Kombucha (Fermented Tea)
Kombucha is sweetened tea, usually black or green, fermented by a SCOBY, a symbiotic culture of bacteria and yeasts that grows as a floating cellulose mat. Fermentation produces organic acids, giving a sour, often fizzy drink that keeps tea catechins and caffeine and can hold some alcohol. Starter cultures and finished products differ widely: nine commercial drinks varied in microbes, catechins, caffeine and alcohol (0% to 1.29%), and some have added probiotics. It is sold mainly as a drink, with powders and capsules also on the market, but the human trials tested drinks. Human research is recent and small. With a single high-GI meal, kombucha lowered the glucose and insulin response compared with soda water, but in people with type 2 diabetes it did not lower fasting glucose more than a placebo drink, and it did not add to weight loss on a reduced-calorie diet.
Benefits
Blood sugar and insulin response to a starchy meal
In 11 healthy adults, drinking 330 mL of live kombucha with a high-GI rice meal gave a glycemic index of 68 and an insulin index of 70, compared with 86 and 85 when the same meal came with soda water. A diet soft drink made no difference. This was a single-meal crossover test of one product.
Fasting blood sugar compared with a placebo drink
In a crossover trial in adults with type 2 diabetes, 240 mL of kombucha with dinner for 4 weeks lowered fasting glucose from baseline (164 to 116 mg/dL), while a sweetened placebo drink did not significantly (162 to 141). The difference between drinks was not significant, and only 7 people had complete glucose data.
Digestive comfort and bowel habits
In adults on a reduced-calorie diet, those also given 200 mL a day of green tea kombucha for 10 weeks reported fewer hard stools and less incomplete emptying than those on the diet alone. In 40 women with IBS, an inulin-enriched kombucha raised stool frequency over 10 days versus water, but the added fiber may explain it.
Gut bacteria composition
In healthy adults, a probiotic contained in a commercial kombucha and several short-chain fatty acid producing bacteria were more abundant after 4 weeks of drinking it. A kombucha with about 10 g of added inulin raised Bifidobacterium over 6 weeks versus unfermented tea, but the fiber may explain it. Green tea kombucha did not change gut bacteria versus diet alone. These are microbiome measures, not health outcomes.
Body weight and blood lipids during a reduced-calorie diet
In a 10-week trial in 59 adults with excess body weight, adding 200 mL a day of green tea kombucha to a reduced-calorie diet did not increase weight or fat loss, the stated primary outcome. Cholesterol and triglycerides fell from baseline only with kombucha, but changes did not differ significantly from the diet-alone group.
Oxidative stress and immune markers
In the same 10-week diet trial, green tea kombucha lowered blood hydrogen peroxide, a pro-oxidant marker, compared with diet alone, but other oxidative stress and blood vessel markers did not change. IL-6 rose in the control group compared with the kombucha group. These are blood markers, not measures of how people felt or functioned.
Mechanism of action
Organic acids from fermentation
Fermentation by yeasts and acetic acid bacteria such as Komagataeibacter produces organic acids, which lower the pH; nine commercial drinks all had a pH of about 3 to 3.2. One trial drink held lactic and acetic acids at under 1% each, and another listed glucuronic and gluconic acids as its main acids. Whether these acids explain the lower meal glucose response was not tested.
Live microbes that differ between products
One trial kombucha held lactic acid bacteria, acetic acid bacteria and yeasts at about 1 million CFU per mL each. Starter cultures fall into several distinct community types, and some commercial drinks have added probiotics such as Bacillus coagulans. In one trial, an added probiotic became more common in stool, but lasting colonization was not shown.
Tea polyphenols and fermentation compounds (lab and animal work)
Kombucha keeps tea catechins and caffeine, at levels that varied widely between nine commercial products. Antioxidant, liver and blood sugar effects proposed for kombucha come mainly from lab and animal studies, and reviews note that these effects still need testing in human clinical trials.
Clinical trials
Randomized, single-blinded, placebo-controlled crossover study using standard glycemic index methods; a rice-based meal with 50 g available carbohydrate eaten with 330 mL of soda water (control), diet lemonade or unpasteurized kombucha; registered ANZCTR 12620000460909; funded by an Australian Innovation Connections grant, with one author a consultant to the kombucha maker who helped design the study (Atkinson et al. 2023, Front Nutr)
11 healthy adults in Australia.
