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Herb library · Herb · Ocimum tenuiflorum (syn. O. sanctum)

Holy basil (tulsi)

A sacred basil of India, grown at homes and temples and widely taken as a tea. Human studies are few, small and short; a 2017 review found them favorable for blood sugar and stress, and called for more research.

Traditional use

Native to the Indian subcontinent and revered in the Ayurvedic and Siddha systems. The leaf has been taken as a tea and used in many home remedies; the juice of the leaves was used as ear drops. Dutt's 1877 compilation from Sanskrit medical works records that the plant was grown and watered daily in every Hindu household as sacred to Vishnu, that rosary beads were made from its stems, and that physicians gave the leaf juice with black pepper for feverish colds and used the leaves in decoctions for cough. Two cultivars are usually named, Rama or Sri tulsi with green leaves and Krishna or Shyama tulsi with purplish leaves; a related species, Vana tulsi, grows wild. It is sold today for stress, blood sugar and general wellness.

What studies show

  • Limited

    Blood sugar and metabolic health: a 2017 systematic review found 24 human studies, all reporting favorable results for blood sugar, cholesterol and related measures. The studies varied widely in dose and form, the longest lasted 13 weeks, and the reviewers call for further research to confirm dose and who benefits.

  • Limited

    Stress, mood and thinking: some of the same small studies reported benefits for psychological stress and memory; there is not yet enough well-designed research to be sure.

Be careful of

Cautions

  • NoteIn the reviewed studies side effects were minimal; one trial reported mild, passing nausea. No study lasted longer than 13 weeks, so long-term safety has not been measured.
  • InteractionIn one study tulsi added to diabetes medicine lowered blood sugar further than the medicine alone. If you take diabetes medicine, talk with your clinician before adding it.
  • PregnancyPregnancy and breastfeeding were not studied in the reviewed trials. NCCIH advises talking with your clinician before using Ayurvedic products while pregnant or nursing.
  • NoteSome Ayurvedic preparations include metals. The FDA warns that this makes some Ayurvedic products potentially harmful, and a 2015 survey found high lead or mercury levels in some of the supplements tested.
  • Ask a clinicianTalk with a clinician or pharmacist before using this if you take prescription medicines, are pregnant or breastfeeding, or are giving it to a child.

From the old books

What herbals and dispensaries of the past printed. History, in their words.

“The leaves are regarded as anti-catarrhal or expectorant and are used in catarrh, cough and pain in the sides.”
Udoy Chand Dutt, The Materia Medica of the Hindus (1877), p. 220. See the page of The Materia Medica of the Hindus, p. 220 (opens in a new tab) · Read the full passage from The Materia Medica of the Hindus, p. 220
“The Tulasi plant is venerated in India by the Hindus like the Vervein was amongst the Romans.”
William Dymock, C. J. H. Warden and David Hooper, Pharmacographia Indica (1892), vol. 3, p. 86. See the page of Pharmacographia Indica, vol. 3, p. 86 (opens in a new tab) · Read the full passage from Pharmacographia Indica, vol. 3, p. 86
“Krishna, the popular incarnation of Vishnu, has adopted this herb for his cult, whence the name Krishna-tulasi.”
William Dymock, C. J. H. Warden and David Hooper, Pharmacographia Indica (1892), vol. 3, p. 87. See the page of Pharmacographia Indica, vol. 3, p. 87 (opens in a new tab) · Read the full passage from Pharmacographia Indica, vol. 3, p. 87

Sources

  1. The Clinical Efficacy and Safety of Tulsi in Humans: A Systematic Review of the Literature (2017) (opens in a new tab) · NIH · read September 25, 2026
  2. Ayurvedic Medicine: In Depth (opens in a new tab) · NCCIH · read September 25, 2026

Reviewed September 25, 2026.