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Single-Ingredient Clinical Trials with Tulsi — Systematic Review of the Evidence

Reviewed: Jamshidi N, Cohen MM. The clinical efficacy and safety of tulsi in humans: a systematic review of the literature. Evid Based Complement Alternat Med. 2017;2017:9217567. doi: 10.1155/2017/9217567.

Tulsi (Ocimum tenuiflorum, syn. O. sanctum, Lamiaceae), also called holy basil, and East Indian basil (O. gratissimum) are aromatic culinary and medicinal herbs indigenous to India that have been used in the Ayurvedic traditional medicine system for more than 3,000 years. Tulsi includes two botanically and phytochemically diverse cultivars: Rama tulsi and Krishna tulsi. Tulsi and East Indian basil, which have similar traditional uses, can be distinguished from other Ocimum species by their bright yellow pollen, high levels of eugenol (among other phytochemical differences), and fewer chromosomes.

The Indian Materia Medica lists tulsi leaf extract as a treatment for bronchitis, rheumatism, and fever.1 Tulsi leaf extracts also traditionally have been used to treat epilepsy, asthma, hiccups, skin and blood diseases, parasitic infestations, neuralgia (facial nerve pain), headache, wounds, and inflammation, and to maintain oral health. The leaf juice has been used to relieve earache, and leaf infusions have been used for stomach and liver disorders. Preparations of the roots and stems are used to treat mosquito and snake bites, and for malaria. 

Since 2007, tulsi has been the subject of more than 100 scientific publications. In vitro studies suggest that tulsi leaf has adaptogenic, metabolic, immunomodulatory, antitumor, anti-inflammatory, antioxidant, hepatoprotective, radioprotective, antimicrobial, anticonvulsant, anxiolytic, and antidiabetic properties. In vivo, tulsi preparations have been shown to have anti-stress effects and to protect rats from stress-related cardiovascular changes. Human studies of tulsi leaf in multi-herb formulas previously have been reviewed systematically. This is the first critical systematic review of tulsi as a single-herb agent in human clinical trials, according to the authors.

The authors searched electronic databases from inception through November 2016 for human clinical trials of tulsi mono-preparations with at least one clinical outcome. Only English-language reports were included. Studies were excluded if they reported only on topical applications. After screening 1,553 reports, 31 met the inclusion criteria. Four papers were inaccessible, one reported on two independent clinical trials, and three publications were based on the same clinical trial, leaving 26 trials for review. (The abstract, article text, and flow chart state there are 24 trials, but the tables appear to list a total of 26 trials.)

Study Details

The reviewed trials included a total of 1,111 subjects (10-80 years of age) and ranged in duration from two to 13 weeks. Most trials included subjects with acute or chronic illnesses, and only three studies used healthy subjects. In addition, only three studies had 100 or more subjects.

The following tulsi preparations and dosages were used: aqueous leaf extract (300-3,000 mg one to three times daily), methanolic leaf extract (300-1,000 mg twice daily), whole plant aqueous extract (6-14 g daily), fresh leaf aqueous extract (10 g daily in four equal doses), and tincture (30 drops daily in three equal doses). Two studies described the species or variety of tulsi used (Krishna, the purple-leafed cultivar of O. tenuiflorum, for both), and all others referred to tulsi as O. sanctum. Four studies compared tulsi with other herbal preparations, including curry (Murraya koenigii, syn. Bergera koenigii, Rutaceae) leaves, neem (Azadirachta indica, Meliaceae), a wild rosemary (Rosmarinus sp., Lamiaceae) tincture, and spinach (Spinacia oleracea, Amaranthaceae) leaf powder.

Only eight studies had a placebo group. Studies were randomized controlled trials (RCTs), non-placebo-controlled trials, or did not include randomization or control information. Jadad scores (a scale that ranks the methodological quality of a study) were generally low (0-3 points), and only three studies had high scores (4-5).

Outcome measures included blood glucose levels (eight studies), lipid profiles (six studies), immune response (six studies), neurocognitive changes (four studies), mood (three studies), fatigue (two studies), uric acid levels (two studies), secondary symptoms of diabetes (one study), and “sleep problems” (one study). A majority of reports stated that no adverse events (AEs) occurred; one reported mild, occasional nausea; and the rest did not mention AEs.


Metabolic Conditions

Of the 17 studies on metabolic conditions, 10 assessed tulsi’s effects on blood glucose, lipids, and blood pressure in subjects with type 2 diabetes or metabolic syndrome, and only one reported on tulsi’s effects on clinical symptoms of type 2 diabetes. Six of the studies on metabolic syndrome were RCTs. In addition, one study reported on obesity, and two investigated uric acid changes in subjects with gout. Six of the studies on metabolic conditions were between 12 and 13 weeks long (the rest were shorter). Trials lasting 12-13 weeks showed more dramatic changes in fasting blood glucose and postprandial glucose levels than trials of four to five weeks. In one study, hemoglobin A1c, a marker for blood glucose levels, significantly decreased with tulsi and hypoglycemic medication (the active comparator) compared to the medication alone. In studies of both healthy subjects and subjects with diabetes, there were significant improvements from baseline in fasting blood glucose, postprandial glucose, urine glucose, uric acid levels, and lipid profiles for those in the tulsi groups. Improved blood pressure was reported in some but not all studies. Improved body mass index was reported in obese subjects. 

Immune Response and Inflammatory Conditions

Five studies reported enhanced immune response in subjects taking tulsi. Two studies included patients with acute viral infections, one involving encephalitis and the other hepatitis. In the study on encephalitis, subjects taking the tulsi preparation demonstrated higher survival rates after four weeks compared to those taking dexamethasone. In the hepatitis study, subjects in the tulsi group reported symptom relief after two weeks compared to baseline. In patients with asthma, tulsi improved vital capacity and relieved symptoms in three days.

Mood and Cognition

Four studies on neurocognitive effects reported significant improvements in mood and/or cognition for those who consumed tulsi regardless of their age or gender, or of the formulation or dose used. In three studies, there were significant reductions in anxiety and stress for those who consumed higher tulsi doses for longer periods.


The authors concluded that the reviewed studies “suggest that tulsi is a safe herbal intervention that may assist in normalizing glucose, blood pressure and lipid profiles, and dealing with psychological and immunological stress.” Tulsi’s effectiveness across diverse clinical domains suggests an adaptogenic effect. The Ayurvedic tradition of consuming tulsi daily (either on an acute or a chronic basis) may be an effective lifestyle measure to combat stress-related chronic illnesses. More and better-designed RCTs are needed.

—Mariann Garner-Wizard


  1. Nadkarni KM, Nadkarni AK. Indian Materia Medica with Ayurvedic, Unani-Tibbi, Siddha, Allopathic, Homeopathic, Naturopathic & Home Remedies. Vol 2. 3rd ed. Mumbai, India: Popular Prakashan Private Ltd; 1982.