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.