Benefits
Stress and anxiety symptom relief
In three randomized trials, holy basil reduced self-rated stress or anxiety more than placebo or a water control: a 6-week whole-plant extract trial in 150 stressed adults (capsules supplied by the maker), an 8-week maker-funded extract trial in 100 stressed adults that also found lower hair cortisol, and a 4-day tea trial during radioiodine treatment. In the 8-week trial, mood scores did not differ from placebo.
Cognitive function
In a 30-day placebo-controlled trial in 40 healthy young men, 300 mg/day of leaf extract improved reaction time and error rate on the Sternberg task, reaction time on two Stroop tasks and error rate on one, and shortened P300 latency versus placebo; the Stroop facilitation task did not differ. This is one small trial that has not been replicated.
Fasting and post-meal blood glucose support
In a single-blind crossover trial in 40 adults with type 2 diabetes, 2.5 g/day of dried leaf taken for about 4 weeks lowered fasting glucose by about 21 mg/dL (17.6%) and post-meal glucose by about 16 mg/dL (7.3%) versus a spinach-leaf placebo. This is one small, older trial.
Antioxidant and COX enzyme activity (laboratory studies)
In laboratory assays, eugenol, rosmarinic acid and several flavonoids purified from holy basil leaves and stems showed antioxidant activity or inhibited the COX-1 and COX-2 enzymes at high test-tube concentrations. No controlled human trial has measured an anti-inflammatory benefit.
Mechanism of action
HPA axis modulation
In rats exposed to acute stress, ocimumoside A isolated from holy basil leaves normalized raised plasma corticosterone, blood glucose and adrenal enlargement, and ocimumoside B normalized most of these measures. In people, one maker-funded trial found lower hair cortisol at week 8 versus placebo, and during a laboratory stress test salivary cortisol was lower overall, but its change over the test did not differ between groups; the mechanism in humans has not been established.
COX enzyme inhibition
In test-tube assays, eugenol, rosmarinic acid and the flavonoids cirsilineol, cirsimaritin, isothymonin and apigenin inhibited cyclooxygenase 1 (COX-1) at 1000 micromolar, and all but isothymonin also inhibited COX-2. Human relevance at supplement doses is unknown.
Alpha-glucosidase and alpha-amylase inhibition
In laboratory assays, a methanol extract of holy basil leaves and its fractions inhibited alpha-glucosidase and alpha-amylase, enzymes that break down dietary starch, and the extract lowered blood glucose in diabetic rats. Whether this happens at supplement doses in people has not been tested.
Clinical trials
Randomized, double-blind, placebo-controlled trial of 300 mg/day ethanolic Ocimum sanctum leaf extract (supplied by the Central Council for Research in Ayurveda and Siddha) versus a sucrose placebo for 30 days, at AIIMS New Delhi; funded by an AIIMS institute research grant (CTRI/2010/091/006113). 44 healthy men aged 18 to 30 enrolled and 40 were analyzed; one stopped because of nausea. Salivary cortisol and State-Trait Anxiety scores fell within the extract group but did not differ from placebo. (Sampath et al. 2015, Indian J Physiol Pharmacol)
40 healthy young men analyzed (20 per group); 30-day intervention.
At day 30, versus placebo, the extract group had faster reaction time and fewer errors on the Sternberg task, faster reaction time on the Stroop neutral task, faster reaction time and fewer errors on the Stroop interference task, and shorter P300 latency. The Stroop facilitation task and P300 amplitude did not differ. Both groups improved over time, but the placebo group leveled off after day 15.
Randomized, single-blind, placebo-controlled crossover trial of 2.5 g/day dried holy basil leaf versus a spinach-leaf placebo, taken before breakfast, in 40 adults aged 41 to 65 with mild to moderate non-insulin-dependent diabetes (dose and placebo per the 2017 systematic review table). (Agrawal et al. 1996, Int J Clin Pharmacol Ther)
40 adults with mild to moderate type 2 diabetes.
Fasting blood glucose fell 21.0 mg/dL more during the holy basil period than the placebo period (p < 0.001; 17.6%), and post-meal glucose fell 15.8 mg/dL more (p < 0.02; 7.3%). Urine glucose followed the same trend, and total cholesterol fell mildly. Small, older, single-blind trial.
