Hyssop

Hyssop (Hyssopus officinalis L.): A Comprehensive Reference

1. Identity and Botanical Characterization

1.1 Nomenclature and Taxonomy

Hyssopus officinalis L. is a traditional medicinal plant that belongs to the family Lamiaceae. Its accepted scientific name is Hyssopus officinalis Linnaeus, and it is most commonly known by the vernacular names hyssop, garden hyssop, and common hyssop. The genus Hyssopus is widespread in central Asia, the East Mediterranean, and Mongolian areas. It has six main species which are used as herbal remedies, with Hyssopus officinalis being the most widely cultivated; the other five species are H. ambiguus, H. cuspidatus, H. latilabiatus, H. macranthus, and H. seravschanicus. In traditional Persian medicine, the plant is referred to as "Zufa yabis." The genus name derives from the ancient Greek hyssopos, which was later adopted into Latin as hyssopus.

1.2 Plant Description and Natural Source

Hyssop is a brightly coloured shrub or subshrub that ranges from 30 to 60 cm in height. The stem is woody at the base, from which grow a number of branches. The stems are 0.5–0.7 m in height, erect, or decumbent, dividing into many woody stems. The leaves are opposite, shiny dark-green, entire-edged, and lanceolate or oblong, obtuse to acuminate, that are 2–4 cm long and 0.5–1 cm wide. It is native to the Mediterranean basin, found growing wild in regions with temperate climates and dry soils. Its natural habitat includes hills, calcareous areas, roadsides, and sunny slopes, especially in southern Europe, extending to mountainous areas of the Iberian Peninsula, the Pyrenees, and parts of central Asia.

H. officinalis is today a well-established aromatic and medicinal plant around the world, whose pharmacological properties have been known since ancient times. Due to the high content of essential oils (0.3–1.0%), one of the most important species among Hyssopus is Hyssopus officinalis L., frequently used as a drug in the pharmaceutical industry and as a functional ingredient in the food industry.

1.3 Medicinal Part and Common Preparations

Hyssop is an herb prepared from the leaves and flowers of Hyssopus officinalis, and more broadly from the aerial parts of the plant, which is a member of the mint family indigenous to Southern Europe and the Middle East. Hyssop herb (Hyssopi herba) and its pharmaceutical preparations — including infusions, syrups, tinctures, and extracts — have been used in traditional medicine since ancient times.

Common modern preparations include:

• Hyssop extract is available as capsules and as liquid extracts.
• Herbal tea (infusion), prepared by steeping the dried aerial parts in hot water.
• Essential oil, obtained by steam distillation of the aerial parts, primarily used in aromatheapy, cosmetics, and food flavoring.
• A medicinal preparation of hyssop, so-called hyssop oxymel, is made from the fresh or dried herb, macerated in honey and some apple cider vinegar.
• Hyssop is also used to flavour liqueurs such as Chartreuse and Absinthe, providing the green colouring in many versions of the latter.

Its constituents, especially essential oils, are popularly used as an additive in beverages, foods, and cosmetics.

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2. Traditional and Historical Use

2.1 Ancient and Religious Use

Hyssop has been a well-known medical and culinary herb since ancient times. The plant is mentioned many times in the Bible as spiritually purifying. The name hyssop appears as a translation of the Hebrew word Ezov in some translations of the Bible, and refers to its use in ritual cleansing, "Purge me with Hyssop and I shall be clean"; however, researchers have suggested that it is not likely to be Hyssopus officinalis, which is not native to Palestine — rather it may have been a species of oregano or the caper plant.

The biblical phrase "purge me with Hyssop, and I shall be clean" echoes the ancient Greek use of this herb for cleansing sacred sites. Classical Greek authors including Dioscorides recommended it for reducing lung inflammation and treating respiratory ailments.

2.2 Persian and Medieval Medical Traditions

Avicenna (980–1037 AD), the outstanding Iranian philosopher and physician of medieval Persia, stated in the Canon of Medicine that the most common application of this plant is treating pulmonary diseases including asthma. The Canon of Medicine also listed hyssop among the herbs recommended for cough management. Hyssopus officinalis L. is included in Avicenna's listings of medicinal plants cited in the Canon of Medicine for cough management.

