Originally posted by Suzaku:

There are poison arrows, but they're not really worth it.

The Draugr Fang bow adds poison damage to any arrow fired from it.

The poison damage from dragur fang firing poison arrows stacks. That's the only kind of elemental damage that stacks. Later game you can craft ooze bombs. They are an AOE poison attack that doesn't affect you if you are the one that threw the ooze bomb.