systematic reviewEvidence: limited
Overview of human studies
24 human studies of tulsi (metabolic, cardiovascular, immune and neurocognitive outcomes), searched across Cochrane, Embase, Medline, PubMed, Indian databases and grey literature
The authors reported favourable clinical outcomes in all included studies and no significant adverse events, and concluded the findings support tulsi for lifestyle-related conditions. They also said more studies are needed on dose, dose form and which people benefit.[7, 16]
Limitations: Not a meta-analysis; no pooled effect size. It included books, theses and conference papers, and the abstract does not rate study quality. Authors are from the same RMIT group as the related 2014 review, whose author discloses consulting for a tulsi manufacturer. 'All studies favourable' is a sign of possible publication bias.
RCTEvidence: moderate
Stress and sleep
n=100 adults with stress, 8 weeks, 125 mg Ocimum tenuiflorum extract (Holixer) twice daily vs placebo
Compared with placebo, the extract was associated with greater improvement in Perceived Stress Scale (primary outcome) and Athens Insomnia Scale scores, lower hair cortisol at week 8, and lower salivary cortisol, salivary amylase, blood pressure and subjective stress after a laboratory stress test. No major adverse effects were reported.[8, 3, 4]
Limitations: A single branded extract; sleep tracker data did not confirm the sleep result and the authors call for gold-standard sleep measures.
RCTEvidence: limited
General stress symptoms
n=150 (71 extract, 79 placebo), 6 weeks, OciBest extract 1,200 mg of actives per day
Total self-rated stress-symptom scores fell more with the extract than with placebo, with the authors reporting about 39% more overall improvement. No adverse events were reported.[9, 3]
Limitations: Self-rated symptom scale; a commercial extract; we read the abstract only, not the full paper.
RCTEvidence: limited
Cognition in healthy adults
Healthy volunteers, 30 days, 300 mg ethanolic leaf extract daily vs placebo
Between-group differences favoured the extract on reaction time and error rate in Sternberg and Stroop tests and on P300 latency. Salivary cortisol and anxiety scores improved within the extract group only, not significantly between groups.[10, 3]
Limitations: Placebo group also improved on several tests; short; participants were healthy, so the findings say little about any condition.
otherEvidence: preliminary
Generalised anxiety
n=35, 60 days, 500 mg leaf-extract capsule twice daily, single-arm (no control group)
Anxiety, stress and depression ratings improved significantly from baseline. The authors suggested it may be useful in generalised anxiety disorder.[14, 3]
Limitations: No placebo or control arm, so changes cannot be attributed to the herb. Small and short.
RCTEvidence: preliminary
Immune markers
Crossover, 24 healthy volunteers (22 analysed), 300 mg ethanolic leaf extract vs placebo, 4 weeks
The extract group had higher levels of interferon-gamma and interleukin-4, and higher percentages of T-helper cells and NK cells, than placebo.[11]
Limitations: Laboratory markers in healthy people; no clinical outcome such as fewer infections was measured. Very small.
RCTEvidence: limited
Blood glucose in type 2 diabetes
Single-blind placebo-controlled crossover in people with non-insulin-dependent diabetes; holy basil leaves vs placebo leaves
Fasting blood glucose fell by 21.0 mg/dl (17.6%) and post-meal glucose by 15.8 mg/dl (7.3%) with holy basil compared with placebo; total cholesterol showed a mild reduction.[12, 4]
Limitations: Published 1996, single-blind, small, and done with leaves rather than a standardised extract. The Merck Manual says there are few high-quality human studies and mentions a 90-day trial of 60 patients adding holy basil to glibenclamide, which we did not open. Do not use as a substitute for diabetes treatment.
RCTEvidence: preliminary
Weight, lipids and insulin
n=30 overweight or obese adults, open-label, 8 weeks, 250 mg extract twice daily vs no intervention
The extract group improved on triglycerides, LDL, HDL, BMI, insulin and insulin resistance; HDL was also better than in the control group. Liver enzymes did not change significantly in either group.[13, 3]
Limitations: Open-label with no placebo and only 30 participants; most of the improvements were within-group changes.
RCTEvidence: preliminary
Oral health (mouthrinse)
60 children at high caries risk, three groups of 20, 7 days: 4% tulsi ethanolic extract rinse vs 0.05% sodium fluoride rinse vs black myrobalan rinse
Salivary pH rose and Streptococcus mutans counts fell in all three groups. The pH increase was larger with fluoride than with the herbal rinses.[15, 3]
Limitations: Short, small, a laboratory marker rather than cavities; a rinse, not an oral herb.
RCTEvidence: moderate
Gum health (mouthwash vs chlorhexidine)
Triple-blind RCT at Teerthanker Mahaveer Dental College, Moradabad: 108 volunteer students, tulsi mouthwash (n=36) vs chlorhexidine (n=36) vs saline (n=36), 30 days
Tulsi mouthwash reduced plaque and gingival bleeding scores significantly compared with saline at 15 and 30 days, and the authors found it as effective as chlorhexidine, the standard dental mouthwash.[23]
Limitations: Healthy students, one month, plaque and gum scores rather than tooth or gum loss; a rinse, not an oral herb.
RCTEvidence: limited
Gingivitis (mouthwash after scaling)
Double-blind RCT at Vishnu Dental College, Andhra Pradesh, published in AYU: 60 patients with gingivitis after scaling, tulsi vs aloe vera vs chlorhexidine mouthwash (20 each), twice daily for 30 days
At 30 days tulsi, aloe vera and chlorhexidine were equally effective in reducing plaque, gingival and bleeding indices; at 15 days the herbal rinses had not yet matched chlorhexidine.[24]
Limitations: Small, one month, no placebo arm in the final comparison.
otherEvidence: preliminary
Oral submucous fibrosis (topical)
Two Indian clinical studies without a control group: BHU Varanasi (41 patients, tulsi 1 g plus turmeric 1 g in glycerine, applied 3-4 times a day, 3 months) and KLE Belagavi (60 patients, topical tulsi paste, 3 months)
Both reported significant improvement in burning sensation and mouth opening over 3 months, and no systemic changes in blood tests in the BHU study.[25, 26]
Limitations: No control or placebo arm, so improvement cannot be attributed to tulsi alone; the BHU study combined tulsi with turmeric. Oral submucous fibrosis needs specialist care.
These studies explain possible mechanisms. They do not show the same effect in people.