ADRs are now recognized as the fourth leading cause of death in the United States after heart disease cancer and stroke. An important aspect of knowledge about ADRs is their prevention. A good example that can be cited to highlight the importance of prevention of ADR is the avoidance of aminoglycosides in renally compromised patients to prevent further nephrotoxicity. Moreover providing ADR-related information to the patient prior to starting drug therapy can avoid anxiety in the patient e.g. appearance of red coloured urine in patients consuming rifampicin. In certain conditions ADRs of 2 drugs can be utilized for gaining therapeutic advantage e.g. the combined use of hydralazine with a diuretic as former causes sodium retention while the latter enhances sodium excretion.