In this video, Motley Fool Health-Care Analyst David Williamson breaks down just what happened in the recent Canadian Supreme Court ruling against Pfizer (NYSE:PFE). The Canadian patent on the company's drug Viagra was due to expire in 2014, but the Court struck down the patent in a unanimous ruling, invalidating the patent. Williamson explains the losers and the winners in this situation, and just how much we can expect Pfizer to really be affected.

David Williamson owns shares of Pfizer. Follow him on Twitter @MotleyDavid. The Motley Fool has no positions in the stocks mentioned above. 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.