Holy basil, sometimes called Thai basil tulsi, is an herb from the same family as the basil often used in cooking. Although it's used in Ayurvedic medicine, clinical studies backing up any of the traditional uses for this herb are limited. There aren't a lot of side effects associated with holy basil, but it isn't necessarily safe for everyone, so check with your doctor before taking it.
Use in Traditional Medicine
Traditional uses for holy basil include colds and other respiratory illnesses, headaches, fevers, heart disease and stomach disorders, according to the University of Michigan Health System.
An article published in the "International Journal of Pharmaceutical Sciences Review and Research" in December 2014 noted that holy basil is sometimes used for inducing sweat and alleviating indigestion and anorexia. It may also help thin the blood, prevent cataracts and arthritis, enhance memory and limit the risk for high blood pressure, inflammation, high cholesterol and asthma, according to the article. Further clinical studies are necessary to verify these effects, however.
Potential Health Benefits
A preliminary laboratory study, published in "Nutrition and Cancer" in 2013, shows that some of the beneficial plant chemicals found in holy basil may help with the prevention and treatment of cancer. They appear to help prevent damage to DNA and healthy cells from radiation, increase antioxidant activity, limit the spread of cancer cells and bring about cell death.
Preliminary animal studies have shown that holy basil may also be helpful for ulcers and lowering blood sugar, and it may have anti-bacterial and anti-convulsant effects as well, notes Drugs.com. Further research is necessary to verify it has these same effects in people, however.
Potential Adverse Effects
In the few clinical trials that have been done, holy basil has been well tolerated and didn't cause any significant side effects. An animal study published in the "International Journal of Ayurveda Research" in 2010, however, found that holy basil may decrease sperm count enough to prevent conception.
Holy basil may interact with barbiturates and blood thinners, increasing the effects of these medications. It may also interact with acetaminophen, potentially leading to liver damage. Pregnant women should avoid holy basil because it may be dangerous for the fetus. Holy basil appears to interfere with the formation of sperm and the implantation of embryos, according to the World Health Organization, so don't use it if you're trying to get pregnant.