The information provided here is not a replacement for a doctor. You shouldn't use it for the purpose of self-diagnosing or self-medicating but rather so you can have a more informed discussion with a professional TCM practitioner.
Because it is a herb specifically indicated to treat fasciolopsiasis as can be seen on Areca Nut's page.
Its main actions are: Destroys parasites. Regulates Qi circulation. Promotes urination.