Allium sativum (Family Amaryllidaceae or Liliaceae) is used worldwide for various clinical useslike hypertension, cholesterol lowering effect, antiplatelets and fibrinolytic activity etc. Due tothese common house hold uses of Allium sativum, as a herbal supplements, and failure of patientsto inform their physician of the over-the-counter supplements they consume leads to drug-nutrient interactions with components in herbal supplements. Today these types of interactionsbetween a herbal supplement and clinically prescribed drugs are an increasing concern. In vitrostudies indicated that garlic constituents modulated various CYP (cytochrome P450) enzymes.CYP 3A4 is abundantly present in human liver and small intestine and contributes to themetabolism of more than 50% of commonly used drugs including nifedipine, cyclosporine,erythromycin, midazolam, alprazolam, and triazolam. Extracts from fresh and aged garlicinhibited CYP 3A4 in human liver microsomes. The in vivo effects of garlic constituents are foundto be species depended and the dosing regimen of garlic constituents appeared to influence themodulation of various CYP isoforms. Studies have indicated that the inhibition of various CYPsby organosulfur compounds from garlic was related to their structure also. Studies using in vitro,in vivo, animal and human models have indicated that various garlic constituents can be thesubstrates, inhibitors and or inducers of various CYP enzymes. The modulation of CYP enzymeactivity and expression are dependent on the type and chemical structure of garlic constituents,dose regime, animal species and tissue, and source of garlic thus this review throws light on thepossible herb drug interaction with the use of garlic.