Every time a drug is administered to the animal to treat an ailment, no matter whether it is acute or chronic manifestation, it usually goes together with some other prescription medicine, OTC (Over the counter) formulation, herbs or even food. All the xenobiotics such as drugs, toxins and food components as well as the endogenous compound that are formed in the animal body as a routine phenomenon exert a stimulatory or inhibitory effect on the different physiological and biochemical processes going in the body. These effects may alter the normal metabolism and/or drug transport or its efficacy drastically and thus expose the man and animals to the risk of a potentially dangerous interaction. The present review discusses these potential reactions and their mechanisms that help in navigating the hazardous combinations of drugs with other medicines, food, herbs, vitamins and minerals with confidence.