The strange history of the EpiPen, the device developed by the military that turned into a billion-dollar business

The EpiPen is the latest drug facing drug-pricing pressure.

But it wasn't always this way.

The injectable delivers a dose of epinephrine, otherwise known as adrenaline, to treat extreme allergic reactions. It's been around for more than a century. And the pen that delivers the medication has been around since the 1970s, when it was first developed for the military.

Since 2007, the price for a two-pack has gone up from $93.88 to $608.61, an increase of more than 500%.

Here's the story of how a device that's now a household name became one of the most controversial drugs of 2016.