Merck Manual

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Holy Basil


Laura Shane-McWhorter

, PharmD, University of Utah College of Pharmacy

Reviewed/Revised Jan 2023

Holy basil (Ocimum tenuiflorum), also known as tulsi, is a perennial plant that is native to the Indian subcontinent. It is closely related to the sweet basil plant widely used in cooking.


Holy basil is considered an adaptogen, which means it is thought to help the body respond to stress and restore normal function. Holy basil is used to

  • Reduce anxiety and stress

  • Lower blood glucose in people with diabetes

  • Lower cholesterol levels

  • Provide protection from bacterial and viral infections

  • Promote wound healing

  • Reduce inflammation

Holy basil seems to be safe for most people when taken by mouth for up to 8 weeks. The safety of taking holy basil for longer than 8 weeks has not been studied.


There are no high-quality studies in people demonstrating that holy basil is effective for treating any health condition. Small studies have shown improvement in fasting and postprandial blood glucose and some evidence of hemoglobin A1C lowering in people with type 2 diabetes.

Adverse Effects

Holy basil can have adverse effects such as nausea or diarrhea.

Holy basil might not be safe when taken by women who are pregnant or trying to become pregnant. In animal studies, large doses of holy basil reduced the chance that a fertilized egg would become attached to the uterus and that the pregnancy would last for a full term. Whether these effects happen in humans is not known. The safety of holy basil in women who breastfeed their babies has not been studied.

Holy basil might decrease levels of the thyroid hormone thyroxine, worsening hypothyroidism.

Holy basil could increase the risk of bleeding during and after surgery, because it might slow down blood clotting.

Drug Interactions

Holy basil may decrease the efficacy of thyroid hormone drugs.

The effect of holy basil to slow down blood clotting may increase the risk of bleeding in people taking antiplatelet or anticoagulation drugs. Per animal data, holy basil may also enhance the sedating effects of barbiturates.

(See also table .)

NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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