nefferdun - I can only encourage you to additionally grow some houttuynia if you can / have a garden - you have some fresh then also.
The chinese or vietnamese species has much higher level of the antiinfammatory substance (mentioned in link); this herb grows very drastic + rapid whereever it can get; I was told not to use artificial fertilizer b/c this may make the plants store more water in them (and look pimped up) but does not necessarily mean they have more of the substances we would like to have them for; they are good in salats, you can dry them for tea and can also use some of their roots;
I found this link useful for detailed info about
which species of the plant to get and what is in them: http://www.uni-graz.at/~katzer/engl/Hout_cor.html
good luck! dorit