Viola: Botanical Identity, Phytochemistry, Traditional Use, and Scientific Evidence
1. Identity and Botanical Classification
The genus Viola belongs to the family Violaceae. The genus Viola consists of approximately 500 species widely distributed throughout the world. In medicinal and supplement contexts, two species are of primary importance and are frequently studied together or used interchangeably:
- Viola odorata L. — commonly known as sweet violet or common violet. It is a small, fragrant perennial native to Europe and Asia, bearing characteristic dark-green, heart-shaped leaves and intensely scented purple to white flowers.
- Viola tricolor L. — commonly known as heartsease or wild pansy. Closely related subspecies include Viola arvensis Murray and Viola vulgaris. The herbal drug by definition consists of the dried flowering aerial parts of Viola arvensis Murray and/or Viola tricolor L.
Heartsease (Viola tricolor L.), a member of the Violaceae family, has a long history as a medicinal plant and has been documented in the Pharmacopoeia of Europe. The official pharmacopoeial herbal drug derived from this species is designated Violae herba cum flore (wild pansy herb with flower). It consists of the dried, flowering, above-ground parts of the wild pansy; quality is defined in the European Pharmacopoeia (Ph. Eur.).
The violet family consists of roughly 500 species across 20 genera, many of which are prevalent throughout diverse geographical regions. Viola tricolor blossoms in areas such as the Mediterranean, the Caucasus, and across continents including Europe, Asia, North and South America, and Australia.
1.1 Common Names
Viola odorata is known by many names across traditions: sweet violet (English), Banafsa (Sanskrit/Ayurvedic), Banafsaj (Arabic/Persian), and Zi Hua Di Ding (Traditional Chinese Medicine). Viola tricolor is known as heartsease, wild pansy, love-in-idleness, herb of the Trinity (Herba Trinitatis), and Johnny-jump-up, among others.
1.2 Common Preparations and Forms
Both species are encountered as dietary supplements and traditional herbal preparations in multiple forms:
- Dried herb / infusion (tea): Aerial flowering parts steeped in hot water.
- Hydroalcoholic (hydroethanolic) extract: The most common extract form used in modern pharmacological studies.
- Syrup: Flower or aerial-part extract prepared in a sweetened aqueous base; widely used in traditional Persian, Ayurvedic, and European herbal medicine for respiratory complaints.
- Fixed oil (violet oil): Flowers macerated in a carrier oil such as almond or sesame; used notably as nasal drops in Iranian traditional medicine for insomnia.
- Topical preparations: Creams, ointments, and bath additives prepared from the herb.
- Decoctions: Root and rhizome preparations used in some traditions.
Viola tricolor is a component of some prepared antitussives, cholagogues, dermatological medicines, roborants and tonics, alternatives, and anti-phlebitis remedies.
2. Traditional and Historical Use
2.1 Ancient Greece and Rome
It seems probable that V. odorata was a plant known and referred to by the ancient Greek pastoral poet Theocritus (c. 300–c. 260 BC). Both Genders (1971) and Grigson (1987) state that in ancient times V. odorata was in commercial cultivation for the sweetening properties of its perfume. By the Middle Ages, sweet violet was in use for culinary, medicinal, cosmetic, and perfumery purposes.
2.2 Medieval and Renaissance Europe
The traditional use of wild pansy goes back to ancient times. Wild pansy preparations were used during the Middle Ages mainly as a remedy for various skin ailments and were mentioned, according to Madaus (1938), by Lonicerus 1564; Hieronimus Bock 1565, Matthiolus (1501–1577). Viola tricolor has been used for more than thirty years in the European Community, mainly as a remedy for various skin ailments, especially those of a seborrheal nature. A syrup made of the flowers has been used to treat eye inflammation, sleeplessness, jaundice, coughs, bronchial ailments, and throat pain.
