This chapter explores the relationship between changes in strategy and environmental pressures within the UK Pharmaceutical Industry during a ten- year period. Two stable strategic time periods (SSTPs) were identified each of five years duration. Within each time period seven strategic groups were found but 11 out of 29 firms (37.9%) changed strategic groups membership during the period studied. The break between these two SSTPs was found to coincide with a sharp increase in the substitution of branded pharmaceuticals by cheaper parallel imports. A significant relationship was found between firms that changed groups and both their continent of origin and nationality. Firms whose home markets are more vulnerable to substitution were more likely to switch strategic groups. © 2011 Nova Science Publishers, Inc. All rights reserved.