2.3 Indications Across Traditional Systems

Hyssopus officinalis has been used for centuries for various purposes including as a carminative, expectorant, and cough reliever, and it has been used for the treatment of numerous conditions such as ulcers, asthma, jaundice, leprosy, dropsy, bronchitis, COPD, diabetes, AIDS, and bacterial and fungal infections as an herbal remedy.

Hyssop herb and its pharmaceutical preparations have been used in traditional medicine since ancient times as antiseptic, carminative, diaphoretic, emmenagogue, expectorant, muscle relaxant, stomachic, and tonic agents.

A long list of different valuable therapeutic properties has been reported for hyssop extracts and essential oils, such as spasmolytic, antiviral, sudorific, emmenagogue, carminative, tonic, diuretic, expectorant, antiseptic, antibacterial, antioxidant, anti-inflammatory, and cardiovascular effects.

Hyssop has been used in folk medicine for centuries for stimulation of the circulation and for treatment of a variety of conditions including upper respiratory illness, asthma, cough, sore throat, intestinal infections, gastrointestinal upset, and gall bladder disease. Hyssop is also used topically in gargles, medicinal baths, and creams for skin irritation, burns, and frostbite.

In Iranian traditional medicine (ITM), hyssop (Hyssopus officinalis L.) is a well-known compound used for cold catarrh, pneumonia, cough, asthma, and other inflammatory lung diseases.

2.4 Culinary and Industrial Traditions

The leaves and young shoots can be eaten raw in salads or used as flavouring in soups and stews. Dried hyssop is sometimes used in the herb blend Za'atar. Bright and aromatic flowers of hyssop attract honeybees, and honey from these bees is of high quality: clear, golden in color, with a specific and very pleasant taste. Hyssopus officinalis could be cultivated as a honey herb.

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3. Phytochemistry: Key Constituents and Active Compounds

3.1 Essential Oil Composition

Essential oil is the most important and the most frequently investigated product of hyssop. Available literature data on wild and cultivated plants indicate that its herb yields 0.3–1% of essential oil, with isopinocamphone as the dominant compound, along with pinocamphone, β-pinene, 1,8-cineole, pinocarvone, linalool, sabinene, and methyl eugenol.

The most characteristic and important components in hyssop oils are isopinocamphone (syn. cis-,(3)-pinanone), pinocamphone (syn. trans-,(3)-pinanone), and their precursor β-pinene. Among other principal constituents are pinocarvone, sabinene, germacrene D, germacren D-4-ol, α- and β-phellandrene, 4-carvomenthenol, thymol, carvacrol, elemol, limonene, linalool, and 1,8-cineole.

The essential oil profile varies substantially by geographic origin and chemotype. Analysis of the var. decumbens form revealed linalool (49.6%), 1,8-cineole (13.3%), limonene (5.4%), β-caryophyllene (2.8%), β-pinene (3.0%), and α-pinene (2.4%); however, climate, environmental factors, species subtypes, and extraction methods can considerably affect the plant's essential oil profile. The Italian form contains pinocamphone and isopinocamphone (4.4% and 43.3%, respectively), whereas the French species do not; instead, linalool, 1,8-cineole, and limonene are predominant.

Major classes of chemical compounds found in H. officinalis essential oil are bicyclic monoterpenes, monoterpenoids, acyclic monoterpenes, phenolic monoterpenoids, monocyclic monoterpenes, monocyclic sesquiterpenes, tricyclic sesquiterpenes, bicyclic sesquiterpenes, tricyclic sesquiterpenoids, and straight-chain saturated hydrocarbons.

3.2 Polyphenolic Compounds

Of the different types of polyphenols in Hyssopus, the most abundant phenolic acids were ferulic acid (13.2 mg/100 g) and caffeic acid (6.5 mg/100 g). Three flavonoid glycosides — isoquercitrin, rutin, and quercitrin — and two flavonoid aglycones, quercetin and luteolin, were also found.

In methanol extracts, the most abundant phenolics were chlorogenic and rosmarinic acid (23.35–33.46 and 3.53–17.98 mg/g, respectively).

