Holy Basil

Tulsi is tulasi, and its standing in India is religious before it is medical. It is grown in courtyards and temple grounds, tended daily, and worshipped in Hinduism, where every part of the plant is held sacred ^{1Reference 1Cohen · 2014ReviewTulsi — Ocimum sanctum: A herb for all reasons — reviewView study →}. The drug is the leaf, fresh or dried.

Ayurveda classifies it as a rasayana, a rejuvenative taken over long periods rather than for an acute complaint. It is pungent and bitter in taste with a heating potency, and pacifies kapha and vata.

It is given to build resilience to stress and calm the mind, to ease cough, cold and respiratory congestion, and to aid digestion. The fresh leaf is chewed, or a simple leaf infusion is drunk daily.

In traditional Indian medicine the leaves, stem, flowers, root and seeds have been used for bronchitis, asthma, malaria, diarrhoea and dysentery, skin diseases, arthritis, painful eye diseases, chronic fever and insect bites ^{21Reference 21Prakash et al. · 2005ReviewTherapeutic uses of Ocimum sanctum Linn (tulsi) with a note on eugenol and its pharmacological actions: a short review — reviewView study →}.

Tulsi is also part of daily religious life. Morning and evening observances can involve eating its leaves or drinking the tea, it is used to make holy water, and its wood and seeds are strung into malas, the bead strings used in meditation and chanting ^{1Reference 1Cohen · 2014ReviewTulsi — Ocimum sanctum: A herb for all reasons — reviewView study →}.

In a six-week double-blind trial, 150 adults with general stress took the standardised extract OciBest (1,200 mg of actives a day, as 400 mg three times daily) or placebo. Forgetfulness, exhaustion, sleep problems and recent sexual problems fell significantly more on the extract, and overall improvement was 39% greater than on placebo. No side effects were reported ^{2,3Reference 2Jamshidi et al. · 2017Systematic reviewThe clinical efficacy and safety of tulsi in humans: a systematic review of the literature — systematic reviewView study →Reference 3Saxena et al. · 2012RCTEfficacy of an extract of Ocimum tenuiflorum (OciBest) in the management of general stress — randomised placebo-controlled trialView study →}.

A 2022 eight-week trial gave 100 stressed adults 125 mg of a standardised extract (Holixer) twice daily or placebo. Perceived stress and insomnia scores improved more on the extract, and hair cortisol was lower at eight weeks. In a laboratory stress test, the extract group had lower salivary cortisol, salivary amylase and blood pressure responses ^{5Reference 5Lopresti et al. · 2022RCTA randomised, double-blind, placebo-controlled trial investigating the effects of a standardised Ocimum tenuiflorum extract — randomised controlled trialView study →}.

In an earlier 60-day trial, 35 adults with generalised anxiety disorder took 500 mg of ethanolic leaf extract twice daily. Anxiety, stress and depression scores fell significantly. The trial had no control group ^{2,4Reference 2Jamshidi et al. · 2017Systematic reviewThe clinical efficacy and safety of tulsi in humans: a systematic review of the literature — systematic reviewView study →Reference 4Bhattacharyya et al. · 2008Clinical trialControlled programmed trial of Ocimum sanctum leaf on generalized anxiety disorders — controlled clinical trialView study →}.

In a randomised trial of 44 thyroid-cancer patients having radioiodine therapy, those who drank tea made from 2 g of holy basil leaf after each meal for four days had a smaller rise in anxiety scores than those who drank water ^{28Reference 28Nomura K et al. · 2023RCTBenefits of basil tea for patients with differentiated thyroid cancer during radioiodine therapy: A randomized controlled trialView study →}.

Gap: the trials are small and short, used different extracts and doses, and only one measured cortisol.

In a single-blind, placebo-controlled crossover trial, 40 adults with type 2 diabetes took 2.5 g/day of dried holy basil leaf powder or spinach-leaf placebo for five-week periods. Fasting blood glucose fell by 21.0 mg/dL (17.6%) and after-meal glucose by 15.8 mg/dL (7.3%) compared with placebo, and total cholesterol fell slightly ^{2,6Reference 2Jamshidi et al. · 2017Systematic reviewThe clinical efficacy and safety of tulsi in humans: a systematic review of the literature — systematic reviewView study →Reference 6Agrawal et al. · 1996RCTRandomised placebo-controlled, single-blind trial of holy basil leaves in patients with non-insulin-dependent diabetes mellitus — randomised controlled trialView study →}.

In an open-label pilot trial, 16 overweight or obese young adults took 250 mg of leaf extract twice daily for eight weeks, and 14 had no treatment. Triglycerides, LDL, VLDL, BMI, plasma insulin and insulin resistance fell in the tulsi group, and the rise in HDL was significant against the untreated group. Liver enzymes did not change ^{29Reference 29Satapathy S et al. · 2017RCTEffect of Tulsi (Ocimum sanctum Linn.) Supplementation on Metabolic Parameters and Liver Enzymes in Young Overweight and Obese Subjects — open-label randomised clinical trialView study →}.

