Benefits
Traditional use to increase urine flow and flush the urinary tract
Europe's herbal committee accepts Java tea as a traditional herbal medicine to increase the amount of urine and flush the urinary tract in minor complaints, provided enough fluid is drunk. That acceptance rests only on long-standing use: its assessors judged the clinical data insufficient for a well-established use and could not identify any constituent with known therapeutic activity.
Urine volume in controlled studies of healthy volunteers
In a double-blind, placebo-controlled crossover study of healthy volunteers, Java tea did not change 12- or 24-hour urine output or sodium excretion; the EMA assessment report describes 40 people given 10 g of leaf as a decoction over one day. It also reports that 6 healthy men who drank four cups in a day had no change in urine volume versus a water-only day. Reported increases come from self-administration studies in 1927 and 1928.
Urine acidity and mineral excretion in healthy volunteers
In a small Thai study in healthy volunteers, the authors reported that urine became more alkaline after drinking Java tea while urinary oxalate excretion rose, a change they considered unfavorable. All values stayed within normal limits. Europe's assessors judged the effect on urine pH insufficient, from a medical point of view, to support a separate traditional use for kidney gravel, which needs medical supervision.
Symptom scores in a 14-day placebo-controlled trial
In a Thai trial of 76 adults with kidney stones and chronic complaints such as back pain, muscle pain and indigestion, capsules equal to 3.2 to 3.6 g of leaf a day for 14 days roughly halved summed symptom scores. Placebo did the same, and the difference between groups was not significant. Both groups were also asked to avoid purine-rich foods.
Blood pressure in multi-ingredient formulas
Java tea has been tested for blood pressure only inside combination products. In 60 adults with high-normal or mildly raised blood pressure, 8 weeks of a supplement with magnesium, Java tea, hawthorn and hibiscus lowered systolic pressure about 3 mmHg more than placebo. In a 30-patient study without placebo, a red yeast rice formula lowered 24-hour pressure from baseline only in the version with Java tea. Neither tested Java tea alone.
Urine samples tested against bacterial adhesion after a week of tea
In 20 healthy volunteers who drank 3 g of leaf as an infusion four times a day for 7 days, their urine reduced the ability of E. coli bacteria to attach to bladder cells in a laboratory test, but did not stop the bacteria from invading the cells. This is a lab measurement on urine samples with no placebo group, and it does not show that the tea prevents or treats any infection.
Mechanism of action
Electrolyte excretion in rats more than water output
In rats, oral Java tea extracts raised urinary electrolyte excretion, mainly sodium and potassium. One water extract did not raise urine volume, another gave a dose-dependent rise in urine with mostly potassium excreted, and a methanol-water extract increased urine volume only from the third day of repeated dosing. One study found it less potent than furosemide and hydrochlorothiazide. None of this has been reproduced in people.
Rosmarinic acid and sinensetin as quality markers
According to the EMA assessment report, European Pharmacopoeia grade Java tea must contain at least 0.3% rosmarinic acid; earlier editions used sinensetin (at least 0.05%). The leaf also holds methoxyflavones such as sinensetin and eupatorin, orthosiphol diterpenes and about 3% potassium. In rats, oral bioavailability was low (9.4% for sinensetin, 1.0% for eupatorin), and Europe's herbal committee recognized no active marker.
Methylripariochromene A in animal and tissue studies
Methylripariochromene A, a chromene isolated from the leaves, increased urine volume and sodium, potassium and chloride excretion in rats after an oral dose, relaxed isolated rat aorta and lowered blood pressure when injected under the skin of hypertensive rats. These are animal and tissue findings only.
Shifting E. coli toward a less adhesive form
Lab and animal work links Java tea's polymethoxylated flavones to reduced adhesion of uropathogenic E. coli. In urine collected after a week of tea drinking, bacteria switched on a motility gene and became more motile, which the researchers propose makes them less able to stick to bladder cells. This is an ex vivo laboratory finding.
