Definition. Clinical pharmacology is the scientific discipline that involves all aspects of the relationship between drugs and humans. The term 'clinical pharmacologist' is also used in the professional sense to refer to those physicians who are specialists in clinical pharmacology. They have undertaken several years of postgraduate training in many aspects of the above relationship involving teaching, research and health care. Such clinical pharmacologists have as their primary goal that of improving patient care, directly or indirectly, by developing better medicines and promoting the safer and more effective use of drugs. b. Aims. This document aims to set the scene for clinical pharmacology in the early part of the 21st century following the concepts of an earlier report by the World Health Organization in 1970 . This document is aimed primarily at decision-makers in a variety of organizations, particularly in governments and their healthcare ministries, in addition to chief executives and board level directors of primary and secondary care systems and directors in pharmaceutical companies. We hope they will realize the great benefits that expertise in clinical pharmacology can bring to the delivery of better healthcare for all populations. c. Clinical care. Clinical pharmacology has developed a number of ways in which the clinical care of patients can be improved. The prime aim is to improve the rational use of drugs (RUD) both for individual patients and for patient populations wherever they may reside. The clinical pharmacologist will be expert in the critical evaluation of new and old therapies, and will use drug utilization studies and pharmacoepidemiological services to help in this task as well as skills such as pharmacogenetics. Clinical pharmacologists have an important role on Drug and Therapeutics Committees where they help the rational introduction and use of new and expensive medicines into the delivery of health care. Clinical pharmacologists will provide, in association with other healthcare staff such as pharmacists, drug information services to a wide variety of prescribers. Specialist services may include therapeutic drug monitoring (TDM), involvement in clinical drug toxicology and pharmacovigilance. Adverse drug reactions (ADRs) still cause many problems for patients, and healthcare systems could do more to prevent these as most of them are predictable through a knowledge of pharmacology. The concept of personalized medicine is one where drug therapy can be based on the pharmacogenetic characteristics of a particular patient. While in its infancy as a discipline, there are now good examples whereby adverse effects can be minimized and drug efficacy enhanced by a knowledge of the genetic make-up of patients. d. Research is a vital part of the training and everyday work of a clinical pharmacologist. The endeavour of a pharmacologist working in the clinical environment is to develop methods and strategies that improve the quality of drug use in individual patients and patient populations. Clinical pharmacological research has always been translational in the sense that the discipline aims to take new scientific data on drugs into rational patient care. Clinical pharmacologists could be even better equipped to undertake 'translational' research, especially the design and execution of the early phase of drug studies in humans (Phase 1). Too few contemporary clinical pharmacologists are actively engaged in the design, conduct and improvement of clinical trials. e. Teaching is a vital part of the work of a clinical pharmacologist. Although all doctors and many health care professionals need regular education concerning drugs, perhaps the most important area currently is the training of new prescribers which is primarily new physicians as pharmacists and nurses do comparatively little prescribing when looked at in a worldwide sense. The ability of new young physicians to prescribe safely and effectively has been criticized in recent years and new systems are being developed so that much more attention is paid to these skills in the training of medical students. As assessment drives learning, the assessment systems are being improved, too. Specialist training of clinical pharmacologists is addressed in Addendum II, as there is aworldwide shortage of such specialists. However, the needs, the resources and the regulatory arrangements available in different countries mean that the approach suggested is a general one. f. Pharmaceutical companies have been at the forefront of helping to train clinical pharmacologists. While many of the skills acquired in such companies are useful for the general training of a clinical pharmacologist (e.g. clinical trials), a long-term career in such a company requires a new set of skills for which training is needed. g. Governments need clinical pharmacologists to help deliver the goal of ensuring safe and effective drug therapy for their populations, whether the clinical pharmacologists are working in hospitals, regulatory agencies or in health technology assessment (HTA). With a few notable exceptions, the discipline of HTA has emerged in the absence of contributions from clinical pharmacology. This needs to change if HTA is to meet its full potential. h. Clinical pharmacologists have a crucial role to play in helping to deliver the WHO agenda of 'Guidelines for the Development of National Drug Policies' to which more than 150 countries are now signed up . The policies aim to ensure: the quality, safety and efficacy of medicines equitable access to medicines for all the population the rational/quality use of medicines a viable and responsible local pharmaceutical industry. Clinical pharmacologists could do much more to meet the health needs of those peoples who have in the past been marginalized. They include children, those with rare diseases, and those with conditions that are endemic in the poorest parts of the world. Training of clinical pharmacologists to meet these needs will have to be rather different from that envisaged in 1970 when the first WHO report was published .