The 2017 review found 17 clinical studies on metabolic conditions, including ten in type 2 diabetes or metabolic syndrome that measured blood glucose ^{2Reference 2Jamshidi et al. · 2017Systematic reviewThe clinical efficacy and safety of tulsi in humans: a systematic review of the literature — systematic reviewView study →}.

Gap: the controlled glucose trial is small, single-blind and from 1996, and the lipid trial was open-label. No modern, well-powered trial has confirmed the glucose or lipid effect, and the effect sizes are modest.

In a triple-blind trial of 108 students, an Ocimum sanctum mouthwash reduced dental plaque and gum inflammation as effectively as chlorhexidine over 15 and 30 days, with no side effects reported ^{12Reference 12Gupta et al. · 2014RCTA randomised controlled clinical trial of Ocimum sanctum and chlorhexidine mouthwash on dental plaque and gingival inflammation — randomised controlled trialView study →}.

A 4% tulsi toothpaste reduced plaque and gingivitis in 84 children aged 14 to 15 over 21 days, as effectively as a fluoride toothpaste and more than placebo ^{13Reference 13Nadar et al. · 2020RCTComparative evaluation of efficacy of 4% tulsi extract (Ocimum sanctum), fluoridated and placebo dentifrices against gingivitis and plaque among 14–15 years school children — triple-blinded randomised controlled trialView study →}.

After scaling, 60 patients rinsed with tulsi, aloe vera or chlorhexidine mouthwash twice daily. All three were equally effective at 30 days, though the herbal rinses lagged behind chlorhexidine at 15 days ^{14Reference 14Penmetsa et al. · 2019RCTEfficacy of Ocimum sanctum, Aloe vera and chlorhexidine mouthwash on gingivitis — randomised controlled comparative trialView study →}.

In 60 people with oral submucous fibrosis, a scarring condition of the mouth lining, three months of topical tulsi paste reduced burning and improved mouth opening. The study had no control group ^{31Reference 31Biswas D et al. · 2022Clinical trialEfficacy of topical tulsi (Ocimum sanctum) paste for the management of oral submucous fibrosis - A clinical studyView study →}.

In the radioiodine trial, holy basil tea lessened the rise in cariogenic bacteria, ammonia, protein and blood in the saliva ^{28Reference 28Nomura K et al. · 2023RCTBenefits of basil tea for patients with differentiated thyroid cancer during radioiodine therapy: A randomized controlled trialView study →}.

This is local use in the mouth, not an effect of drinking tulsi tea.

Gap: follow-up is short, the samples are small and the formulations differ between trials.

In a double-blind, placebo-controlled crossover trial, 24 healthy volunteers took 300 mg capsules of ethanolic tulsi leaf extract, and 22 completed. After four weeks, interferon-γ, interleukin-4, T-helper cells and natural-killer cells had all risen significantly compared with placebo ^{8Reference 8Mondal et al. · 2011RCTDouble-blinded randomised controlled trial for immunomodulatory effects of tulsi (Ocimum sanctum) leaf extract on healthy volunteers — randomised controlled trialView study →}.

The endpoints are immune-cell markers in healthy people, not clinical outcomes such as infection rates.

Gap: a small sample and surrogate markers only. No trial has shown that tulsi reduces actual infections or illness.

In human monocytic (THP-1) cells, alcoholic and water extracts of the dried leaf, and pure eugenol, reduced the release of TNF-α, lowered the expression of inflammatory cytokines and chemokines, and blocked NF-κB from entering the cell nucleus ^{10Reference 10Choudhury et al. · 2014In vitroOcimum sanctum leaf extracts attenuate human monocytic (THP-1) cell activation — in vitroView study →}.

In animal models of acute and chronic inflammation, tulsi’s anti-inflammatory activity has been attributed to eugenol and linoleic acid and to inhibition of both the cyclooxygenase and lipoxygenase pathways ^{1Reference 1Cohen · 2014ReviewTulsi — Ocimum sanctum: A herb for all reasons — reviewView study →}.

Gap: no trial has tested tulsi against an inflammatory disease in humans.

Holy basil essential oil was one of four oils, among 10 essential oils and 10 absolutes from Thai aromatic plants, with high activity in DPPH and lipid-peroxidation (TBARS) tests ^{19Reference 19Leelapornpisid et al. · 2015In vitroPotential of native Thai aromatic plant extracts (including holy basil oil) in antiwrinkle body creams: antioxidant assays — in vitroView study →}.

