Table of Contents
- Current evidence position
- Key safety points
- Brad's videos on this topic
- Overview
- Forms and Bioavailability
- Evidence for Benefits
- Recommended Dosing
- Safety and Side Effects
- Drug Interactions
- Dietary Sources
- References
Current evidence position
Brad has not made a video on this topic; this is a summary of the evidence, not his view. A 2017 systematic review found 24 human studies of tulsi; all reported favourable outcomes and none reported significant adverse events, but the authors called for more work on dose, dose form and who is most likely to benefit [3]. The largest placebo-controlled trial gave adults with stress symptoms 1,200 mg a day of holy basil extract actives (OciBest) for six weeks, and control of their stress symptoms improved 39% more than with placebo [14]. Smaller trials suggest holy basil leaves may lower fasting blood sugar in type 2 diabetes and that leaf extracts may affect anxiety, attention and immune markers, but these trials were small or short, and the anxiety study had no placebo group [15, 17, 18, 24]. People who take diabetes medicines should talk to their doctor first [15, 30]; women who are trying to conceive, pregnant or breastfeeding should avoid it, because a rat study raised fertility concerns [38] and safety in pregnancy and breastfeeding has not been studied.
Key safety points
- Holy basil may lower blood sugar, and in rats a leaf extract strengthened the effect of insulin [15, 30]. If you take insulin or other diabetes medicines, talk to your doctor first and watch for low blood sugar.
- In animals, holy basil seed oil lengthened blood clotting time about as much as aspirin did [12]. If you take warfarin, another anticoagulant or an antiplatelet drug, ask your doctor before using it.
- In female rats given a high dose, a leaf extract raised progesterone; the authors concluded this may impair fertility, but no mating test was done [38, 39]. Avoid the supplements if you are trying to conceive, pregnant or breastfeeding; safety in pregnancy and breastfeeding is unstudied.
- In mice, a leaf extract lowered the thyroid hormone T4 [32]. If you have thyroid disease or take levothyroxine, ask your doctor first.
- Eugenol, a compound in both holy basil and clove oil, harmed liver cells in the lab, and a baby who swallowed clove oil developed liver failure [19, 34]. With liver disease, talk to your doctor first.
- Eugenol in dental products can cause skin reactions and, rarely, a serious allergic reaction [35, 36]. Avoid holy basil if you are allergic to eugenol or clove; for trouble breathing or swelling of the face or throat, call your local emergency number (111 in NZ, 000 in Australia, 911 in the US, 999 in the UK).
- Human studies reviewed in 2017 reported no significant adverse events; one trial reported brief mild nausea [3].
Brad's videos on this topic
None yet.
1. Overview
Holy basil (Ocimum sanctum, also sold as Ocimum tenuiflorum) is a plant native to the Indian subcontinent, where it is called tulsi [3, 14]. It is highly revered in the Ayurvedic and Siddha medical systems, and a 2014 review calls it preeminent among Ayurvedic herbs [1, 3].
An adaptogen is a substance said to help the body cope with stress. A 2014 review describes tulsi countering chemical, physical, metabolic and psychological stress [1].
The leaves contain several bioactive compounds, including eugenol and ursolic acid, and rosmarinic acid is among the other possible active compounds [3]. Studies have looked most at these:
- Eugenol has been described as the constituent largely responsible for tulsi's therapeutic effects [4].
- Ursolic acid is a plant triterpene that acts on targets involved in cell death, tumour spread, blood vessel growth and inflammation [20].
- Rosmarinic acid is a plant compound with antiviral, antibacterial, anti-inflammatory and antioxidant activity [8].
- Ocimumosides A and B are compounds isolated from the leaves that normalised stress-induced changes, including raised corticosterone, in rats [9].
Human trials have tested tulsi for metabolic disorders, cardiovascular disease, immunity and neurocognition [3]. The 2017 systematic review found that all 24 studies reported favourable outcomes, but it called for more work to clarify the dose and dose form [3].
Three Main Varieties
Trials have used plants named Ocimum sanctum [18, 24] and Ocimum tenuiflorum [14]; both names refer to holy basil.
Historical and Traditional Context
Traditional Indian medicine has used tulsi leaves, stems, seeds and roots for bronchitis, asthma, malaria, diarrhoea, skin diseases, arthritis, eye diseases, fever and insect bites [4].
