint," underscoring its longstanding role in coloring practices.

Botanical Description and Natural Range

Alkanna tinctoria (L.) Tausch is a European perennial flowering plant of the Boraginaceae family. A hardy perennial, A. tinctoria thrives in dry, rocky soils and Mediterranean climates, growing up to 50 cm tall, with hairy, lance-shaped leaves and small blue-purple flowers. The root is blackish outside, blue-red inside, with a whitish core.

A. tinctoria is a medicinal plant common in Southern Europe (including Bulgaria), Northern Africa, and Southwestern Asia. It grows in dry, sunny grasslands in the lowlands. The Bulgarian populations are strongly fragmented and isolated from each other, and the species is included in the Red Book of the Republic of Bulgaria in the category "endangered." Alkanna is protected by the Biodiversity Act in Bulgaria, and its collection from the Bulgarian population is not allowed. Some localities are within sites of the European ecological network Natura 2000.

Although widely available in India, A. tinctoria naturally grows in the foothills of northern India and is also imported from Afghanistan.

Commercial Forms and Preparations

Alkanet root is commercially available in several forms used in various industries:

• Dried and powdered root: Used for oil infusions and dye baths in textiles and natural cosmetics.
• Oil infusions: The dyestuff in its roots is insoluble in water but can be extracted using alcohol or other organic solvents such as oils, making oil-based infusions the predominant extraction method for cosmetics.
• Topical ointments and creams: Formulations combining root of A. tinctoria with Vaseline, beeswax, and sesame oil have been used in clinical studies (see Section 5).
• Food colorant (E103/alkannin): In Australia, alkannin is approved for use as a food colouring; in the European Union, it is called E103 but its approval for use has been withdrawn.
• Wood stain: Powdered and mixed with oil, the alkanet root is used as a wood stain. When mixed into an oily environment, it imparts a crimson color to the oil, which when applied to wood moves the wood's color towards dark-red-brown, resembling that of rosewood, and accentuates the grain of the wood.
• Cosmetic colorant: It has been used as a colorant for products such as lipstick.

Alkanet contains at least two primary pigments, neither of which are water-soluble and both of which change color with pH. With the proper extraction and dyebath methods it can produce beautiful lavender and periwinkle blue colors; without the right adjustments it can also produce muddy browns. In alkaline environments, alkanet dye is blue; in the presence of acids it gradually changes to crimson.

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2. Traditional and Historical Use

Ancient Greek and Roman Medicine

Alkanet is an ancient dye that was used for thousands of years in the Mediterranean region; archaeologists have found recipes for it written on papyrus scrolls. Hippocrates recommended using alkanet roots to treat ulcers as early as the 5th century B.C. Alkanna tinctoria was well-known to the ancient Greeks and Romans, who referred to it as "alkanet." Dioscorides, the 1st-century physician, mentioned it in his pharmacopeia for treating skin afflictions and dyeing wool.

Ancient Romans employed the dye to color fatty cosmetics, sweets, and wines, enhancing their aesthetic appeal in daily life and trade.

Medieval and Early Modern Europe

During the 17th century, French women used ointments infused with alkanet to color their faces, though the tint was noted to fade rapidly, highlighting its role in ephemeral beauty rituals. Artisans also mixed the powdered root with oil to stain wood like mahogany and marble in flesh tones, contributing to decorative arts and furniture making.

It was historically used to colour some cheeses and low-quality wines. The root produces a fine red colouring material, which has been used as a dye in the Mediterranean region since antiquity.

Unani and Greco-Arabic Medicine

In Unani medicine, alkanet held repute as a cooling agent and was blended into topical formulations for boils, inflammation, and ulcers. While Alkanna is not one of the top-tier herbs in classical Ayurvedic texts, it appears in later Rasashastra and regional Ayurvedic formulations—particularly those influenced by Greco-Arabic exchanges during medieval trade. In Rajasthan and parts of Gujarat, folk practitioners applied "ratanjot" (its Hindi name) in oil blends for burns and skin infections.

South Asian and Traditional Indian Use

The well-known Kashmiri meal Rogan Josh gets its distinctive burgundy color from the use of alkanet root, which is also referred to by its other name, Ratanjot, in traditional Indian cuisine. It is traditionally infused in oils to provide the characteristic deep red shade to Kashmiri dishes such as Rogan Josh, symbolizing richness and authenticity in regional cuisine.