Beside the essential oil, hyssop herb contains flavonoids and phenolic acids, tannins, diterpene lactones (marrubiin), and triterpenoid compounds such as ursolic and oleanolic acid.

The plant contains up to 2% of a volatile oil primarily composed of pinocamphone, isopinocamphone, alpha- and beta-pinene, camphene, and alpha-terpinene. Other constituents of the plant include glycosides (hyssopin as well as the flavonoid glycosides hesperidin and diosmine), tannin 5% to 8%, oleanolic acid, ursolic acid, beta-sitosterol, marrubiin, and resins.

3.3 Chemotype Variability

The morphological and genetic hyssop complexity describes its high variability and the existence of numerous geographically different subspecies. This chemotypic diversity has important practical and pharmacological implications: preparations sourced from different regions may differ substantially in the relative proportions of pinocamphone (associated with convulsant risk) versus linalool- or 1,8-cineole-dominant oils (associated with lower neurological risk), which directly affects both therapeutic activity and safety.

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4. Established Mechanisms of Action

4.1 Spasmolytic / Muscle-Relaxant Mechanism

The muscle-relaxing activity of the essential oil of Hyssopus officinalis L. and some of its main components (isopinocamphone, limonene, and β-pinene) was studied on isolated preparations of guinea-pig and rabbit intestine. The essential oil and isopinocamphone inhibited the acetylcholine- and BaCl₂-induced contractions in guinea-pig ileum in a concentration-dependent manner (IC₅₀ 42.4 µg/ml and 61.9 µg/ml to acetylcholine; 48.3 µg/ml and 70.4 µg/ml to BaCl₂), whereas limonene or β-pinene left tissue contraction unchanged. In guinea-pig ileum, H. officinalis essential oil also blocked the contractions induced by CaCl₂. In isolated rabbit jejunum the essential oil reduced the amplitude of spontaneous movements and decreased basal tone; neither haemoglobin, methylene blue, N(omega)-nitro-L-arginine methyl ester (L-NAME), nor propranolol blocked the myorelaxant effect. These findings indicate a calcium-channel-antagonist-like spasmolytic mechanism for the essential oil, with isopinocamphone identified as an active principal.

4.2 Anti-inflammatory Mechanisms

Two dominant phenolic compounds in hyssop herb extracts were rosmarinic and caffeic acids. Rosmarinic and caffeic acids achieved strong interaction with COX-1 and COX-2 receptors in silico. This suggests that inhibition of cyclooxygenase enzymes may contribute to the anti-inflammatory activity attributed to hyssop extracts.

A study examined whether hyssop extract activated anti-viral innate immunity through activation of endosomal TLRs recognizing nucleic acids and their downstream signaling. The hyssop herb extract was prepared and co-cultured with healthy individuals' peripheral blood mononuclear cells (PBMCs); gene expression levels of TLR3, 7, 8, and 9, as well as MyD88 and NF-κB, were evaluated using real-time PCR. Secretion levels of immune-related cytokines were then quantified via ELISA. The hyssop-treated PBMCs demonstrated an elevated expression of endosomal TLR genes, as well as MyD88 and NF-κB. Moreover, the release of IFN-α and β notably enhanced in cell culture supernatant, while the content of inflammatory cytokines remarkably diminished.

4.3 Alpha-Glucosidase Inhibitory Mechanism

Alpha-glucosidase inhibitors, specifically (2S, 3S)1-O-beta-D-6'-O-cinnamoylglucopyranosyl-3-(3'',5''-dimethoxy-4''-hydroxyphenyl)-1,2,3-propanetriol and its glucoside analog, from the dry leaves of hyssop, were isolated. A study examined the alpha-glucosidase inhibitory effects of hyssop extracts on intestinal carbohydrate absorption in rat everted gut sac and carbohydrate-loaded hyperglycemia in mice. Oral pre-administration of hyssop extract significantly suppressed sucrose- and maltose-loaded hyperglycemia in mice and in vitro inhibited intestinal α-glucosidase activity. It was suggested that hyssop extracts inhibited the digestion of complex carbohydrates, but not that of absorbable monosaccharide, and might be a useful supplemental food for hyperglycemia.

