Most research data and clinical reports concentrate mainly on drug safety and little attention is paid on the inactive ingredients found in drug products. In fact, most patients and even some prescribers do not know what and which inactive ingredients are available in the drug products they take and prescribed and may not even be sure where to find information about them. According to FDA, An inactive ingredient is defined as any component of a drug product other than the active ingredient. Inactive ingredients are added to drug formulations to play vital roles in the preparation of various dosage forms and in the optimization of in vivo stability, dissolution, absorption and hence therapeutic efficacy of drugs. While inactive ingredients play important roles in drug formulations, a good number of them have the potential to cause adverse reactions. Recent study have shown that many of the most frequently prescribed oral medications in the United States contain at least one ingredient that could cause an adverse reaction. The study looked at more than 42,000 oral medications and identified more than three dozen inactive ingredients that have been described in medical literature to cause allergic symptoms following oral exposure. This review aims to highlight the potential pharmacovigilance implicat that inactive ingredients may have, and focus on increasing prescribers and patient’s awareness of the fact that some inactive ingredients can be quite active and can cause annoying symptoms or worse. In addition, the review emphasizes that more clinical trials and more research are needed to know how many patients are affected and ways of avoiding such adverse reactions. © RJPT All right reserved.