Prescription painkillers.

Light green is pretty much OxyContin and Vicodin. 

Of note: Pharmaceuticals, Unspecified, and Alcohol are way up since 1999.

By adding all those sub-categories up, imperfect as they may be, it's clear that the rate of reported overdoses the U.S. more than doubled between 1999 and 2010. About half of those additional deaths are in the pharmaceuticals category, which the CDC has written about before. Nearly three-quarters of the pharmaceuticals deaths are opioid analgesics—prescription painkillers like OxyContin and Vicodin. And while cocaine, heroin and alcohol are all responsible for enough deaths to warrant their own stripes on the chart, many popular illegal drugs—including marijuana and LSD—are such a tiny blip as to be invisible.

Speed kills...the most!  I wonder why the article makes no mention of methamphetamine.

Because meth rounds to zero compared with the other drugs above. 

It is included as part of the yellow bar above (psychostimulants) along with MDMA and caffeine (!).

I wonder what percentage of Pharmaceuticals are iatrogenic?

"Of or relating to illness caused by medical treatment"? Seems like a lot! Especially if you include side-effects of allegedly safe and harmless medications that don't actually do what they're supposed to do.