The interdependent relationship between pharmacology and toxicology is fundamental to the concepts of efficacy and safety of both drugs and xenobiotics. The traditional concept of establishing efficacious and tolerated doses to define a 'therapeutic window' appears simplistic in the context of an exponentially increasing database on molecular mechanisms and cell biology that inform our understanding of homeostasis. Recent advances in nano medicine illustrate the convergence of efficacy and safety considerations that are central to establishing a clear pathway for regulatory review. The following overview considers biological responses to the administration of nanoparticles and the scale of balanced, within a range that might be considered 'normal', to unbalanced, abnormal responses associated with health and disease
