The following video is part of our "Motley Fool Conversations" series, in which health-care editor and analyst David Williamson and consumer goods editor and analyst Austin Smith discuss topics across the investing world.

The roller coaster ride for best-in-class multiple sclerosis drug Tysabri looks like it is coming to a satisfying conclusion for investors, and for about half the population struggling with MS. David and Austin discuss how a new test has changed the fortune of this drug, and its makers, in this video.

Austin Smith owns shares of Pfizer. David Williamson owns shares of Pfizer. The Motley Fool owns shares of Teva Pharmaceutical Industries. Motley Fool newsletter services recommend Quest Diagnostics, Elan, Pfizer and Teva Pharmaceutical Industries. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.