Worldwide, adverse drug reactions are a major cause of morbidity and mortality in patients, as well as increased healthcare costs. Published data show that there are around 2 million adverse drug reactions, including 100,000 deaths, which are established as the fourth leading cause of mortality. This culminates an estimated cost of 136 billion dollars to the global healthcare system. However, these values are underestimated, because in many parts of the world there are no reliable records of pharmacovigilance. This is the case in Latin America, where the records of adverse reactions are still insufficient, and therefore it is not possible to properly establish the extent of its effects on public health. At the same time, treatment failure due to sub-therapeutic levels of drugs is not evaluated in healthcare systems, especially in Latin America, where the "importation" of dosages and results from clinical trials form the fundamental basis of the application and acquisition of pharmaceutical products. This is due mainly to current protocols, which assume that patients are a single entity; therefore, drugs effective and well-tolerated in some patients are equally effective in the rest. Clinical experience shows that drugs that work well in some patients are ineffective or cause adverse reactions in others, and may even prove fatal to intolerant patients. The main objective of this book is to catalog the most relevant information concerning healthcare drug effects in Latin America. This could provide a huge benefit for Latin American patients, where it is estimated that there are plenty of side effects and treatment failure due to the "importation" of dosages and therapies regardless of population variability. It should encourage discussion and concern about the implementation and validation of pharmacogenomic testing and clinical guidelines for specific mixed populations of the region. It will also be valuable to demonstrate this research to health professionals (prescribers, insurers and regulators) in the region and the impact of pharmacogenomics on pharmacotherapy cost-effectiveness.