Japanese knotweed (Polygonum cuspidatum) is one of the world's most invasive plants nicknamed "Godzilla weed," Believe it or not it is form the Buckwheat Family and introduced from Japan to the West in the 1800’s.
Knotweed is used for bronchitis, cough, gum disease (gingivitis), and sore mouth and throat. It is also used for lung diseases, skin disorders, and fluid retention. Some people use it to reduce sweating associated with tuberculosis and to stop bleeding.
I feel it has gained much more popularity as a herb to treat Lyme Disease. It is a safe herb but I will say that less than 1% of patients experience loss of taste. I have had complaints of dry mouth and bitter taste in the mouth. Useful for Lyme is that it breaks up biofilms and inhibits biofilm formation. It is bacteriostatic and bacteriocidal.
I would encourage if you have Lyme Disease please read ‘ Healing Lyme’ by the foremost herbalist for Lyme, Stephen Harrod Buhner. Also try to see Sacred Science: Remedies Episode 5