There is a multibillion-dollar drug industry that could be witnessing the future of its demise. Counterfeit prescription drugs are a big business -- and a big problem for public health. And it looks like one big pharma has had enough.

To combat counterfeit drugs, Pfizer intends to sell Viagra online in what could be a game-changer for the entire industry. In this video, health care analyst David Williamson explains what it all means for investors.

Follow David on Twitter: @MotleyDavid.

David Williamson owns shares of Pfizer. The Motley Fool has no position in any of the stocks mentioned. 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.