2.3 Traditional Persian Medicine (TPM)
Medicinal applications of V. odorata and respective products were derived from credible pharmaceutical textbooks of TPM (10th–18th century AD). Management of cough, fever, common cold, headache, insomnia, epilepsy, constipation, palpitation, dyspnea, dysuria, and skin diseases is among the most cited applications of V. odorata in TPM. In medieval Persia, powder of violet flowers appeared in Avicenna's Canon of Medicine to ease bronchitis.
2.4 Ayurvedic and South Asian Traditions
V. odorata appears to be well known in several medicinal systems (Iranian, Greco-Arab, Ayurvedic, and Unani) for treatment of whooping cough, headaches, migraine, insomnia, sore throat, and epilepsy in children and adults. In Ayurveda, the plant was used under the Sanskrit name Banafsa. Ayurvedic tradition typically uses the flowers and rhizomes — the blooms for syrups and aromatic oils, the roots for decoctions.
2.5 Traditional Chinese Medicine
In Traditional Chinese Medicine (TCM), Viola species — principally the aerial parts — are employed under the name Zi Hua Di Ding. The family Violaceae includes important medicinal herbs mentioned in traditional medicine for a variety of therapeutic applications, including purification of blood and the treatment of bruises and ulcers; in the Chinese system of medicine, it is recommended for use against cancer disorders.
2.6 Broader Ethnomedicinal Use
The main uses of V. odorata for respiratory problems are mentioned in different schools of traditional medicine such as traditional Chinese medicine, Ayurveda, and TPM. Likewise, the effects of violet are cited in various western herbal sources including the British Herbal Pharmacopoeia, European Pharmacopoeia, and the Physician's Desk Reference, where it is focused on as an expectorant and antitussive agent for bronchial catarrh.
In Iranian medicine, violet oil is traditionally used to treat insomnia. The oil is made using almond or sesame oil with V. odorata and is administered via nasal drops.
3. Key Chemical Constituents and Active Compounds
The genus Viola is highly rich in different natural products, of which about 200 compounds have been isolated and identified in the past few decades; these include flavonoids, coumarins, alkaloids, triterpenoids, saponins, anthocyanins, phenols, tannins, phytosterols, terpenoids, lignans, sesquiterpenes, cyclotides, and phenylpropanoids of different pharmacological activities such as antibacterial, antioxidant, anti-inflammatory, and antihypertensive effects, among others.
There are currently 370 compounds that have been isolated from the genus Viola, and the structure types include flavonoids, coumarins, alkaloids, lignans, sesquiterpenes, terpenoids, phytosterols, fatty acids, phenolic acids, cyclotides, and other compounds. Among these, cyclotides and flavonoids are the two types of compounds with more species isolated from the genus, and cyclotides are also one of the characteristic components of plants from the genus Viola. Coumarins and flavonoids are two types of compounds with high content in this genus.
3.1 Cyclotides
Cyclotides are the most structurally distinctive and pharmacologically diverse constituents of Viola. Cyclotides are a unique class of naturally occurring peptides characterized by a knotted arrangement of three disulfide bonds known as a cyclic cystine knot. This unique structural feature provides them with remarkable stability against proteolytic, chemical, and thermal degradation. About 30 cyclotides are identified from the aerial parts and roots of Viola odorata, 13 of which are novel sequences.
In several studies, cyclotides showed numerous biological activities such as uterotonic, hemolytic, anti-tumor, anti-HIV, cytotoxic, immunosuppressant, antiviral, and antimicrobial effects.
The immunosuppressive mechanism of cyclotides has been clarified by in vitro research: bioassay-guided fractionation and phytochemical analysis of aqueous Viola extract led to identification of cyclotides as bioactive components. An aqueous Viola extract contains bioactive cyclotides, which inhibit proliferation of activated lymphocytes in an IL-2 dependent manner. The findings provide a rationale for use of herbal Viola preparations in the therapy of disorders related to an overactive immune system.
