Benefits
Traditionally used to support urinary tract and bladder comfort
Buchu leaf tea and tincture were a Khoisan and Cape settler remedy for bladder and kidney complaints, and the leaf sat in European and American pharmacopoeias as a urinary herb for more than a century. That is a long history of use, not proof: no controlled human trial has tested oral buchu for urinary health.
Urinary antibacterial activity is weak in lab tests
Buchu's traditional reputation rests on antibacterial action in the urinary tract. In laboratory tests the essential oil showed very low activity against E. coli and Staphylococcus, water and ethanol extracts did not stop E. coli, and only a methanol-dichloromethane lab extract, unlike any tea or tincture, reached moderate activity, at milligram-per-milliliter concentrations. It is not a substitute for an antibiotic.
Kidney support claims have not been tested in people
A nephrology team auditing 184 supplement websites aimed at people with kidney disease found buchu among the ten most promoted plants and concluded these herbs were not adequately studied in humans. Germany's Commission E likewise declined to recommend buchu. People with kidney disease should not use it without their nephrologist.
Smooth muscle relaxing effect in isolated tissue
In guinea-pig intestinal tissue, buchu essential oils caused initial contraction followed by relaxation at high concentrations, apparently through cyclic AMP and, for A. betulina, calcium channel blockade. Early 1800s use of buchu for spasmodic urethral and bladder complaints fits this picture, but the effect has only been shown in an organ bath, never in a human bladder.
Blood sugar and weight findings are limited to rats
Work linked to a company selling a buchu-water extract reported normalized glucose in less severely diabetic rats and lower glucose in the rest and less weight and abdominal fat gain on a high-fat diet. Reviewers noted the extract's composition was undisclosed, no other lab has confirmed the results, and no human trial exists, so these remain animal findings only.
Mechanism of action
Diosphenol and sulfur aroma compounds
Buchu leaf oil is dominated by isomenthone, limonene, diosphenol and menthone. Diosphenol and the sulfur compound 8-mercapto-p-menthan-3-one give the blackcurrant note that makes the oil valuable to the flavor industry, which is where most buchu is used today.
Pulegone content depends on the species
Pulegone made up about 2 to 8 percent of commercial A. betulina oil in EFSA's batch analyses, while chemotaxonomy studies summarized by reviewers found roughly 32 to 73 percent in A. crenulata oil. Pulegone dissolves poorly in water, so leaf tea carries less than the oil, though not none.
Liver toxicity through menthofuran and glutathione loss
Human liver enzymes CYP2E1, CYP1A2 and CYP2C19 convert pulegone to menthofuran, which is oxidized further to reactive products. Glutathione normally neutralizes these; when it runs low, liver injury rises sharply, about tenfold in rats pretreated to deplete glutathione.
Citrus-type flavonoids in the leaf
Hesperidin, diosmin and rutin are the leaf's non-volatile marker compounds and help explain antioxidant readings in test-tube assays. In the rat buchu-water studies these flavonoids were present at tiny concentrations, too low to explain the effects reported.
Clinical trials
Narrative review of the historical, chemical, laboratory and animal research on Agathosma betulina and A. crenulata (Brendler T, Abdel-Tawab M 2022, Front Pharmacol 13:813142, PMID 35197854).
No human participants; the reviewers found no clinical trial of oral buchu.
The authors concluded that pharmacological studies to date failed to confirm buchu's traditional use and that any health claim needs randomized, placebo-controlled trials. The only placebo-controlled human study they located tested a topical buchu oil gel on exercise muscle soreness in 30 men and appeared as a research-unit report, so it says nothing about oral use. The first author consults for industry and is part-time employed by the herbal company Traditional Medicinals.
Laboratory study of A. betulina and A. crenulata essential oils on isolated guinea-pig ileum and on bacterial and yeast cultures (Lis-Balchin M, Hart S, Simpson E 2001, J Pharm Pharmacol 53(4):579-82, PMID 11341377).
No human participants; isolated animal tissue and microbial cultures.
Both oils caused initial contraction and then relaxation of intestinal smooth muscle through a post-synaptic mechanism involving cyclic AMP, with apparent calcium channel blockade for A. betulina. Undiluted oil did not inhibit Enterococcus hirae or Pseudomonas aeruginosa and showed very low activity against E. coli and S. aureus, leading the authors to conclude the oils have little antimicrobial potential.
Structured evaluation of 184 websites marketing dietary and herbal supplements to people with chronic kidney disease (Vamenta-Morris H, Dreisbach A, Shoemaker-Moyle M, Abdel-Rahman EM 2014, Am J Nephrol 40(5):393-8, PMID 25376340).
Supplement websites scored by two independent reviewers; buchu was one of the ten most common plant ingredients.
28% of sites claimed to slow kidney disease progression, 60% did not advise consulting a doctor, and more than 90% gave no drug interaction, pregnancy or pediatric caution. The authors found that these plants, buchu included, had not been adequately studied in humans, and that the available animal studies for the group showed detrimental effects and potential drug interactions.
US National Toxicology Program gavage studies of pulegone, the liver-toxic constituent of buchu oil, lasting up to two years (National Toxicology Program 2011, Natl Toxicol Program Tech Rep Ser (563):1-201, PMID 21921962).
F344/N rats and B6C3F1 mice given 18.75 to 150 mg pulegone per kg body weight, 5 days a week, in the two-year arms.
Liver tumors increased in dosed mice, and bladder papilloma or carcinoma increased in high-dose female rats, alongside liver, kidney and nasal damage. In the two-week arm nearly all rats given 300 mg/kg or more died of liver toxicity. These exposures are far above anything a cup of leaf tea supplies, but they are why buchu oil should never be swallowed.