Any type of mushroom extract is typically and mainly used for immune system function. It apparently activates T cells and Natural Killer cells in the immune system to help fight infections and other problems found inside the human body. I have not read any studies that would show mushrooms having any treatment effect toward parasites, unless naturally by helping the immune system fight them off. Although in stronger infections this is rare.

Reishi is used for fungal infections and immune strengthening. For mild cases, you might feel some difference but it should be used together with synergestic herbs or meds. For systemic cases where also parasites are involved, these on their own, will not make much difference. I have taken turkey tail for fungus and i did have die off. I take shiitake for immune system.