Oral and Topical Medicinal Uses Across Traditions

Today, alkanna root is used almost exclusively as a cosmetic dye. Orally, it has been used for diarrhea and gastric ulcers. Traditionally, topical alkanna root has been used to treat skin wounds and diseases. The plant has been utilized in various traditional medical practices for centuries for healing skin conditions, wounds, and inflammatory ailments.

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3. Key Constituents and Active Compounds

Primary Naphthoquinone Pigments: Alkannin and Shikonin

Alkanet roots contain two powerful naphthoquinone compounds (relatives of the anthraquinones found in plants like madder)—alkannin and shikonin. Alkannin and shikonin are enantiomers, mirror images of each other at the molecular level, and both are potent dyestuffs that can produce a range of violet and blue shades.

The IUPAC name of shikonin (C₁₆H₁₆O₅) is 5,8-dihydroxy-2-[(1R)-1-hydroxy-4-methyl-3-pentenyl]-1,4-naphthoquinone, determined by Brockmann and Liebigs in 1936, who further determined the enantiomer of shikonin, named alkannin. Shikonin (the R-enantiomer) exists as an enantiomeric pair with alkannin (the S-enantiomer), hence known collectively as A/S, and shows various pharmacological activities.

Alkanna root contains a mixture of red pigments found in the bark at levels of up to 5% to 6%. These consist mainly of fat-soluble naphthazarin (5,8-dihydroxy-1,4-naphthaquinone) components, such as alkannin and related esters.

The derivatives of alkannin include mainly acetylalkannin, propionylalkannin, isobutylalkannin, angelylalkannin, isovalerylalkannin, α-methyl-n-butylalkannin, β-hydroxy-isovalerylalkannin, and β,β-dimethylacrylalkannin, as well as others. It took almost 14 years to identify the accurate structure of shikonin (reported in 1936 by Brockmann); subsequently, its enantiomer alkannin was identified by the same group. Approximately 35 derivatives of alkannin and shikonin have been isolated from various plants of the Boraginaceae family and extensively investigated for a wide range of biological activities including wound healing, antimicrobial, anti-acne, antiulcer, anti-inflammatory, and anticancer activities.

Flavonoids and Polyphenols

Other constituents include flavonoids like luteolin and apigenin, which offer antioxidant effects. Tannins and rosmarinic acid have also been identified in the root extracts, contributing to its astringency and healing support. A. tinctoria is a traditional source of numerous bioactive metabolites such as naphthoquinones (especially alkannin and shikonin), flavonoids, polyphenols, and tannins, which are responsible for its pharmacological actions.

Phytosterols and Fatty Acids

Alkanet root contains alkannin and shikonin, both of which are pigments purported to be wound-healing and anti-inflammatory. It also contains phytosterols (beta-sitosterol, stigmasterol), and fatty acids (palmitic, stearic, and oleic).

Pyrrolizidine Alkaloids (PAs)

A. tinctoria also accumulates pyrrolizidine alkaloids (PAs), of which 7-angoylretronecin, triangularin, and dihydroxytriangularine have already been identified. Three pyrrolizidine alkaloids were isolated from Alkanna tinctoria and their structures analysed by spectroscopic methods; one of them is new and the name dihydroxytriangularine is proposed for it. These PAs represent the primary safety concern associated with the plant (see Section 7).

Shikonin Derivatives Identified by LC-MS

LC-MS has identified shikonin derivatives including p-hydroxybenzoic acid, β,β-dimethylacrylshikonin, mono- and diglycosylated shikonin, acetylated shikonin glycoside, and polyphenol-shikonin hybrids, known for their pharmacological activities.

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4. Mechanisms of Action

Antioxidant and Free Radical Scavenging

Alkannin and shikonin, two natural products from Alkanna tinctoria and Lithospermum erythrorhizon (Boraginaceae), are used in folk medicine where they are claimed to possess wound-healing and anti-inflammatory activity. A published investigation studied their in vitro antioxidant and hydroxyl radical scavenging activity as well as their in vivo anti-inflammatory activity. It was found that all examined compounds significantly inhibited in vitro lipid peroxidation of rat hepatic microsomal membranes, competed with DMSO for free hydroxyl radicals, and reduced inflammation (mouse paw edema induced by FCA) very efficiently. The examined compounds proved equal or superior to the common reference compounds for each of these properties. It was concluded that the claimed and/or proven actions of alkannin and shikonin are attributable at least partly to their intervention in free radical processes.