3.2 Flavonoids
Among compounds in the genus, flavonoids and coumarins are the two types with higher content, and cyclotides are the most diverse compounds. Flavonoids, coumarins, and cyclotides from the genus Viola are also the leading research objects. In Viola tricolor, the principal flavonoids include rutin, violanthin, vitexin, violaquercetin, and anthocyanidin glycosides. Flavonoids (calculated according to violanthin; the highest content is found in the flowers), anthocyanins, and vitexin are present, as well as essential oils, salicylic acid methyl ester, mucilage, carotenoids, violaxanthin, and sugars.
In V. odorata, the flavonoid profile includes luteolin, kaempferol, apigenin, and quercetin. The extract used in research contains several flavonoids, including luteolin, kaempferol, apigenin, and quercetin. This reinforces the hypothesis that flavonoid and cyclotide contents of V. odorata may be responsible for its antitumor effect.
3.3 Saponins and Mucilage
Saponins are found across Viola species, particularly concentrated in the roots. Beyond the expectorant and antitussive activity of saponins and mucilages, the authors suggested that inhibition of total immunoglobulin E and reduction of interleukin (IL)-4 and IL-13 levels can be proposed as mechanisms of action of violet. The mucilage content of V. tricolor is notable, estimated at approximately 10% of the dry herb.
3.4 Salicylates and Phenolic Acids
Different groups of compounds have been isolated from various species of this genus, including cyclotide alkaloids, flavonoids, caffeic acid derivatives, salicylic acid, and triterpenoids. The presence of salicylate derivatives is believed to contribute to the anti-inflammatory properties attributed to Viola preparations.
3.5 Alkaloids and Additional Constituents
Viola odorata contains an alkaloid, glycoside, saponins, methyl salicylate, mucilage, and vitamin C. Additionally, aqueous preparations of V. odorata flowering tops revealed the presence of anthocyanins. Analysis of essential oil from the leaves revealed the presence of 25 identified compounds, representing 92.77% of the oil.
4. Pharmacological Mechanisms of Action
The pharmacological effects of Viola are attributed to several distinct mechanisms linked to its major compound classes:
4.1 Anti-Inflammatory Mechanisms
Studies have demonstrated that Viola tricolor has anti-inflammatory effects via inhibition of T-helper type 2 (Th2) cytokine production. Evidence has shown that Viola extract exerts numerous IL-2 biologic and degranulating effects, probably due to the multifunctional cyclotide components, although it did not display an effect on IL-2 receptor expression. The cyclotide-mediated immunosuppression appears to operate specifically through lymphocyte proliferation inhibition without altering receptor expression.
4.2 Antioxidant Activity
Previous studies indicated that Viola tricolor and Viola odorata are rich sources of antioxidants. Results showed that V. tricolor and V. odorata protect neuronal cells against serum/glucose deprivation-induced cell death, at least in part, by their antioxidant activities.
4.3 Cytotoxic and Anticancer Mechanisms
Cycloviolacin O2 (CyO2), a cyclotide from Viola odorata, has antitumor effects and causes cell death by membrane permeabilization. Interestingly, CyO2 did not produce significant membrane disruption in primary human brain endothelial cells, which suggested cyclotide specificity toward induced pore formation in highly proliferating tumor cells.
V. odorata extract significantly inhibited cell proliferation, but not vasculature in tumors, as revealed by immunohistochemical analysis for Ki-67 and CD31 expression, respectively. The extract increased the Bax/Bcl-2 ratio, suggesting induction of apoptotic pathways.
4.4 Antimicrobial Mechanisms
Cycloviolacin O2 is a cyclotide with potent activity against Gram-negative bacteria. The charged residues in CyO2 are all required for optimum antibacterial activity. Time-killing kinetic assays revealed that cyclotides at a concentration of 4 MICs achieved completely bactericidal effects within 2 hours, and fluorescence staining experiments confirmed that cyclotides disrupt microbial membranes.
4.5 Respiratory Mechanisms
A better understanding of the mechanism of action of Viola odorata in the treatment of inflammatory conditions of the lung has been made possible by recent animal studies. In an animal-model study that evaluated the prophylactic and therapeutic roles of violet in the treatment of formalin-induced lung damage, both aqueous extract of Viola flower and hydrocortisone significantly and similarly reduced hemorrhage area, alveolar wall thickness, alveolar septum rupture, and epithelial lining alteration of bronchioles.
