I have been picking up some of the words for the shout "Marked for Death." I just noticed that I am getting the shout "Drain Vitiality" at the same time and the words are the same. So does Marked for death no longer work the way it did? This was my favorite shout for dealing with Dragons since it weakened their armor. But now if all it does it reduce their health, I will be disappointed. Marked for Death was especially useful when a dragon attacked a settlement since it helped the guards bring the beast down quicker with their wimpy arrows.

I think it is a new shout as you find drain vitality in the DLC areas

It's a bug, they are supposed to be separate.

I have two drain vitality shouts, one that has normal description and the other says something along the lines of "Drains heath, stamina, and magicka 1 point for twenty seconds."

yeah its a bug thats the shouts the dragon npcs use

Made me wonder why the cool down was 12, 12, 12. Though the shout cooldown times should be cut down anyways.

They're two separate shouts and what you encountered is a common bug.

Yea I ended up getting the glitched shout when I learned the last marked for death word of power in the Dark Brotherhood Sanctuary.