4.4 Antiviral Mechanism (HIV — In Vitro)

A polysaccharide (MAR-10) was isolated from the aqueous extract of Hyssopus officinalis and examined for its activity against HIV-1 (SF strain) in HUT78 T cell line and primary cultures of peripheral blood mononuclear cells. MAR-10, in a concentration-dependent manner, inhibited HIV-1 replication as demonstrated by inhibition of HIV-1 p24 antigen and syncytia formation. Furthermore, MAR-10 had no significant direct toxicity or effect on lymphocyte functions or CD4+ and CD8+ T cell counts. MAR-10 was also found to have broad-spectrum anti-glycosidase activity.

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5. Scientific Evidence by Area of Use

5.1 Respiratory System: Asthma and Bronchospasm

Background: Various preparations of hyssop have been used medicinally for respiratory problems, including cough, chest congestion, sore throat, and bronchitis.

Human / Clinical Evidence: In a randomized triple-blind placebo-controlled trial, 60 mild-to-moderate asthmatic patients were randomized to receive either hyssop syrup (5 ml twice daily containing 6 g Hyssopus officinalis L. extract) or plain sugar syrup (5 ml twice daily) for 4 weeks as an adjuvant to routine treatment. Outcome measures were the Asthma Control Test (ACT), pulmonary function tests, Expert Panel Report 3 (EPR3), and wheezing severity. The patients with productive cough in the hyssop group showed significant improvement in forced expiratory volume in 1 second (FEV1), ACT (at the 4th week), peak expiratory flow (PEF), maximal expiratory flow rate 25–75% (MEF25–75%), and wheezing severity. The benefit was notably phenotype-specific — improving primarily in patients with productive (wet) cough — with no significant benefit seen in the non-productive cough subgroup.

Evidence Strength: This is a single small RCT (n = 60), and it was conducted as an adjuvant to routine asthma therapy, limiting conclusions about hyssop's standalone efficacy. The study is preliminary but is the strongest available clinical evidence for any indication of hyssop.

Mechanistic Support: The spasmolytic properties documented in ex vivo studies of isolated smooth muscle preparations (see Section 4.1) provide biologically plausible support for reported respiratory benefits. The main constituents of Hyssopus officinalis L. include polyphenolic compounds and essential oils generally known to have antimicrobial and antioxidant properties. Essential oils can also act as expectorants and antispasmodics.

5.2 Anti-inflammatory Activity

Preclinical Evidence: Dry methanol extracts of hyssop herb exhibited notable antioxidant activity in DPPH and FRAP assays. Methanol extracts expressed moderate to weak antioxidant activity (DPPH IC₅₀ = 56.04–199.89 µg/mL, FRAP = 0.667–0.959 mmol Fe²⁺/g).

Studies on hyssop have proved antimicrobial and antifungal effects against E. coli, P. aeruginosa, S. aureus, Staphylococcus pyogenes, and Candida albicans, and also anti-inflammatory effects.

Evidence Strength: Anti-inflammatory activity is supported predominantly by in vitro (cell culture and biochemical assay) and in silico studies involving COX-enzyme interaction modelling. No completed randomized human trials specifically targeting inflammation as a primary endpoint have been published. Evidence for anti-inflammatory activity in humans remains absent; all findings to date are preclinical.

5.3 Antiviral Activity

In Vitro Evidence: Antiviral activity against human immunodeficiency virus type 1 (SF strain) in HUT78 T cell line and primary cultures of peripheral blood mononuclear cells has been observed using an isolated polysaccharide extract from hyssop (MAR-10). There are currently no human studies on the whole plant extract.

The hyssop extract was capable of inducing antiviral innate immune responses, and so can be promising in antiviral drug strategies. However, this finding needs ongoing examinations on mechanisms by which the plant exerts anti-inflammatory consequences. A limitation of the study is the lack of a functional assay.

Evidence Strength: Some studies indicate that hyssop may possess potential antiviral properties, particularly against HIV and herpes simplex virus, though these findings primarily derive from cell-culture research and require further investigation in humans. Evidence remains entirely preclinical (in vitro / cell line). No human antiviral trials exist.