5. Scientific Evidence by Area of Use
5.1 Insomnia and Sleep Quality
This is among the best-studied clinical applications of V. odorata in human trials.
Systematic Review and Meta-Analysis: A systematic review and meta-analysis was performed to assess the effect of V. odorata extract in the treatment of insomnia. PubMed, EMBASE, and Cochrane Library databases were searched. Four articles with five clinical trials including 224 patients were included in the analysis. The results indicated a greater improvement in total PSQI scores (MD, −4.67; P = 0.0002), subjective sleep quality score (MD, −0.91; P = 0.003), sleep duration score (MD, −0.77; P < 0.00001), and ISI score (MD, −6.30; P = 0.009) in the Viola extract group compared with the placebo group. However, the Viola extract group did not significantly differ in sleep latency (MD, −0.85; P = 0.08), habitual sleep efficiency (MD, −0.61; P = 0.21), sleep disturbances (MD, −0.36; P = 0.11), and daytime dysfunction (MD, −0.94; P = 0.12) from the placebo group.
Individual Trials: One study was conducted as an experimental pretest-posttest evaluation on V. odorata oil (VO) efficacy in 50 patients with chronic insomnia at an Iranian Traditional Medicine Clinic. Treatment consisted of intranasal drops of VO — two drops containing 66 mg of VO in each nostril, nightly before sleeping for one month. Improvements in sleep and ISI scores were significantly greater in patients after one month of VO drop compared with before starting treatment (P < 0.05).
A randomized clinical trial by Hejazian et al. investigated the effects of V. odorata oil nasal drops on sleep quality in the elderly using the PSQI, and revealed significant improvements in sleep quality, increases in sleep duration, reductions in sleep disorders, and improvement of delays in falling asleep.
ISI scores decreased from 16.32 ± 3.755 at baseline to 12.58 ± 3.592 and 6.48 ± 4.306 after 15 and 30 days of treatment, respectively. This suggests that the response to the treatment increases over time, unlike benzodiazepines, which cause drug resistance after their consumption.
Evidence Strength: Preliminary to moderate. The meta-analysis included only five small clinical trials (total n = 224). Outcomes were mixed — significant improvement was found in some sleep metrics but not others. Larger, rigorously controlled trials are needed before definitive conclusions can be drawn.
5.2 Respiratory Health: Cough, Bronchitis, and Upper Respiratory Infections
Viola tricolor L. as a traditional medical herb could suppress activated T lymphocytes and has been used empirically for asthma remedy. The anti-inflammatory effect of Viola tricolor and its underlying mechanism on asthma characteristics induced by ovalbumin (OVA) in mice has been investigated. The study demonstrated that Viola tricolor has anti-inflammatory effects via inhibition of T-helper type 2 (Th2) cytokine production and validated its empirical usage in traditional medicine. This is animal/in vitro evidence; clinical human evidence remains limited.
Clinical Trial (COVID-19/Respiratory Infection): Although all symptoms improved significantly in both groups, patients who received violet syrup recovered faster and the mean severity scores of cough (P = 0.025), myalgia (P = 0.036), headache (P = 0.037), and diarrhea (P = 0.044) decreased to a greater extent in comparison to the control group. This study — the first clinical trial on the effectiveness of Viola odorata on SARS-CoV-2 patients — showed that V. odorata effectively controlled prevalent manifestations of COVID-19 including cough, myalgia, headache, and diarrhea.
Modern clinical studies appear to confirm the efficacy of V. odorata syrup in cough, insomnia, and migraine as observed in traditional studies. V. odorata (as a syrup) appears to be a safe treatment for management of respiratory ailments in children. The efficacy of V. odorata in treatment of pain, fever, cough, infection, and inflammation may make it a suitable treatment for respiratory ailments. Larger clinical studies are required to confirm the effectiveness of V. odorata as an acceptable treatment for respiratory-related problems in children and adults.