In a 2025 Chemistry Research Journal study, the ethanolic extract demonstrated potent antioxidant activity, demonstrated by DPPH (88.98% inhibition, IC₅₀ = 196.8 µg/mL), hydrogen peroxide scavenging, and diverse bioactive constituents including shikonin derivatives and polyphenols.

Anti-inflammatory Pathways

Shikonin's anti-inflammatory capacity is attributed to the regulation of immune cells, signaling pathways (e.g., TLR4/MyD88/NF-κB), and pro-inflammatory cytokines (e.g., TNF-α, IL-6). The regulation of these processes thereby enhances anti-inflammatory responses in target organs and mitigates autoimmune diseases.

Shikonin treatment significantly inhibited the expression of p-P65 and nuclear translocation of P65, and NF-κB pathway inhibitor PDTC significantly enhanced the anti-inflammatory and antiapoptotic effects of shikonin. Shikonin was found to significantly inhibit the inflammatory response and apoptosis of human primary nucleus pulposus cells, possibly through the NF-κB pathway.

Wound Healing

Shikonin has the pharmacological effect of promoting wound healing when used as a topical treatment in traditional Chinese medicine: its effect on skin repair is particularly prominent, and it is often made into a paste or infused oil. β-acetoxyisovaleryl alkannin (AAN-II), a derivative, promotes ulcer healing by inhibiting the inflammatory response and promoting fibroblast proliferation and angiogenic factor secretion. One proposed mechanism is the inhibition of bacterial growth in wounds while simultaneously promoting fibroblast activity—crucial in tissue regeneration.

Anticancer Mechanisms

Shikonin exerts antitumor effects by inducing multiple cell death modalities through caspase-3 activation, ROS generation, modulation of ATF3 expression, modulation of RIP1/RIP3 signaling, and activation of the BAX/caspase-3/GSDME pyroptosis axis. Furthermore, it suppresses tumor cell proliferation, inhibits metastasis, and blocks cell cycle progression by downregulating oncogenic c-Myc and MMP2 while upregulating the cell cycle inhibitor P21.

The cytotoxic actions of shikonin are largely through enhancing reactive oxygen species (ROS) generation to trigger caspase-dependent apoptosis and to downregulate nuclear factor-kappa B (NF-κB). Shikonin has a beneficial feature that it can induce apoptosis in many cancer cells despite its relatively low toxicity to normal cells.

Antimicrobial Mechanisms

Shikonin caused complete (100%) inhibition, and alkannin caused partial (79%) inhibition of wild-type E. coli ATP synthase. Both caused partial (4%–27%) inhibition of ATP synthase with genetically modified phytochemical binding site. This inhibition of bacterial ATP synthase provides a mechanistic basis for the observed antibacterial effects. Mechanistic action of shikonin and its derivatives has been documented against Staphylococcus aureus, Candida albicans, and Streptococcus pneumoniae, where ROS generation and mitochondrial membrane potential disruption play key roles.

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5. Scientific Evidence by Area of Use

5.1 Wound Healing

Human/Clinical Evidence: The most significant clinical study on alkanet as a therapeutic agent is a prospective, randomized, placebo-controlled trial published in BMC Complementary and Alternative Medicine (2017). The trial was conducted to compare the healing effectiveness of Alkanna tinctoria (L.) Tausch (Boraginaceae) with standard dressing on wound healing at the donor site after removal of a skin graft. Enrolled patients were randomly allocated to receive topical A. tinctoria extract ointment (20%) or standard dressing (dressing with base ointment) daily. Wound healing was assessed using the Bates-Jensen assessment tool at the 2nd and 4th weeks after intervention.

Decreases in wound score were significantly greater in the A. tinctoria group compared with the placebo group (P <0.05). The surface areas of graft donor sites in the A. tinctoria group were significantly reduced as compared with the control group at day 28 of the intervention (P <0.05). The trial treated 60 patients with Alkanna tinctoria Tausch extracts dressing and base ointment as a placebo. They observed 50% and 96.66% of patients with complete wound healing within 2 to 4 weeks respectively in the treated group; 0% and 23.3% respectively in placebo groups—a statistically significant difference.

Limitations: The study was a single center trial with a relatively small sample. Patients with diabetes, renal failure, liver failure, cancer, malnutrition, and age over 60 were excluded, limiting generalizability. No long-term follow-up was reported.

