Chasing growth leads most drug companies with a choice: Either come up with exciting new treatments to ease humanity's suffering (that takes years and lots of money) or buy companies that already have done so. Some drugmakers do both. Canadian drugmaker Valeant Pharmaceuticals (VRX) has a track record of aggressive acquisitions. Its latest was announced Sept. 3. Valeant will pay $2.6 billion for Medicis Pharmaceutical (MRX). The deal should bring