Evidence Strength: Preliminary. The existing human trials are few and small. The COVID-19 trial was a single controlled study. Animal and in vitro data are more extensive and consistently support anti-inflammatory and antitussive activity, but these do not substitute for robust human clinical evidence.
5.3 Skin Disorders
This is the best-established traditional and regulatory-recognized indication for Viola tricolor (wild pansy / heartsease).
Due to its anti-inflammatory properties, Viola tricolor is regarded as a traditional remedy against skin diseases, for example for the treatment of scabs, itching, ulcers, eczema or psoriasis, and is also used in the treatment of inflammation of the lungs and chest such as bronchitis or asthma.
Its traditional use as herbal remedy is documented in several handbooks of phytotherapy, as well as in Anthroposophical Medicine, and is furthermore registered in the German Commission E Monograph of the German Federal Institute for Drugs and Medical Devices, as well as described in the Pharmacopoeia of Europe.
The ESCOP monograph lists indications for eczema, seborrhea, impetigo, acne, cradle cap, and diaper rash (internal and external). The German Commission E monograph endorses external use for mild seborrheic skin conditions and cradle cap.
In vitro experiments with wild pansy showed antibacterial and antioxidant activities; certain constituents exhibited cytotoxic activity against cancer cell lines. In vivo experiments in animals demonstrated anti-nociceptive, anti-inflammatory, and diuretic activities; in rats, improvement of induced eczema was described.
Evidence Strength: The evidence base for skin conditions relies predominantly on traditional use, regulatory recognition (Commission E, ESCOP, EMA HMPC), and preclinical/animal data. Formal human randomized controlled trials specifically for skin disorders are lacking, but the long history of use across multiple regulatory frameworks provides moderate indirect support.
5.4 Anticancer Activity
V. odorata extract (VOE) decreased cell viability of 4T1 breast cancer cells significantly. VOE significantly inhibited cell proliferation, but not vasculature in the tumors (as revealed by immunohistochemical analysis for Ki-67 and CD31 expression). VOE increased the Bax/Bcl-2 ratio in the VOE250-treated group compared to the control group, indicating promotion of apoptosis.
VOE at 250 mg/kg significantly decreased the metastatic rate in liver and lung compared to the other doses. Viola odorata has cytotoxic effects on 4T1 cells and affects antioxidant activity and metastasis in breast cancer. This is animal (murine) research only.
In the breast cancer cell line MCF-7 and its drug-resistant subline MCF-7/ADR, the cytotoxic effects of CyO2 (0.2–10 μM) were monitored in the presence and absence of doxorubicin using cell proliferation assays. SYTOX Green assays were performed to verify membrane permeabilization and showed cellular disruption correlates with cyclotide chemosensitization. Fluorescence microscopy studies demonstrated increased cellular internalization of doxorubicin in drug-resistant cells when coexposed to CyO2.
Evidence Strength: Preliminary — in vitro and animal data only. There are no human clinical trials evaluating Viola extracts or cyclotides for cancer treatment or prevention. These findings are mechanistically interesting and may inform drug development, but no clinical conclusions can be drawn.
5.5 Antimicrobial Activity
Cycloviolacin O2 is a cyclotide with potent activity against Gram-negative bacteria. Cyclotides from Iranian V. odorata have potent antimicrobial activity against Gram-negative, plant pathogenic bacteria.
Previously published studies have shown that extracts of V. odorata exhibit antibacterial activity against respiratory pathogens, specifically Streptococcus pneumoniae.
Evidence Strength: Preliminary — entirely in vitro. No human trials have assessed Viola as an antimicrobial agent.
5.6 Neuroprotection
Studies aimed to determine whether V. tricolor and V. odorata protect neurons against serum/glucose deprivation (SGD)-induced cell death in an in vitro model of ischemia and neurodegeneration. PC12 neuronal cells were pretreated for 4 hours with 1–50 µg/ml of V. odorata or V. tricolor hydroalcoholic extracts, followed by 24-hour incubation under SGD conditions. Results showed that V. tricolor and V. odorata protect neuronal cells against SGD-induced cell death, at least in part, by their antioxidant activities.
