We received the book The Rhodiola Reolution by Brown & Gerbarg....
they suggested to 2 clients with PD to also add Galanthus nivalis (snowdrop plant to their intake along with rhodiola and stated that it really made a huge difference in their lives. both were completely dependant upon their wives. They made a huge come back.
They also suggest a product called Clear Mind ( a blend of rhodiola, hydroxycinnamic acid from blueberries and Rhododendron caucasicum ) I have not researched any of these as yet, but the description in the book "before and after" are impressive.