5.4 Antimicrobial and Antifungal Activity

Hyssop has moderate antioxidant and antimicrobial activity against Gram-positive and Gram-negative bacteria, together with antifungal and insecticidal and antiviral properties in vitro. These activities have been attributed to the volatile oil components, which disrupt microbial cell membranes, and to polyphenols including rosmarinic acid, which may inhibit microbial enzymes.

Evidence Strength: Entirely in vitro. No human clinical antimicrobial trials have been reported for hyssop as a primary intervention.

5.5 Antidiabetic / Alpha-Glucosidase Inhibition

A study examined the alpha-glucosidase inhibitory effects of hyssop extracts on intestinal carbohydrate absorption in a rat everted gut sac and carbohydrate-loaded hyperglycemia in mice. In the everted gut sac experiment, 10 mM sucrose- and 5 mM maltose-treated increases in glucose concentration in the serosal compartment were inhibited in the presence of 0.5 and 1.0 mg/mL hyssop extracts, although a 10 mM glucose-induced increase in serosal glucose was not inhibited by the extracts.

Animal model studies indicate myorelaxant, antiplatelet, and α-glucosidase inhibitory activities for this plant.

Evidence Strength: Preclinical only (animal models, in vitro gut preparations). No clinical trials in humans with diabetes or impaired glucose tolerance have been conducted with hyssop preparations.

5.6 Antioxidant Activity

Findings of available studies reveal that hyssop possesses valuable antioxidant properties for culinary and possible medicinal use. Antioxidant capacity has been measured by DPPH radical scavenging and FRAP assays in multiple extract types. The sample richest in chlorogenic and rosmarinic acids was also the richest in total polyphenols. The antioxidant capacity varies widely across preparation types and geographic sources.

Evidence Strength: Antioxidant activity is well characterized in vitro. Its translation into clinically meaningful human antioxidant effects has not been demonstrated in controlled trials.

5.7 Neurological: Seizure Models (Animal Data Only)

A study of extract of H. officinalis on seizures induced by pentylenetetrazole (PTZ) and hippocampus mRNA level of iNOS in rats found that 100 mg/kg dose of hyssop extract might have anticonvulsant effects. However, these anticonvulsant effects might not occur through the iNOS gene expression.

Evidence Strength: Animal data only. This area is complicated by the parallel evidence of convulsant risk from the essential oil at higher doses (see Section 7).

5.8 Overall Evidence Summary

Human studies, adverse reactions, and clinical trials examining the reported properties of hyssop are absent (beyond the single asthma RCT) and need more attention to determine whether biological differences in findings of studies reflect different isolation procedures, different types of plant material used, collection time, locations, or different chemotypes. The preponderance of evidence remains preclinical.

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6. Body Systems and Health Areas

• Respiratory System: The primary historically documented and experimentally explored area. Different properties of hyssop including antiviral, antispasmodic, antibacterial, antioxidant, antifungal, and immunomodulatory effects have been shown in previous studies relevant to respiratory conditions.
• Gastrointestinal System: Hyssop can stimulate the gastrointestinal system. Traditionally used as a carminative and antispasmodic; the spasmolytic mechanism on intestinal smooth muscle preparations has been established in preclinical studies.
• Immune System: In vitro evidence suggests modulation of innate immune signaling via TLR pathways and cytokine regulation.
• Endocrine / Metabolic System: Alpha-glucosidase inhibitory activity identified in animal and ex vivo models, pointing toward potential relevance for postprandial blood glucose regulation.
• Cardiovascular System: Hyssop is a peripheral vasodilator and promotes perspiration, thereby potentially cooling in feverish conditions. Diosmin, present in hyssop, has been studied for vasoprotective properties in other contexts.
• Nervous System: Dual and conflicting evidence: the whole-plant aqueous extract has shown anticonvulsant potential in animal models, while the concentrated essential oil (particularly pinocamphone-dominant chemotypes) is a recognized convulsant risk at sufficient doses.
• Skin: Topically used historically in gargles and creams for skin irritation; antimicrobial and antioxidant constituents provide a mechanistic rationale.

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7. Dosage Forms and Reported Dosages

The following dosages are reported from identified studies and established clinical or traditional sources; they are not recommendations.