Results vary with chemotype. A methyl-eugenol-rich holy basil oil from southern India showed very weak antioxidant activity, and methyl eugenol on its own showed none ^{25Reference 25Joshi · 2013In vitroChemical composition, in vitro antimicrobial and antioxidant activities of the essential oils of Ocimum gratissimum, O. sanctum and their major constituents — in vitroView study →}. Purple Krishna tulsi has a higher phenolic content and antioxidant capacity than the wild Vana form ^{1Reference 1Cohen · 2014ReviewTulsi — Ocimum sanctum: A herb for all reasons — reviewView study →}.

Gap: this is laboratory work, much of it on the essential oil rather than the leaf or tea. No study has measured an antioxidant effect in people.

In rats with fatty liver disease from a high-fat diet, a water extract of holy basil flowers lowered LDL cholesterol, liver cholesterol and liver triglycerides, reduced signs of liver injury and raised HDL. Unlike fenofibrate, its benefit did not work through choline metabolism ^{15Reference 15Taesuwan et al. · 2024AnimalHoly basil (Ocimum sanctum L.) flower and fenofibrate improve lipid profiles in rats with metabolic dysfunction-associated steatotic liver disease (MASLD): the role of choline metabolism — animal in vivo studyView study →}.

A second 12-week rat study of the flower extract found that it raised cholesterol excretion, reduced fat build-up in the liver, activated AMPK and lowered inflammatory gene expression ^{32Reference 32Inchai J et al. · 2026AnimalLipid-lowering and hepatoprotective effects of Ocimum sanctum L. (Thai holy basil) flower against MASLD and liver inflammation in ratsView study →}.

An ethanolic leaf extract protected rat liver against carbon-tetrachloride injury, lowering liver enzymes and restoring antioxidant enzymes ^{33Reference 33Maaz M et al. · 2026In vitroProtective Effects of the Ethanolic Leaf Extract of Ocimum sanctum L. on Collagen-Induced Human Platelet Aggregation and CCl(4)-Induced Hepatotoxicity in Rats: Molecular Docking Analysis of Platelet Activation Signaling Targets — in vitro and animal in vivo studyView study →}.

Gap: the evidence is animal-only. The one human trial that measured liver enzymes found no change ^{29Reference 29Satapathy S et al. · 2017RCTEffect of Tulsi (Ocimum sanctum Linn.) Supplementation on Metabolic Parameters and Liver Enzymes in Young Overweight and Obese Subjects — open-label randomised clinical trialView study →}.

In a placebo-controlled study, healthy adults took 300 mg/day of ethanolic leaf extract for 30 days. Reaction time and error rate on the Sternberg and Stroop tests improved significantly more than on placebo, and so did P300 latency, a brainwave measure of processing speed. Salivary cortisol and anxiety scores improved only within the extract group ^{9Reference 9Sampath et al. · 2015RCTHoly basil (Ocimum sanctum) leaf extract enhances specific cognitive parameters in healthy adult volunteers: a placebo-controlled study — randomised controlled trialView study →}.

Gap: a single small, short trial of computerised test scores in healthy volunteers, with no data in people with cognitive impairment.

In rodents, tulsi and several of its compounds, including eugenol, rosmarinic acid, apigenin, myrtenal, luteolin, β-sitosterol and carnosic acid, prevented chemically induced skin, liver, oral and lung cancers ^{11Reference 11Baliga et al. · 2013ReviewOcimum sanctum L (holy basil or tulsi) and its phytochemicals in the prevention and treatment of cancer — reviewView study →}.

The isolated flavone vicenin (vicenin-2) inhibited Wnt/β-catenin signalling, halted the cell cycle and triggered cell death in HT-29 colon cancer cells ^{18Reference 18Yang et al. · 2018In vitroVicenin-2 inhibits Wnt/β-catenin signalling and induces apoptosis in HT-29 human colon cancer cell line — in vitroView study →}.

Gap: cell-line and rodent chemoprevention only, much of it on isolated compounds. There is no clinical cancer evidence.

In mice, a water extract of tulsi and its flavonoids orientin and vicenin protected against radiation sickness and death, and selectively protected normal tissue during tumour irradiation. Eugenol, rosmarinic acid, apigenin and carnosic acid prevented radiation-induced DNA damage ^{11Reference 11Baliga et al. · 2013ReviewOcimum sanctum L (holy basil or tulsi) and its phytochemicals in the prevention and treatment of cancer — reviewView study →}.

In lung-cancer cells, vicenin-2 made the cancer cells more sensitive to radiation by lowering Akt activity ^{17Reference 17Baruah et al. · 2019In vitroVicenin-2 acts as a radiosensitiser of non-small-cell lung cancer by lowering Akt expression — in vitroView study →}.