Evidence Strength: Preliminary — in vitro only. No human trials exist on neuroprotection.
5.7 Analgesic and Sedative Effects
Animal studies have been used to evaluate the neurological effects (such as presedative and sedative) of Viola. A chloroform-methanolic (70:30) extract of Viola demonstrated a higher presedative and sedative effect than diazepam, the reference drug. The analgesic effect of aqueous and methanolic extract of V. odorata in rats employing the tail immersion test and hot plate test showed significant effectiveness in peripheral and central models of pain.
Evidence Strength: Preliminary — animal data only. No controlled human analgesic trials are available.
5.8 Immunomodulation
An aqueous Viola extract contains bioactive cyclotides that inhibit proliferation of activated lymphocytes in an IL-2-dependent manner. The findings provide a rationale for use of herbal Viola preparations in the therapy of disorders related to an overactive immune system. However, further studies to evaluate clinical potency and potential risks have to be performed.
The immunosuppressive properties as well as the side effects of V. tricolor in a low-immunity individual need to be assessed.
Evidence Strength: Preliminary — in vitro mechanistic data. Clinically unexplored.
6. Body Systems and Health Areas Associated with Viola
Many plant species of this genus have received scientific validation of their pharmacological activities including neuroprotective, immunomodulatory, anticancer, antihypertensive, antidyslipidemic, analgesic, antipyretic, diuretic, anti-inflammatory, anthelmintic, and antioxidant effects. The primary body systems engaged by Viola include:
- Respiratory system: Antitussive, expectorant, and anti-inflammatory effects on bronchial and pulmonary tissue.
- Integumentary (skin) system: Anti-inflammatory and mild antiseptic activity applicable to eczema, seborrhea, acne, and diaper rash — the primary regulatory-recognized indication in Europe.
- Nervous system / Sleep: Sedative properties in animal models; human data for insomnia management (nasal violet oil).
- Immune system: Cyclotide-mediated lymphocyte suppression; potential immunomodulatory applications.
- Cardiovascular system: Antihypertensive and antidyslipidemic properties reported in preclinical work.
- Gastrointestinal system: Mild laxative, diuretic, and cholagogue effects documented historically and supported by some preclinical studies.
- Oncology (preclinical only): In vitro and animal-model evidence for cytotoxic and anti-metastatic activity.
7. Dosage Forms and Reported Dosages
The following dosages are drawn directly from authoritative sources and study reports:
7.1 Viola tricolor (Wild Pansy / Heartsease)
- External use — comminuted herb: infusum 1.5 g per cup of water, 3 times daily.
- Infusion for oral use: 5–10 g of comminuted herbal substance per 1 litre of boiling water. Use 1 dessert spoon 3 times daily.
- Cutaneous use: For topical use, 4 g of herb per 150 ml of boiling water, also for bath additive.
7.2 Viola odorata (Sweet Violet)
- Three times daily intake of 2–4 g of dried herb was recommended by the British Herbal Pharmacopoeia, and a 1 g daily dose of oral administration of root is noted in the Physician's Desk Reference (PDR).
- The recommended dosage of V. odorata is 2–5 g per day of dry flower.
- Viola odorata has been recommended by Iranian traditional medicine with a permissible maximum dose of 250 mg/kg, containing 20 g dry flower/dose, for the treatment of cough, rectal prolapse, and febrile convulsion in children.
- In the clinical trial for chronic insomnia, the treatment consisted of intranasal drops of violet oil — two drops containing 66 mg of VO in each nostril, nightly before sleeping for one month.
- A three-arm, double-blind, randomized trial was carried out to explore the effects of violet oil on 75 patients with chronic insomnia. Participants were randomly assigned to three groups: intranasal drops of violet oil, almond oil, or placebo (1% solution of carboxymethyl cellulose). Three drops were given at night before sleep for a period of 30 days.