• Asthma (clinical trial): In the published randomized trial, 5 ml of hyssop syrup twice daily, containing 6 g of Hyssopus officinalis L. extract, was administered for 4 weeks as an adjuvant to routine asthma treatment.
• Capsules / Liquid extract: Hyssop extract is available as capsules and as liquid extracts, and it is taken two to three times daily (as reported in product use documentation reviewed by NIH LiverTox).
• Animal seizure model: In a rat pentylenetetrazole model, hyssop extract was injected intraperitoneally at three doses — 50, 100, and 200 mg/kg — 15 minutes before seizure induction.
• In vitro (spasmolytic): The essential oil and isopinocamphone inhibited acetylcholine- and BaCl₂-induced contractions in guinea-pig ileum at IC₅₀ values of 42.4 µg/ml (essential oil to acetylcholine) and 61.9 µg/ml (isopinocamphone to acetylcholine).

No standardized pharmacopeial dosing guidelines from European Pharmacopoeia, WHO monographs, or Commission E are available in the literature reviewed for this article. The absence of a validated standardized extract and the wide variability in chemotype composition make dose standardization particularly challenging.

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8. Safety Considerations and Interactions

8.1 Convulsant Risk of the Essential Oil

The most clinically significant safety concern associated with hyssop is the convulsant potential of its concentrated essential oil. In rats, commercial preparations of hyssop essential oils produced convulsions at 0.13 g/kg and death at 1.25 g/kg. Case reports of seizures in adults and children exist. The neurotoxicity of hyssop appears to be related to two terpene ketones, pinocamphone and isopinocamphone; other monoterpenes with similar chemical structures, such as camphor, thujone, and cineole, are known to have epileptogenic properties.

The volatile oil, particularly its constituent pinocamphone, has been reported to cause seizures in laboratory animals as well as in humans when taking more than 10 drops in a day, or in a child taking 2–3 drops over several days. For this reason, the volatile oil should be used with extreme caution and is not recommended for those with epilepsy or any other seizure disorder.

A survey of the literature documented essential oils of hyssop and nine other plants — including eucalyptus, fennel, pennyroyal, rosemary, sage, savin, tansy, thuja, turpentine, and wormwood — to be powerful convulsants due to their content of highly reactive monoterpene ketones, such as camphor, pinocamphone, thujone, cineole, pulegone, sabinyl acetate, and fenchone.

8.2 Topical and Oral Essential Oil Use

The volatile oils include pinocamphone, which is mildly toxic. Hyssop oil is used as a fragrance and should not be taken orally.

8.3 Herb Preparations (Tea, Tincture) vs. Concentrated Oil

Tea and tincture of hyssop are unlikely to cause adverse effects in typical use. The risk profile differs substantially between dilute herbal infusions/tinctures and concentrated essential oils; the former deliver far lower concentrations of pinocamphone than the latter.

8.4 Reported Side Effects

Side effects reported at standard doses are mild and include gastrointestinal upset, anxiety, and tremors.

8.5 Hepatotoxicity

Hyssop is widely used and has not been implicated in causing liver injury. NIH LiverTox lists hyssop as having no documented hepatotoxic cases.

8.6 Pregnancy

The herb is not recommended during pregnancy. This recommendation reflects the plant's traditional classification as an emmenagogue (a substance used historically to stimulate or regulate menstrual flow).

8.7 Interactions with Anti-Seizure Medications

Given the convulsant properties of the essential oil, there is a pharmacodynamic concern for interaction with anti-epileptic medications. Increasing the dose of pinocamphone to 1.25 g/kg leads to rhythmic myoclonus, subsequently to one or several tonic, clonic, or tonic-clonic seizures, and eventually lethal convulsive status (in animal models). The linalool-dominant chemotypes (e.g., var. decumbens from France) carry substantially lower pinocamphone content and thus a different risk profile, but identification of chemotype in commercial preparations is generally not disclosed to consumers.

8.8 Methyl Eugenol

Carcinogenic properties might arise due to methyl eugenol, but hyssop essential oils rich in this constituent are quite rare. Regulatory bodies in the European Union have restricted methyl eugenol as a flavoring agent due to genotoxic and carcinogenic potential at high doses; this is only a relevant concern for chemotypes in which methyl eugenol is a significant fraction of the oil.

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