It is the zinc chloride that is caustic, not the bloodroot. The recommended dose of bloodroot is to teaspoons of powder in a glass of juice, twice daily. If you are not toxic, you will feel no ill effects. If you have what it eliminates, you will feel extremely nauseaus and exhausted. And you will have nightmares. Lower the dose and slowly work up. Can take years to reach the recommended dose if you have a lot of cancer or virus in you body. I have taken as much as 24 capsules in a day. I am still alive. Bloodroot will go after the diseased tissues without harming healthy tissues. Do not take bloodroot salve internally. The zinc chloride is caustic.

Internally bloodroot needs to be used with extreme caution.  On the skin it is caustic, and I have seen the effects of this with several people.

Other sources say the same thing:

http://ezinearticles.com/?Bloodroot-Plant-and-Bloodroot-Salve&id=4016117

"Each plant is a complex "chemical factory" and should be respected as such and approached with caution. Bloodroot sap is caustic."

http://hubpages.com/hub/Bloodroot

"Most of the active constituents of bloodroot is stored in the rhizome. This sap is very toxic. It contains morphine like compounds and also destroys animal tissue. It is traditionally used in herbal medicine as a component to ointments designed to destroy abnormal skin growths such as malinoma, warts and skin tags. This is an extremely painful process and can result in serious scarring if not done properly."

http://www.herbs2000.com/herbs/herbs_bloodroot.htm

"Both the powdered rhizome and the juice from bloodroot are extremely caustic, chemically capable of corroding and destroying tissue."

And many of the bloodroot pastes contain zinc oxide, which is not caustic.  In fact it is what they use to use for a sun screen and it is a major component of diaper creams.

Another fact that a lot of people do not realize is that the Native Americans came up with the original "black salve", which contained no bloodroot nor magnesium oxide.  It was the when the white man came along that they screwed with the recipe making a caustic compound by adding the bloodroot.