Animal/Pre-clinical Evidence: Shikonin/shikonin dimers isolated from bark extracts had wound-healing-promoting effects on incisional wounds in albino rats. During the second wound healing process in dogs, the side of the tissue treated with enantiomeric naphthoquinone alkannin and shikonin (A/S) ointment had a significantly higher mean LDF value and higher collagen and epithelial thickness score compared to the effects of treatment with Ringer's solution of lactic acid.

Histological findings pointed to the ability of the ointment to promote angiogenesis, collagen production, and epithelialization of lesions, although the time to complete wound closure was not significantly higher than in the control group. These results contradict those of previous human clinical trials, which had demonstrated the compound's efficacy in clinical cases of chronic, severe, or contaminated wounds.

Histoplastin red ointment, well known for its wound-healing benefits, contains alkannin esters.

Evidence strength: Moderate for topical wound healing; supported by one positive randomized controlled trial (RCT) in humans and multiple preclinical studies. Larger, multi-center RCTs are needed to confirm findings.

5.2 Antimicrobial Activity

Pre-clinical/In Vitro Evidence: An investigation evaluated the biological potential of A. tinctoria leaves extract against multidrug resistant human pathogenic bacteria including Acinetobacter baumannii, Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. Anti-multidrug-resistant bacterial activity of aqueous, chloroform, ethanol and hexane extracts of Alkanna tinctoria leaves was evaluated by well diffusion method. Among the four extracts of Alkanna tinctoria leaves, aqueous extract showed best activity against A. baumannii (10 ± 03 mm), P. aeruginosa (12 ± 0.5 mm), and S. aureus (14 ± 0.5 mm) as compared to Imipenem.

A separate study examined the antimicrobial activity of alkanet root extracts (methanol, ethanol, and acetonitrile) against 9 clinical microorganisms. Alkanet root extracts showed antimicrobial activity against 2 (Proteus spp. and S. haemolyticus) out of 9 microorganisms.

Shikonin, a naphthoquinone compound, has favorable biological activities such as anti-inflammatory, antibacterial, immunomodulatory, anticancer, and wound-healing-promoting pharmacological activities.

Evidence strength: Preliminary; restricted to in vitro studies. No controlled human trials for antimicrobial applications have been conducted.

5.3 Antioxidant Activity

Alkanna root has demonstrated radical scavenging activity, suggesting potential anti-aging effects; however, clinical trial information is lacking. Extracts from alkanet roots have applications as natural food coloring agents and have demonstrated proven antioxidant effects in laboratory settings. Alkanet root extracts showed antioxidant, sun protection, anti-wrinkle, and antimicrobial effects.

Evidence strength: Preliminary; limited to in vitro assays and animal models. No human clinical trials specifically investigating antioxidant outcomes have been published.

5.4 Anticancer Properties

Alkannin/shikonin (A/S) and their derivatives are naturally occurring naphthoquinones. They are integral constituents of traditional Chinese medicine Zicao (roots of Lithospermum erythrorhizon). In the last two decades, significant increase in pharmacological investigations on alkannin/shikonin and their derivatives has been reported, resulting in the discovery of novel mechanisms in various diseases and disorders.

In an in vitro study towards CMT-U27 cancer cells, acetonitrile root extract at 100 µg/mL concentration showed strong and significant anti-proliferative effect.

Shikonin enhances chemosensitivity via β-catenin modulation and inhibits PD-L1 expression through the NF-κB/STAT3 and NF-κB/CSN5 pathways, mediating tumor immunomodulation as a result.

Evidence strength: Exclusively preclinical (cell culture and animal models). No human clinical trials on alkanet-derived compounds for cancer treatment have been reported. Research on the closely related enantiomer shikonin from Lithospermum erythrorhizon provides mechanistic context but cannot be directly extrapolated to clinical outcomes with A. tinctoria.

5.5 Gastrointestinal Applications

Alkanna root was traditionally used topically for the treatment of skin wounds and diseases. Orally, alkanna root has been used for diarrhea and gastric ulcers. Antiulcer activity has been investigated and documented in the broader literature on alkannin/shikonin derivatives.

Evidence strength: Based exclusively on traditional use reports and preclinical data. No human clinical trials supporting oral use for gastrointestinal conditions have been identified.

