Pau D’arco is a natural blood thinner and psyllium husks are capable of causing small lacerations in the intestines. This is a potentially dangerous combination and has been known to send users to the emergency room with intestinal bleeding.
Of course, you might use it for six months and never have a problem.
But this is just one more example of companies producing products and having no idea of what the individual substances are and what they are capable of. But you may have the combination a hundred times without a problem.