Benefits
Lower alcohol intake in lab drinking sessions
In small placebo-controlled studies of heavy drinkers, a week of kudzu extract, a week of pure puerarin, or even a single dose taken a few hours earlier led people to drink fewer beers in a timed lab drinking session. In a 4-week outpatient study, young men reported fewer drinks per week and more alcohol-free days. Kudzu is not a treatment for alcohol use disorder.
Slower drinking without a stronger buzz
In these studies people took smaller sips and took longer to finish each beer, and their urge to drink did not change. A separate crossover study found kudzu did not change how intoxicated people felt or how alcohol affected balance and reaction time. Peak blood alcohol was unchanged, so the reason people drank less is still unknown.
Menopausal symptom scores studied with kudzu root extract
Evidence here is preliminary. A 3-month randomized trial in 127 postmenopausal women found kudzu root (about 100 mg isoflavones a day) did no better than no treatment on cholesterol or hormone levels, and the authors could not show a general health benefit. A 4-week open-label study in 50 women, with no placebo group, reported lower menopause rating scores.
Mechanism of action
Aldehyde dehydrogenase and amine pathways (proposed)
Laboratory studies suggest kudzu isoflavones, especially daidzin, act on mitochondrial aldehyde dehydrogenase (ALDH2), the enzyme that clears acetaldehyde, or on related amine pathways. The researchers behind the human trials describe this as a possible explanation; it has not been confirmed in people.
Not explained by stronger intoxication
One idea was that kudzu makes alcohol feel stronger, so people stop sooner. A placebo-controlled crossover study found kudzu did not change subjective intoxication, balance or reaction time. It produced a brief, slightly faster rise in blood alcohol at the higher alcohol dose and a larger heart rate response, but no change in peak level.
Weak estrogen-like activity
Daidzein, one of the kudzu isoflavones, has weak estrogen-like activity in animal studies. For that reason the 4-week alcohol study enrolled only men. This activity is the reason kudzu has been tested for menopausal symptoms, with little benefit shown so far.
Clinical trials
Randomized, placebo-controlled crossover trial with treatment order counterbalanced; each person took kudzu extract and placebo for 7 days before a beer session (Lukas et al. 2005, Alcohol Clin Exp Res)
Men and women who were heavy drinkers, each acting as their own control in a naturalistic lab setting.
After kudzu, people drank significantly fewer beers, took more and smaller sips, and took longer to finish each beer. The urge to drink did not change, and no side effects were reported.
Randomized, double-blind, placebo-controlled trial: 2 weeks baseline, 4 weeks of kudzu extract (250 mg isoflavones three times a day) or placebo, 2 weeks follow-up (Lukas et al. 2013, Psychopharmacology (Berl))
17 men aged 21 to 33 who were not seeking treatment, drank about 28 drinks a week and had a diagnosis of alcohol abuse or dependence.
Kudzu cut the number of drinks per week by 34 to 57 percent, reduced heavy drinking days and increased alcohol-free days. Craving did not change. There were no adverse events or changes in liver or kidney tests. Two authors hold a patent on the extract or a financial interest in its maker.
Double-blind, placebo-controlled crossover pilot study of 1,200 mg a day of puerarin for one week (Penetar et al. 2012, Drug Alcohol Depend)
10 healthy adult heavy drinkers with access to up to six beers in a 1.5-hour session.
People drank an average of 2.4 beers on puerarin and 3.5 on placebo. On placebo, four people drank five or six beers; on puerarin, nobody did. Sips were smaller and the gap before opening the next beer was longer.
Placebo-controlled, double-blind, between-subjects trial of one 2 g dose of kudzu extract (520 mg isoflavones) taken 2.5 hours before a 90-minute session (Penetar et al. 2015, Drug Alcohol Depend)
20 men, 10 per group.
The kudzu group went from 3.0 beers at baseline to 1.9 after the dose, while the placebo group went from 2.7 to 3.4. The kudzu group also drank more slowly.
Double-blind, placebo-controlled crossover study of kudzu extract (750 mg isoflavones a day for 9 days) followed by alcohol challenges (Penetar et al. 2011, Alcohol Clin Exp Res)
12 healthy adults who drank moderately.
Kudzu did not change how intoxicated people felt or alcohol's effect on balance and reaction time. Blood alcohol rose slightly faster for 10 to 15 minutes after the higher alcohol dose, with no change in peak level or clearance, and heart rate rose more.
Randomized trial of kudzu root (about 100 mg isoflavones a day), hormone replacement therapy or no treatment for 3 months (Woo et al. 2003, Menopause)
127 postmenopausal women aged 50 to 65 in Hong Kong.
Kudzu did not change cholesterol, LDL or hormone levels compared with no treatment; only hormone therapy lowered cholesterol. Both active groups scored better on some attention tests. The authors concluded the study could not show a health benefit of kudzu for postmenopausal women in general.
Open-label, randomized dose-finding study of five kudzu root extract regimens for 4 weeks, with no placebo group (Bihlet et al. 2021, Front Pharmacol)
50 postmenopausal women aged 45 to 60 with at least mild menopausal symptoms.
Menopause Rating Scale scores fell from baseline in four of five groups, and bone and cartilage breakdown markers fell most clearly in the group taking two capsules three times a day. Without a placebo group, these changes cannot be separated from expectation or time. The extract was well tolerated. Several authors work for the companies that ran the study.