A 2014 review argued that scientific research is now confirming tulsi's traditional benefits [1].
2. Forms and Bioavailability
Holy basil comes as dried leaf powder, leaf extract capsules, tea and seed (fixed) oil.
Available Forms
| Form | Description | Studied in people |
|---|---|---|
| Leaf powder or fresh leaves | Dried or fresh leaves | Blood sugar [15] |
| Leaf extract | Concentrated alcohol or water extract of the leaves | Stress, anxiety, cognition, immunity [14, 17, 18, 24] |
| Seed (fixed) oil | Oil pressed from the seeds | Animal studies only [12] |
| Tulsi tea | Dried leaves steeped in hot water | Not tested in the trials above |
Key Active Compounds and Standardization
OciBest, the extract tested in the largest stress trial, is a branded extract of Ocimum tenuiflorum [14].
Leaf Powder vs. Extract
- Leaf powder is the whole dried leaf. The blood sugar trial used holy basil leaves [15].
- Extracts concentrate the leaf compounds. The stress, anxiety, cognition and immunity trials used extracts at daily doses of 300 to 1,200 mg [14, 17, 18, 24].
Bioavailability Considerations
How well people absorb eugenol, ursolic acid and rosmarinic acid from holy basil supplements has not been well studied.
Storage
Store holy basil supplements as the label directs.
3. Evidence for Benefits
Stress and Anxiety
Holy basil has been studied most for stress, in line with its traditional use as an adaptogen [1].
Placebo-controlled trial for stress: Adults with stress symptoms took either OciBest, 1,200 mg a day of holy basil extract actives (71 people), or placebo (79 people) for six weeks [14]. Symptom scores for forgetfulness, sexual problems of recent origin, frequent exhaustion and recent sleep problems fell more with OciBest than with placebo, and so did the total symptom score [14]. Overall control of stress symptoms was 39% better than with placebo, and no adverse events were reported [14].
Uncontrolled trial for generalized anxiety disorder (n=35): Thirty-five adults with generalized anxiety disorder took 500 mg of a holy basil leaf extract twice daily after meals and were assessed up to day 60 [17]. Anxiety, stress and depression scores fell, and attention improved [17]. Every participant took holy basil, so the study cannot separate its effect from a placebo response or natural change.
Placebo-controlled trial for cognition and anxiety: Healthy adults took 300 mg capsules of an ethanol leaf extract or placebo each day over 30 days [18]. Reaction time and error rates on memory and attention tests improved more with the extract [18]. Salivary cortisol and anxiety scores improved over time in the extract group, but the difference from placebo was not significant [18].
Animal evidence for anti-stress mechanisms: In rats, compounds isolated from holy basil leaves normalised stress-induced rises in blood sugar and corticosterone and enlargement of the adrenal glands [9].
Summary of stress/anxiety evidence: One placebo-controlled trial supports 1,200 mg a day of extract actives for stress symptoms [14]. The anxiety disorder evidence is preliminary because the trial had no control group [17].
Blood Sugar and Diabetes
Holy basil has been studied for blood sugar control after rat studies found that leaf extracts lowered blood sugar [15, 30].
In laboratory studies, leaf extracts stimulated insulin release from rat pancreas tissue and beta cells [22].
Placebo-controlled trial in type 2 diabetes: In a single-blind crossover trial in patients with type 2 diabetes, fasting blood glucose was 17.6% lower and blood glucose after meals 7.3% lower during treatment with holy basil leaves than during treatment with placebo leaves [15]. Urine glucose followed the same trend and total cholesterol fell slightly [15].
Animal evidence: In rats, an alcoholic leaf extract lowered blood sugar in normal and diabetic animals and strengthened the effect of injected insulin [30].
Effect on metabolic parameters (systematic review): The 2017 systematic review included studies of metabolic disorders and concluded that tulsi may help in diabetes and metabolic syndrome, while calling for more work on dose and dose form [3].
Summary of blood sugar evidence: One small crossover trial found lower fasting and after-meal blood sugar with holy basil leaves [15]. Anyone taking insulin or other diabetes medicines should talk to their doctor first, because the effects may add up (see Safety).
Immune Function
Traditional practice holds that eating tulsi leaves on an empty stomach boosts immunity [24].
