Figure 1

Potential avenues of drug repositioning. Most repositioned drugs so far have been discovered through serendipitous treatment or unexpected side effects observed during clinical trials (path 1, path 6). More rational approaches to the identification of drug repositioning candidates involve finding existing drugs that can modulate specific disease phenotypes (path 2), finding new drug-target interactions (path 3), finding new roles for existing targets (path 4), or finding new pathways in disease (path 5). One or two examples of successfully repositioned drugs are listed for each method.