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6. Body Systems and Health Areas

• Integumentary system (skin and wound healing): The most-studied biomedical application; supported by one human RCT and multiple preclinical studies in wound closure, re-epithelialization, angiogenesis, and collagen synthesis.
• Immune and inflammatory system: The chiral compounds A/S are potent pharmaceutical substances with a wide spectrum of biological and pharmacological activities including wound healing, antimicrobial, anti-inflammatory, anticancer, and antioxidant activity.
• Oncology (investigational): Multiple in vitro and animal studies point to activity across various cancer cell lines, primarily via ROS/apoptosis/NF-κB pathways; no human data available.
• Gastrointestinal tract: Traditional oral use for diarrhea and gastric ulcers; no clinical data.
• Cosmeceutical / Skin aging: Recent innovations in drug delivery systems, such as chitosan-based nanoparticles and electrospun nanofibers, have enhanced the efficacy of A. tinctoria extracts in wound healing applications. The plant also shows promise in cosmeceuticals due to its UV-protective and anti-aging properties.
• Food preservation: Due to their antioxidant and antibacterial activity, alkanet extracts display significant preservative effects and could be promising preservative additives in the production of functional foods, e.g., meat products, alkannin-enriched yogurt, and even sweets and beverages with enhanced color and flavor.

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7. Dosage Forms and Dosages Reported in Studies

No recent clinical data justify human dosage recommendations for oral use. The following dosages have been used specifically in published studies:

• Topical ointment (wound healing, human RCT): Topical A. tinctoria extract ointment at a concentration of 20%, applied daily, was used in the Kheiri et al. (2017) trial in split-thickness skin graft donor sites.
• In vitro (anticancer): Acetonitrile root extract at 100 µg/mL concentration showed anti-proliferative effects against a canine mammary carcinoma cell line in vitro.
• In vitro (antioxidant): The ethanolic extract exhibited 88.98% DPPH radical inhibition at 1000 µg/mL (IC₅₀ = 196.8 µg/mL).
• Cosmetic use (safety limit): The Cosmetic Ingredient Review (CIR) Expert Panel has recommended alkanet root as safe when used at ≤2% concentration in finished cosmetic products.
• Preclinical (anti-inflammatory, shikonin): An intraperitoneal injection of shikonin at 20 mg/kg for 21 days was used in a C57BL/6 experimental autoimmune encephalomyelitis (EAE) mouse model examining shikonin's role in neuroinflammation.

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8. Safety Considerations and Drug Interactions

Pyrrolizidine Alkaloids: The Primary Hazard

Alkanet root contains pyrrolizidine alkaloids (PAs), compounds known for hepatotoxicity (causing liver damage) when used in high doses and over prolonged exposure. The types of toxicity caused by these alkaloids in both animals and humans include hepatotoxicity, pneumotoxicity, and genotoxicity.

Alkanna root may cause acute liver failure, cirrhosis, pneumonitis, pulmonary hypertension, or heart failure. Alkanna root may cause hepatic and/or lung toxicity because of the pyrrolizidine alkaloid components. Toxic byproducts from the hepatic metabolism of pyrrolizidine alkaloids are transported to the lungs where they may cause additional systemic damage.

A 2014 study found PAs detected in the human blood stream after cosmetic use (Lachenmeier et al., Journal of Toxicology).

Regulatory Status

In Australia, alkannin is approved for use as a food colouring; in the European Union, it is called E103 but its approval for use has been withdrawn. It is also not listed in the FDA's list of food colours approved in the USA.

A. tinctoria accumulates pyrrolizidine alkaloids (PAs), and these can be co-extracted with other constituents, meaning the use of extracts in the food industry can be restricted.

Topical Use and Broken Skin

There is significant concern about using alkanna as medicine because it naturally contains harmful chemicals called pyrrolizidine alkaloids (PAs). These chemicals can harm the liver. Applying alkanna preparations that contain these chemicals to broken skin is likely unsafe.

Because alkanet is a natural product, the PA content can vary depending on growing location, growing conditions, and processing; some manufacturers use PA-free extracts or purification methods to reduce risks. If products meet certain purity standards, they can be labeled "hepatotoxic PA-free." However, there is not enough information to know whether it is safe to use "hepatotoxic PA-free" preparations during pregnancy or breastfeeding.

Pregnancy and Liver Disease

Alkanna preparations that contain hepatotoxic pyrrolizidine alkaloids (PAs) might cause birth defects as well as liver damage during pregnancy. Alkanna contains chemicals called hepatotoxic pyrrolizidine alkaloids (PAs). These chemicals harm the liver, making existing liver disease worse.