Placebo-controlled trial in healthy adults (n=22): In a double-blind crossover trial, 24 healthy volunteers took capsules of an ethanol leaf extract or placebo on an empty stomach, and 22 finished [24]. After 4 weeks, interferon-gamma, interleukin-4 and the percentages of T-helper cells and natural killer cells rose with the extract compared with placebo [24].
The trial measured immune markers, not infections [24].
Animal evidence for immune modulation: In rats, leaf extracts raised antibody levels and boosted cell-based immune responses [26].
Radioprotective effects: Claims that holy basil protects against radiation rest on animal studies; clinical trials in people appear to be lacking.
Anti-Inflammatory and Analgesic Effects
Holy basil is promoted for pain and inflammation, partly because of its eugenol content [4].
Mechanism: In mice and rats, holy basil seed oil reduced blood vessel leakage and white cell movement after an inflammatory trigger [29].
Animal studies: In mice, an alcoholic leaf extract reduced pain responses, acting through both the brain and the body [5].
Human evidence: The human studies in the 2017 systematic review covered metabolic disorders, cardiovascular disease, immunity and brain function, not pain [3].
Wound healing: A 2014 review lists wound healing among tulsi's possible uses, based on its antimicrobial activity [1].
Antioxidant Activity
Animal antioxidant data: In mice, a leaf extract raised the antioxidant enzymes superoxide dismutase and catalase and lowered lipid peroxidation in the liver [32].
Relevance to chronic disease: Antioxidant activity in animals is not a reason on its own to take holy basil.
Cognitive Function
Placebo-controlled trial: As described above, 300 mg capsules of an ethanol leaf extract taken each day over 30 days improved reaction time and error rates on memory and attention tests compared with placebo [18].
Animal evidence: In rats, a leaf extract protected the brain against oxidative damage after blocked blood flow and prevented memory deficits from long-term low blood flow [28].
Clinical significance: Whether these effects extend to older adults or people with cognitive decline is unknown.
Cardiovascular and Lipid Effects
Blood pressure: In anaesthetised dogs, holy basil seed oil lowered blood pressure, apparently by widening blood vessels [12].
Lipid profile: In the diabetes trial, total cholesterol fell slightly with holy basil leaves [15]. In rabbits, fresh leaves added to the diet lowered total cholesterol, triglycerides and LDL cholesterol and raised HDL cholesterol [13].
Anti-platelet activity: In animals, holy basil seed oil lengthened blood clotting time about as much as aspirin, possibly by blocking platelet clumping [12]. This raises a theoretical concern about combining holy basil with blood thinners.
Respiratory Health
Traditional medicine has used tulsi for bronchitis and asthma [4].
Mechanism: Tulsi shows broad antimicrobial activity in laboratory studies [1].
Human evidence: Controlled trials of holy basil for respiratory conditions are lacking.
Hepatoprotective (Liver-Protective) Effects
Animal evidence: A 2014 review reports that tulsi protected organs and tissues against industrial pollutants and heavy metals in animal studies [1].
These findings come from animals and have not been confirmed in people.
Anticancer Properties (Preclinical Only)
Preclinical findings:
- Ursolic acid acts on targets involved in cell death, tumour spread and blood vessel growth in laboratory studies [20]
Human evidence: Holy basil appears not to have been tested in cancer trials, and the human studies in the 2017 systematic review did not include cancer [3].
4. Recommended Dosing
The doses below are those the trials used; the 2017 systematic review called for more work to clarify dosing [3].
By Indication
For stress: 1,200 mg a day of OciBest extract actives for six weeks, in the one placebo-controlled stress trial [14].
For generalized anxiety: A leaf extract, 500 mg twice daily after meals, in a trial without a placebo group [17].
For blood sugar reduction in type 2 diabetes: The placebo-controlled crossover trial used holy basil leaves [15]. Anyone taking insulin or other diabetes medicines should talk to their doctor first so that blood sugar and medicine doses can be monitored.
For immune support: 300 mg capsules of an ethanol leaf extract taken without food for 4 weeks, in a small placebo-controlled trial [24].
For cognitive function: 300 mg capsules of an ethanol leaf extract each day over 30 days [18].
General Supplementation
Outside these uses, the trials used extracts at daily doses of 300 to 1,200 mg [14, 17, 18, 24].
