My mistake, it's not the regeneration potion, it's the renewal potion.+++++++
The only way to get rid of the status effect "drained" (the one with the red droplet), is with a renewal potion, which can be purchased from Lord Braffit in Arnika (I think) and Fuzzfas in Trynton. It's very expensive, so I would avoid this condition as much as possible.