I suppose. I'm not sure exactly.

[it just happens? He doesn't really know quite how immunology works...]

Not difficult, no. Some things need to be steeped longer or shorter, or at lower temperatures, or stoppered up in different alcohols. But the basic ideas are the same; it isn't much trouble to adapt.

There's no harm in checking your herbs - it's usually relatively easy to tell based on how they look or feel.