How to Take
The immunity trial gave the extract without food, and the anxiety trial gave it after meals [17, 24].
Duration of Use
The trials described here lasted from 4 weeks [24] up to day 60 [17]. Longer-term safety is unknown.
Triterpene Content as a Quality Benchmark
No triterpene content has been linked to a clinical effect; the 2017 systematic review called for studies to clarify the dose and dose form [3].
5. Safety and Side Effects
The 2017 systematic review found no significant adverse events in 24 human studies [3]. The trials were small, and long-term safety is unknown.
Reported Side Effects
- Adverse events: None were reported in the six-week stress trial [14].
- Nausea: In the 2017 systematic review, one trial (Satapathy 2016) reported brief mild nausea [3].
Pregnancy and Breastfeeding
In female rats given a high dose, a leaf extract raised progesterone; the authors concluded this may impair fertility, but no mating test was done [38, 39].
Recommendation: Women who are trying to conceive should avoid holy basil supplements. Safety in pregnancy and breastfeeding has not been studied, so it is best avoided then too.
Thyroid Function
In male mice, a leaf extract significantly decreased serum T4, with no marked change in serum T3 [32].
Clinical significance: This finding comes from mice; human data appear to be lacking. People with hypothyroidism or those taking levothyroxine should discuss holy basil with their doctor.
Blood Pressure Effects
In anaesthetised dogs, holy basil seed oil lowered blood pressure [12]. Its relevance to leaf supplements in people is uncertain.
Liver Safety
In cultured rat liver cells, eugenol depleted the protective antioxidant glutathione and caused cell damage, mainly through a breakdown product [19].
Clove oil, which also contains eugenol, can cause severe poisoning. One case of clove oil ingestion caused coma, seizures, a blood clotting disorder and acute liver damage [33]. A 3-month-old who swallowed less than 8 mL of clove oil developed liver failure and recovered after hospital treatment with N-acetylcysteine [34]. If a child swallows clove oil, call your local emergency number (111 in NZ, 000 in Australia, 911 in the US, 999 in the UK) or go to the emergency department.
Risk assessment: People with liver disease should talk to their doctor before using holy basil.
Allergic Reactions
Eugenol used in dentistry can cause contact dermatitis and hives [35, 36]. Serious allergic reactions to eugenol are rare but have been reported [35]. If you are allergic to eugenol or clove, avoid holy basil. If you have trouble breathing or swelling of the face or throat, call your local emergency number (111 in NZ, 000 in Australia, 911 in the US, 999 in the UK).
Blood Sugar — Risk of Hypoglycemia
Holy basil lowered blood sugar in a small trial, and in rats a leaf extract strengthened the effect of insulin [15, 30]. People taking insulin, sulfonylureas or other glucose-lowering medicines should watch for low blood sugar; their doses may need adjusting.
If someone with diabetes is unconscious, having a seizure, or cannot swallow safely, call your local emergency number (111 in NZ, 000 in Australia, 911 in the US, 999 in the UK). Do not give food or drink by mouth.
Fertility
In male rats, a leaf extract reduced sperm count and movement; the effect reversed 2 weeks after treatment stopped [37]. Men trying to conceive may wish to avoid high-dose holy basil until human data exist.
Surgical Precaution
Because of the clotting and blood sugar findings above, tell your surgeon before any planned operation if you take holy basil.
6. Drug Interactions
Drug interactions with holy basil have not been studied in people. The cautions below come from animal studies and from how its compounds act.
Blood Sugar-Lowering Medications
| Drug Class | Examples | Concern | Recommendation |
|---|---|---|---|
| Insulin | All formulations | Additive low blood sugar [30] | Monitor blood sugar closely |
| Sulfonylureas | Glipizide, gliclazide | Possible additive low blood sugar (theoretical); in lab tests, tolbutamide strengthened the extract's insulin release [22] | Monitor blood sugar |
| Other glucose-lowering medicines | Metformin, SGLT2 inhibitors, GLP-1 receptor agonists | Possible additive blood sugar lowering (theoretical) [15] | Monitor blood sugar |
Anticoagulant and Antiplatelet Medications
Holy basil seed oil lengthened clotting time in animals [12]. This has not been tested for leaf supplements in people, but a theoretical interaction exists:
| Drug | Concern | Recommendation |
|---|---|---|
| Warfarin, direct oral anticoagulants (apixaban, rivaroxaban) | Possible added blood-thinning effect | Ask your doctor first |
| Aspirin, clopidogrel | Possible added antiplatelet effect | Ask your doctor first |
Thyroid Medications
Based on the mouse data showing lower T4 [32]:
| Drug | Concern | Recommendation |
|---|---|---|
| Levothyroxine | Holy basil may lower thyroid hormone levels | Monitor thyroid function; discuss with your doctor |
Sedatives and CNS Depressants
In rats, holy basil seed oil lengthened sleep induced by the sedative pentobarbitone [12]. Taking holy basil with sedatives or sleeping tablets may add to drowsiness.
