Kava's actually been pulled from the shelves in some European countries
that regulate herbs due to human deaths.  Can't recall the particulars,
BUT if you go to the FML Archives at
http://listserv.cuny.edu/archives/ferret-search.html
and search on each of those herbs you will find multiple posts with very
useful info, including precautions, though it is always possible that
more has come out since the postings.  It's a very friendly search
engine.  Click on "search the archives" and go from there.  Try just the
year 2002 by typing in JANUARY 1 2002 AND DECEMBER 31 2002 to start and
put in KAVA OR WORT, skipping the rest of the boxes and the full names,
then have it search and you should get just what you are seeking...
 
[Moderator's note: To seach just year 2002 it's easiest to just put
"2002" (without the quotes) into the the "Since" box and leave the
"Until" box blank for now.  BIG]
 
There may also be some posts that may be useful at the Ferret Health
List's Complete Archives http://fhl.sonic-weasel.org/ though I can't
offhand recall this topic on the FHL.  (There were several health
questions from other folks today that would be well answered by using
that site, though, and some that would be well answered using
http://www.smartgroups.com/groups/ferrethealth or the links at
http://www.ferretcongress.org .)
[Posted in FML issue 4017]