[jannet.duff]

Taking too many herbs, or even too much of the same herb can desensitise your estrogen receptors. Also, different herbs are weaker/stronger than others, you run the chance of your receptors getting the weaker herbs, and stopping the stronger herbs working.
As for taking different herbs ( outside of NBE ) I don't believe anyone has made a list of what not to take with what. You may find a summery on another site, ( Google ?? ).