In 44 thyroid-cancer patients, drinking holy basil leaf tea for four days during radioiodine therapy protected salivary-gland function on scintigraphy compared with water ^{28Reference 28Nomura K et al. · 2023RCTBenefits of basil tea for patients with differentiated thyroid cancer during radioiodine therapy: A randomized controlled trialView study →}.

Gap: the human evidence is one small, short trial on the salivary glands. The rest is animal and cell-line data.

Side effects. Holy basil is well tolerated as a food, tea and standardised extract. Human studies lasting 2 to 13 weeks reported no significant side effects ^{2Reference 2Jamshidi et al. · 2017Systematic reviewThe clinical efficacy and safety of tulsi in humans: a systematic review of the literature — systematic reviewView study →}.

Diabetes medicines. It can modestly lower fasting and after-meal blood glucose and improved insulin resistance in one open-label trial, so people taking insulin or other diabetes medicines should watch for low blood sugar ^{6,29Reference 6Agrawal et al. · 1996RCTRandomised placebo-controlled, single-blind trial of holy basil leaves in patients with non-insulin-dependent diabetes mellitus — randomised controlled trialView study →Reference 29Satapathy S et al. · 2017RCTEffect of Tulsi (Ocimum sanctum Linn.) Supplementation on Metabolic Parameters and Liver Enzymes in Young Overweight and Obese Subjects — open-label randomised clinical trialView study →}.

Anticoagulant and antiplatelet drugs. An ethanolic leaf extract dose-dependently inhibited collagen-induced aggregation of human platelets in the laboratory, along with P-selectin expression and calcium mobilisation ^{33Reference 33Maaz M et al. · 2026In vitroProtective Effects of the Ethanolic Leaf Extract of Ocimum sanctum L. on Collagen-Induced Human Platelet Aggregation and CCl(4)-Induced Hepatotoxicity in Rats: Molecular Docking Analysis of Platelet Activation Signaling Targets — in vitro and animal in vivo studyView study →}. No human bleeding events are documented, but care is reasonable around surgery and alongside blood thinners.

Drug metabolism. No pharmacokinetic interaction study has been done in people. In human liver microsomes, eugenol, the main compound of the eugenol-type leaf oil, inhibited CYP1A2, CYP2C9, CYP2D6 and CYP3A4 ^{30Reference 30Alharbi NFM et al. · 2024In vitroEffect of eugenol on cytochrome P450 1A2, 2C9, 2D6, and 3A4 activity in human liver microsomes — in vitroView study →}. In goats, raw leaf juice for seven days raised the bioavailability of intravenous ceftriaxone ^{34Reference 34Dash JR et al. · 2024AnimalRaw Ocimum sanctum L. leaf extract modulates the pharmacokinetic of ceftriaxone and increases its bioavailability in staphylococcal mastitis — goat in vivo studyView study →}. Neither finding has been tested with the whole herb in people.

Fertility and pregnancy. A benzene extract of the leaves (250 mg/kg for 48 days) lowered sperm count and motility in male rats, and all measures returned to normal two weeks after stopping ^{16Reference 16Ahmed et al. · 2002AnimalReversible antifertility effect of benzene extract of Ocimum sanctum leaves on sperm parameters and fructose content in rats — animal in vivo studyView study →}. A leaf extract raised progesterone and impaired fertility in female rats ^{23Reference 23Poli et al. · 2019AnimalA comparative study of eugenol and Ocimum sanctum Linn. leaf extract on the antifertility effect in female albino rats — animal in vivo studyView study →}, and an aqueous leaf extract showed anti-implantation activity in pregnant rats ^{22Reference 22Vohora et al. · 1969AnimalAntifertility screening of plantsView study →}. Antifertility activity is listed among tulsi’s reported actions ^{21Reference 21Prakash et al. · 2005ReviewTherapeutic uses of Ocimum sanctum Linn (tulsi) with a note on eugenol and its pharmacological actions: a short review — reviewView study →}.

Quality. Holy basil leaf oil occurs in distinct chemotypes, and some Indian samples are 72–92% methyl eugenol ^{24,25Reference 24Rao et al. · 2011Chemical and biological diversity in fourteen selections of four Ocimum species — chemotype analysisView study →Reference 25Joshi · 2013In vitroChemical composition, in vitro antimicrobial and antioxidant activities of the essential oils of Ocimum gratissimum, O. sanctum and their major constituents — in vitroView study →}. Methyl eugenol is hepatotoxic after activation by CYP3A4, and IARC classes it as probably carcinogenic to humans (Group 2A) ^{35Reference 35Yang H et al. · 2026In vitroMechanistic Insight into Difference in Hepatotoxicity of Methyleugenol and Safrole — in vitroView study →}. The concentrated essential oil should not be taken internally.