CYP450 Enzyme Interactions
The longer pentobarbitone sleep in rats suggests the seed oil may slow the liver enzymes that clear that drug [12]. Whether holy basil supplements change the levels of other medicines in people is unknown.
General Recommendation
If you take prescription medicines, check with your doctor or pharmacist before starting. This matters most for diabetes medicines, blood thinners, thyroid medicines and sedatives.
7. Dietary Sources
Holy basil is not a usual part of Western diets. In India, tulsi is grown for spiritual and practical reasons and used in daily rituals [1].
Culinary Use
- Tulsi tea: Dried holy basil leaves steeped in hot water. The amount of active compounds in a cup varies and has not been standardized.
Estimated Phytochemical Intake from Dietary Sources
No standard values exist for how much eugenol or triterpenes holy basil food or tea provides.
Growing Holy Basil
A 2014 review argues that growing tulsi, especially organically, has practical as well as spiritual value [1].
Limitations of Dietary Sources
Tea and fresh leaves give lower and more variable amounts of active compounds than the extracts used in the trials.
8. References
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[28] Yanpallewar SU, Rai S, Kumar M, Acharya SB. "Evaluation of antioxidant and neuroprotective effect of Ocimum sanctum on transient cerebral ischemia and long-term cerebral hypoperfusion." Pharmacol Biochem Behav. 2004;79(1):155-164. PMID: 15388295. doi: 10.1016/j.pbb.2004.07.008
[29] Singh S, Majumdar DK. "Effect of Ocimum sanctum fixed oil on vascular permeability and leucocytes migration." Indian J Exp Biol. 1999;37(11):1136-1138. PMID: 10783746
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[32] Panda S, Kar A. "Ocimum sanctum leaf extract in the regulation of thyroid function in the male mouse." Pharmacol Res. 1998;38(2):107-110. PMID: 9721597. doi: 10.1006/phrs.1998.0338
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[34] Eisen JS, Koren G, Juurlink DN, Ng VL. "N-acetylcysteine for the treatment of clove oil-induced fulminant hepatic failure." J Toxicol Clin Toxicol. 2004;42(1):89-92. PMID: 15083943. doi: 10.1081/CLT-120028751
[35] Barkin ME, Boyd JP, Cohen S. "Acute allergic reaction to eugenol." Oral Surg Oral Med Oral Pathol. 1984;57(4):441-442. PMID: 6584843. doi: 10.1016/0030-4220(84)90166-X
[36] Tammannavar P, Pushpalatha C, Jain S, Sowmya SV. "An unexpected positive hypersensitive reaction to eugenol." BMJ Case Rep. 2013;2013:bcr2013009464. PMID: 24049087. doi: 10.1136/bcr-2013-009464
[37] Ahmed M, Ahamed RN, Aladakatti RH, Ghosesawar MG. "Reversible anti-fertility effect of benzene extract of Ocimum sanctum leaves on sperm parameters and fructose content in rats." J Basic Clin Physiol Pharmacol. 2002;13(1):51-59. PMID: 12099405. doi: 10.1515/JBCPP.2002.13.1.51
[38] Poli V, Challa C. "A comparative study of eugenol and Ocimum sanctum Linn. leaf extract on the antifertility effect in female albino rats." J Chin Med Assoc. 2019;82(3):231-234. PMID: 30908416. doi: 10.1097/JCMA.0000000000000034
[39] Li YT, Yeh CC, Wang PH. "Without mating test, it is hard to say that the reproductive performance of rats is decreased." J Chin Med Assoc. 2019;82(11):884. PMID: 31305348. doi: 10.1097/JCMA.0000000000000143
