Kava, the Liver and the Solvent Question
Kava, Piper methysticum, its six kavalactones, the flavokavains and pipermethystine, and how a move from cold water to ethanol and acetone extraction changed what reached the liver.
The episode reads the Institute's 2026 kava monograph. Kava is a sterile cultigen: it sets no viable seed, so every plant across Oceania for about 3,000 years has come from a stem cutting. The accepted name is Piper methysticum G.Forst.; material traded as Macropiper latifolium belongs to another species and is not kava. Vanuatu's Kava Act 2002 sorts the roughly 200 cultivars into noble, tudei and wichmannii groups and allows only noble kava for export and drinking. A common garden trial at the Waimanalo Research Farm in Hawaii grew two cultivars side by side for 3.4 years, and one carried about twice the kavalactones of the other. Strength follows the cultivar and the plant part; a Vanuatu origin speaks to legal standing and traceability.
On the clinical side, a Cochrane review of 11 trials and 645 people found a 5-point drop on the Hamilton anxiety scale, graded tier B, almost all of it from acetone or ethanol extracts such as WS 1490. Aqueous extracts gave mixed results in generalised anxiety disorder, including a 16-week Australian trial of 171 people that did not beat placebo, and Australian listed medicines may only use an aqueous extract of peeled root or rhizome, capped at 250 mg of kavalactones a day. The second half covers the 2000 to 2001 liver injury reports, a published Australian death, kava dermopathy in heavy traditional drinkers, four explanations for the liver cases (peelings, solvents, mould and tudei substitution), the three-month limit, pregnancy, alcohol, paracetamol and levodopa, six questions to put to a supplier, and a clonal crop in a changing climate.
In this episode: (00:00) Three thousand years of kava, then liver failure; (01:15) The Institute behind the monograph; (03:25) Piper methysticum, the intoxicating pepper; (04:21) A sterile clone kept alive by cuttings; (05:47) Peeled rootstock only; (06:30) G.Forst. or L.f.: a naming error in the trade; (08:55) Root scars, a fibrous fracture and a numb tongue; (10:30) Two hundred cultivars; (11:18) Vanuatu's Kava Act 2002: noble, tudei and wichmannii; (13:12) Rain, shade and three to five years in the ground; (14:53) The country-of-origin myth; (15:38) The Waimanalo common garden trial; (18:00) What a Vanuatu origin guarantees; (19:35) Six kavalactones; (20:28) Flavokavains and pipermethystine; (21:45) UHPLC and the chemotype code; (23:18) The kavain to flavokavain B ratio; (24:52) Cold water against ethanol and acetone; (26:20) Fifty times the flavokavains; (28:13) Liver cells in the dish; (29:42) The Cochrane review: 11 trials, 645 people; (31:46) Water extracts in generalised anxiety disorder; (33:16) The Australian irony: aqueous extracts only; (34:30) Trials that never named the chemotype; (35:55) The 2000 to 2001 liver reports; (37:07) An Australian death; (39:15) Pacific drinkers and kava dermopathy; (40:13) Four suspects: peelings, solvents, mould, tudei; (43:12) A perfect storm; (44:14) Australian limits: 250 mg, aqueous, peeled root; (45:41) Three months, pregnancy and alcohol; (46:30) Paracetamol and levodopa; (47:58) Six questions for a supplier; (51:23) A clone in a changing climate; (55:01) Closing.
Read more in the Institute's Journal: https://www.australian-pharmacognosy.org/pharmacopoeia/piper-methysticum/
Nothing in this episode is a prescription or a dose. If you want to use a herb, consult a degree-qualified herbalist with competencies and adequate training in pharmacognosy.
Dr Luke Iggulden, Chief Scientific Officer, made the episode from the Institute's Journal and monograph material. Jesse Kirby, Head of Community Outreach, wrote the show notes and chapters from the episode transcript.
The Herbarium Hour, from the Australian Institute of Pharmacognosy, Cardwell, Queensland.