8. Safety Considerations and Interactions
8.1 General Safety Profile
There are no observed health hazards or side effects at the appropriate therapeutic doses. A few patients in clinical trials reported some complications about V. odorata consumption, most of which were mild, and no serious adverse event was encountered. V. odorata was presented as a safe, well-tolerated, and effective herbal preparation in patients with chronic insomnia.
The drug is registered as a safe traditional antipyretic, antitussive, and anti-inflammatory agent for upper respiratory tracts by the Iranian Food and Drug Administration.
There are no reports about undesirable effects from wild pansy in the ESCOP review.
8.2 Overdose Risks
Gastroenteritis, vomiting, stomachache, nervousness, and depression may be observed when the recommended dose of 5–7 g is exceeded. Large doses of V. tricolor have the potential to cause gastrointestinal upset.
Large doses of V. tricolor have been known to cause nausea and vomiting in some individuals.
8.3 Salicylate Sensitivity
Those with a known hypersensitivity to salicylates should avoid using violets. The presence of salicylic acid derivatives and methyl salicylate in both V. odorata and V. tricolor is the basis of this concern.
8.4 Root vs. Aerial Parts
The roots of Viola species, which are particularly rich in saponins, carry a higher risk of adverse effects than the aerial flowering parts used in most preparations. The possible adverse effects may be due mainly to the high content of saponins of the root. V. odorata is considered a safe plant in the recommended doses and in healthy adults.
8.5 Pregnancy and Lactation
Clinical data on the interaction of sweet violet with supplements, as well as its effect on pregnancy and lactation, have not been established. Information on use during pregnancy and breastfeeding is currently not clear. In the absence of safety data, the use of Viola preparations beyond food amounts during pregnancy and breastfeeding is uncharacterized.
8.6 Immunosuppressive Potential
Given the in vitro demonstration of cyclotide-mediated lymphocyte suppression, there is a theoretical concern about the use of high-dose or concentrated Viola preparations in immunocompromised individuals. The immunosuppressive properties as well as the side effects of V. tricolor in a low-immunity individual need to be assessed.
8.7 Drug Interactions
No drug interactions are currently known for Viola preparations. However, given the salicylate content and theoretical immunosuppressive activity of cyclotides, caution is warranted when combining high-dose preparations with anticoagulant or immunosuppressive pharmaceutical agents. This interaction profile has not been formally evaluated in human studies.
8.8 Regulatory and Pharmacopoeial Status
The traditional use of Viola tricolor as a herbal remedy is documented in the German Commission E Monograph of the German Federal Institute for Drugs and Medical Devices, as well as in the European Pharmacopoeia (EP, 2011). Aqueous Viola tricolor extracts are traditionally applied topically for mild forms of inflammatory skin diseases, and these indications are in line with both the German Commission E Monograph and the European Pharmacopoeia. The EMA's Committee on Herbal Medicinal Products (HMPC) has also published a community herbal monograph covering Viola tricolor.
9. Overall Evidence Summary and Research Gaps
The pharmacokinetics and clinical studies on this genus are lacking. The pharmacological activity of plants from this genus mainly includes antibacterial, antiviral, antioxidation, anti-inflammatory, antitumour, neuroprotective, and hepatoprotective activity and others. There have been many research articles on the phytochemistry and pharmacological effects of plants from the genus Viola in recent decades.
Across all areas, the evidence hierarchy for Viola is as follows:
- Best clinical evidence: Insomnia (multiple small RCTs; one systematic review/meta-analysis with 224 patients) and respiratory infections/cough (small RCTs including a COVID-19 add-on trial).
- Regulatory/traditional recognition: Skin conditions (eczema, seborrhea, cradle cap), supported by European Commission E, ESCOP, and EMA HMPC monographs on the basis of long-standing traditional use.
- In vitro and animal evidence only: Anticancer, antimicrobial, neuroprotective, antihypertensive, and analgesic activities — these findings are mechanistically plausible but cannot be translated directly to clinical recommendations without human trial data.
Larger clinical studies are required to confirm the effectiveness of V. odorata as an acceptable treatment for respiratory-related problems in children and adults.
References
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