Randomized, double-blind, placebo-controlled trial of OciBest, a whole-plant Ocimum tenuiflorum extract developed by Natural Remedies (400 mg actives per capsule, 1,200 mg/day), for 6 weeks at two centers in Lucknow, India; 158 adults randomized. Natural Remedies supplied the coded capsules, and three authors, including the corresponding author, were from its research and development center; no separate funding statement is given. (Saxena et al. 2012, Evid Based Complement Alternat Med)
150 adults aged 18 to 65 with general stress symptoms analyzed (71 extract, 79 placebo).
At week 6, total stress symptom scores and scores for forgetfulness, recent sexual problems, frequent exhaustion and recent sleep problems fell more with the extract than placebo (p of 0.05 or less); no symptom differed at weeks 2 and 4. Overall improvement was 39% greater than placebo. No adverse effects were reported in either group.
Randomized, double-blind, placebo-controlled 8-week trial of Holixer, a standardized hydroalcoholic extract of the leaf-rich aerial parts of Ocimum tenuiflorum supplied by Natural Remedies, 125 mg twice daily (250 mg/day), in 100 adults aged 18 to 65 with ongoing stress and sleep complaints. Funded by Natural Remedies Pty Ltd, which also supplied the capsules; the lead author was managing director of a contract research organization funded by nutraceutical companies. Hair cortisol was measured once, at week 8, in 68 participants. ACTRN12621000609853. (Lopresti et al. 2022, Front Nutr)
100 adults aged 18 to 65 experiencing stress.
Perceived Stress Scale scores (primary outcome) fell 37% with the extract versus 19% with placebo (p = 0.003), and Athens Insomnia Scale scores improved more (p = 0.025). Hair cortisol was lower at week 8 (p = 0.025). During a laboratory stress test at week 8, salivary cortisol, salivary amylase, blood pressure and stress ratings were lower overall, but their change over the test did not differ between groups, and pulse did not differ. Mood (POMS), PROMIS-29, Restorative Sleep Questionnaire and Fitbit sleep measures did not differ from placebo.
Randomized controlled trial in 44 adults after total thyroidectomy for differentiated thyroid cancer, during radioiodine treatment. One group drank 180 mL of tea from a 2.0 g holy basil (Ocimum tenuiflorum) leaf teabag (ITANSE) after each meal for 4 days; the control group drank distilled water, so participants knew their group. The authors note the act of drinking tea may itself have affected anxiety. Funded by the Yamazaki Spice Promotion Foundation. The paper's title says basil tea, but the tea was holy basil. (Nomura et al. 2023, Heliyon)
44 adults undergoing radioiodine treatment (22 per group).
The rate of change in State-Trait Anxiety Inventory scores (state and trait) differed from water (p < 0.05): scores tended to fall with holy basil tea and rise with water. Saliva measures (cariogenic bacteria, ammonia, protein, occult blood) rose less with the tea, and salivary gland washout on scintigraphy was better preserved.
Randomized, parallel-group, open-label 8-week pilot trial: 250 mg tulsi extract capsule twice daily (500 mg/day) on an empty stomach versus no intervention (no placebo). Triglycerides, LDL, VLDL, BMI, plasma insulin and insulin resistance improved within the tulsi group only; the abstract reports no between-group tests for those. Authors report no financial conflicts. The 2017 systematic review lists occasional mild nausea in this trial. (Satapathy et al. 2017, Indian J Clin Biochem)
30 overweight or obese young adults (16 tulsi, 14 untreated control).
HDL cholesterol improved more with tulsi than in the untreated control (p = 0.037), the only between-group comparison reported. Liver enzymes (SGOT, SGPT) did not change.
Double-blind, randomized, placebo-controlled crossover trial of 300 mg/day ethanolic Ocimum sanctum leaf extract taken on an empty stomach for 4 weeks in 24 volunteers (22 completed). Primary outcome: interferon gamma and interleukin 4 in stimulated blood cultures. (Mondal et al. 2011, J Ethnopharmacol)
22 healthy adult volunteers who completed both periods.
Versus placebo, interferon gamma (p = 0.039), interleukin 4 (p = 0.001), T-helper cell percentage (p = 0.001) and natural killer cell percentage (p = 0.017) increased after 4 weeks. These are laboratory immune markers, not infection outcomes.