Holy basil, also called tulsi, may help you lower your cholesterol and can act as an antioxidant, according to a study published in "Oxidative Medicine and Cellular Longevity" in 2011. You shouldn't use holy basil as a supplement without first consulting your doctor, however, because it can have adverse effects in certain people.
Potential Side Effects
Holy basil is generally recognized as safe in the United States and doesn't seem to cause a lot of side effects. People with diabetes need to take care because it may lower blood sugar, and those on blood thinners may need to adjust their medication dosage because holy basil can increase the blood-thinning effects of these drugs. A study published in the "International Journal of Ayurveda Research" in 2010 found that holy basil lowered sperm counts in rabbits, but it isn't clear whether it has this effect in people, too.
Holy basil may interact with certain medications, including barbiturates and acetaminophen. Avoid taking holy basil during pregnancy because evidence is conflicting on whether this is safe, with some reports noting it may bring on contractions, which could cause a miscarriage.