Clinical trials
Placebo-controlled, double-blind crossover study of four traditional Vietnamese diuretic herbs, including Java tea, tested individually and in combination under standardized conditions. (Doan et al. 1992, J Ethnopharmacol)
Healthy volunteers in Vietnam. The European Medicines Agency assessment reports 40 volunteers given 600 ml of a decoction equal to 10 g of dried Java tea leaf, as three 200 ml doses 4 hours apart.
Java tea had no influence on 12- or 24-hour urine output or on sodium excretion, and neither did corn silk, Imperata cylindrica or Plantago major. The authors called for a critical review of herbal diuretic recommendations based on tradition alone. The abstract does not give the dose or sample size; those come from the EMA summary.
Study in healthy volunteers of urinary stone promoters and inhibitors after drinking Java tea, supported by a Mahidol University medicinal herbs fund. (Nirdnoy et al. 1991, J Med Assoc Thai)
Healthy volunteers in Bangkok, Thailand. The EMA assessment describes 6 men who drank four 250 ml cups of a decoction (5.3 g of leaf per liter) 6 hours apart on one day, compared with a water-only control day.
The authors reported more alkaline urine, which they thought might discourage uric acid stones, and higher urinary oxalate, which could raise stone risk. The EMA assessment reports no change in urine volume or electrolytes. All values stayed within normal limits, and the authors cautioned that results in healthy people may not apply to people who form stones.
Randomized, double-blind, placebo-controlled trial of a crude Java tea extract in capsules equal to 1.6 to 1.8 g of dried leaf, taken twice daily for 14 days. (Premgamone et al. 2009, Evid Based Complement Alternat Med)
76 analyzed adults in Northeast Thailand with kidney stones, at least two active chronic complaints (such as muscle or back pain, joint pain, indigestion, headache or fatigue) and no white cells in the urine; 36 on Java tea and 40 on placebo.
Summed symptom scores fell from 185.6 to 94.7 on Java tea and from 196.1 to 89.6 on placebo, with no significant difference between groups, so the primary outcome was null. Both groups were asked to avoid 25 purine-rich foods and ate fewer of them. Four people assigned to Java tea dropped out citing adverse effects: dizziness, myofascial pain, fatigue and palpitations.
Before-and-after study without a placebo group, testing urine collected before and during 7 days of Java tea intake against uropathogenic E. coli in laboratory assays. (Deipenbrock et al. 2023, Planta Med)
20 healthy volunteers who drank an infusion of 3 g of European Pharmacopoeia grade leaf four times a day for 7 days; urine was collected on day 1 (before tea) and on days 3, 6 and 8.
Pooled urine samples significantly reduced bacterial adhesion to human bladder cells on days 3, 6 and 8, did not affect bacterial invasion of the cells, and slightly reduced bacterial growth over 24 hours. Urinary Tamm-Horsfall protein did not change. The study measured lab effects of urine, not infections or symptoms.
Randomized two-arm study of a combination of policosanol, red yeast rice extract, berberine, folic acid and coenzyme Q10, with or without Orthosiphon stamineus, for 4 weeks, assessed by 24-hour ambulatory blood pressure monitoring. (Trimarco et al. 2012, High Blood Press Cardiovasc Prev)
30 patients with grade 1 essential hypertension and low cardiovascular risk, after a run-in period.
Mean 24-hour systolic and diastolic blood pressure fell significantly from baseline only in the arm that included Java tea; the formula without it did not significantly lower blood pressure. The abstract reports changes from baseline within each arm and no Java tea dose, there was no placebo, and the study was small.
Randomized, placebo-controlled trial of two pills a day of Diuripres, a supplement with magnesium and standardized extracts of Java tea, hawthorn and hibiscus, for 8 weeks after a 4-week low-fat, low-sodium Mediterranean diet run-in. (Fogacci et al. 2023, Phytother Res)
60 adults in Italy with high-normal blood pressure or stage I hypertension.
Systolic blood pressure fell 3.1 mmHg more than placebo at 4 weeks and 3.4 mmHg more at 8 weeks. At 8 weeks, diastolic pressure (3.8 mmHg), aortic pressure (5.2 mmHg) and hs-CRP also fell more than with placebo. The effect of Java tea cannot be separated from the other three ingredients.