Drug Interactions

The pyrrolizidine alkaloid components of alkanna root are substrates for the cytochrome P450 3A4 isoenzyme. Inducers of this isoenzyme, including rifampin, St. John's wort, and phenobarbital, may increase the conversion of pyrrolizidine alkaloids to toxic metabolites. Medications that cause the liver to break down alkanna might enhance the toxic effects of chemicals contained in alkanna. Some of these medicines include carbamazepine (Tegretol), phenobarbital, phenytoin (Dilantin), rifampin, rifabutin (Mycobutin), and others.

Variability in PA Content and Conservation

Potential toxicity concerns, particularly related to pyrrolizidine alkaloids, highlight the need for rigorous safety assessments. Additionally, the variability in phytochemical composition due to environmental factors or extraction methods underscores the importance of standardized protocols.

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9. Research Gaps and Status

Pharmacological assessment on a large scale and clinical trials are essential to validate the centuries-old claims and regulate herbal products made from the plant. Despite a rich preclinical research landscape, the body of human clinical trial data for A. tinctoria remains very limited. In the last two decades, significant increase in pharmacological investigations on alkannin/shikonin and their derivatives has been reported, resulting in the discovery of their novel mechanisms in various diseases and disorders, but this work has yet to translate to registered human therapies. The regulatory withdrawal of alkannin as a food colorant (E103) in the EU and its absence from FDA-approved food color lists reflect continued uncertainty surrounding its systemic safety profile.

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References

• Kheiri A, et al. (2017). The effects of Alkanna tinctoria Tausch on split-thickness skin graft donor site management: a randomized, blinded placebo-controlled trial. BMC Complementary and Alternative Medicine, 17:253.
• Khan UA, et al. (2015). Alkanna tinctoria leaves extracts: a prospective remedy against multidrug resistant human pathogenic bacteria. BMC Complementary and Alternative Medicine, 15:127. PMC4410581.
• Pharmacological and analytical aspects of alkannin/shikonin and their derivatives: An update from 2008 to 2022. PMC9669360.
• Pharmacological Effects of Shikonin and Its Potential in Skin Repair: A Review. PMC10745356.
• Metabolite Production in Alkanna tinctoria Links Plant Development with the Recruitment of Individual Members of Microbiome Thriving at the Root-Soil Interface. PMC9601132.
• Shikonin protects against lipopolysaccharide-induced inflammation and apoptosis in human nucleus pulposus cells through the NF-κB pathway. PMC8497831.
• Shikonin Induces Apoptosis, Necrosis, and Premature Senescence of Human A549 Lung Cancer Cells through Upregulation of p53 Expression. PMC4337265.
• Comparison of the Potential of "Green" Classical and Natural Deep Eutectic Solvents in the Production of Natural Food Colorant Extracts from the Roots of Alkanna tinctoria (L.). PMC11854224.
• Alkannin and shikonin: effect on free radical processes and on inflammation—a preliminary pharmacochemical investigation. PubMed PMID 12210768.
• Shikonin and Alkannin inhibit ATP synthase and impede the cell growth in Escherichia coli. PubMed PMID 37758110.
• Pharmacological and analytical aspects of alkannin/shikonin and their derivatives: An update from 2008 to 2022. PubMed PMID 36405061.
• Recent Advances of Shikonin in the Molecular Mechanisms of Anticancer, Anti-Inflammation and Immunoregulation. PubMed PMID 40582725.
• Review of Shikonin and Derivatives: Isolation, Chemistry, Biosynthesis, Pharmacology and Toxicology. Frontiers in Pharmacology, 2022.
• Pyrrolizidine alkaloids from Alkanna tinctoria. Phytochemistry. ScienceDirect.
• Drugs.com: Alkanna Root Uses, Benefits & Dosage. Medically reviewed Oct 24, 2025.
• Wikipedia: Alkanna tinctoria.
• Rai A, et al. (2025). Phytochemical and pharmacological investigation of Alkanna tinctoria. Chemistry Research Journal, 10(4):75–82.
• Alkanna Species: A Promising Herbal Medicine and its Uses. ResearchGate/Fortune Journals, 2019.
• Antimicrobial Activity and Cytotoxicity of Alkanna tinctoria (L.) Tausch Root Extracts. The Black Sea Journal of Sciences.
• Antibacterial activity of an aqueous extract of Alkanna tinctoria roots against drug resistant aerobic pathogenic bacteria isolated from patients with burns infections. Russian Open Medical Journal, 2018.