Glycemic index was 86 with soda water and 68 with kombucha (p = 0.041); insulin index was 85 versus 70 (p = 0.041). Diet lemonade did not differ from soda water (GI 84, II 81). The kombucha added 3 g of carbohydrate to the meal. This was a single-meal test of one product.
Randomized, double-blind crossover pilot; 240 mL of kombucha or an unfermented placebo drink (both sweetened with 10% sucrose and flavored with ginger) with dinner daily for 4 weeks each, separated by an 8-week washout; self-measured fasting glucose; registered NCT04107207; drinks donated by a kombucha brewer (Mendelson et al. 2023, Front Nutr)
Adults with type 2 diabetes in Washington, DC; 28 were randomized, 12 were analyzed and only 7 had complete glucose data.
Fasting glucose fell from 164 to 116 mg/dL on kombucha (p = 0.035) and from 162 to 141 mg/dL on placebo (p = 0.078). The primary comparison between drinks at week 4 was not significant (p = 0.265); a subset analysis that left out two people whose baseline glucose on kombucha was already under 110 mg/dL (5 people left) favored kombucha. One person reported bloating.
Randomized (2:1) controlled study without placebo; one 16 oz bottle a day of a commercial kombucha with added Bacillus coagulans, S. boulardii and Lactobacillus, or no drink, alongside a low-fiber Western-style diet; primary outcome gut microbiome composition; registered NCT06484504; funded by the kombucha maker (Ecklu-Mensah et al. 2024, Sci Rep)
Healthy adults in California; 30 enrolled, 16 kombucha and 8 control participants analyzed.
Blood biochemistry and inflammation markers did not change significantly across the cohort. Within the kombucha group, fasting insulin and HOMA-IR rose. Weizmannia, a probiotic in the drink, and several short-chain fatty acid producers were more abundant at the end. Diarrhea and bloating were reported by 31% of the kombucha group versus 12.5% of controls.
Randomized controlled parallel trial; a reduced-calorie diet alone or with 200 mL of green tea kombucha a day for 10 weeks; primary outcome weight loss and body composition; the control group had no drink (Fraiz et al. 2024, Nutrients)
59 adults aged 18 to 45 with excess body weight in Brazil who completed the trial (30 kombucha, 29 control).
Weight, BMI and body fat fell in both groups with no difference between them, so the primary hypothesis was not supported. The kombucha group lowered its lipid accumulation product (p = 0.029), IL-6 rose in the control group compared with kombucha (p = 0.023), and salivary microbial diversity increased with kombucha.
Analysis of the same randomized trial; 200 mL a day of green tea kombucha plus a reduced-calorie diet versus the diet alone, with intestinal permeability tests, gut microbiota sequencing, serum metabolomics and the Gastrointestinal Symptom Rating Scale; registered RBR-9832wsx (Fraiz et al. 2024, Foods)
59 adults with excess body weight in Brazil (30 kombucha, 29 control).
Intestinal permeability and gut microbiota did not differ between groups. At the end, the kombucha group had lower total symptom scores (p = 0.035), hard stools (p = 0.001) and feelings of incomplete emptying (p = 0.027) than controls. Participants knew their group because controls received no drink.
Analysis of the same randomized trial; a 500 kcal a day reduced diet alone or with 200 mL of green tea kombucha a day for 10 weeks, with blood oxidative stress and endothelial markers (Bonifácio et al. 2025, Br J Nutr)
Men and women aged 18 to 45 with excess body weight and no chronic disease (30 kombucha, 29 control).
Compared with control, kombucha lowered blood hydrogen peroxide (from 18.14 to 14.67 versus 16.5 to 15.09 micromol/mL; p = 0.007). The other oxidative stress and endothelial markers did not change.
Open-label randomized controlled pilot; 220 mL a day of a pasteurized, nonalcoholic kombucha drink enriched with inulin (2.53 g) and B vitamins, or water, for 10 days; registered NCT05164861 (Isakov et al. 2023, Curr Dev Nutr)
40 women with constipation-predominant IBS in Russia.
Stool frequency rose from 0.60 to 0.85 per day (p = 0.004) and Bristol stool scores from 3.0 to 4.4 (p = 0.001) with the kombucha drink, while the water group did not change significantly; the feeling of incomplete emptying also fell. The drink held added fiber and vitamins, so the effect cannot be credited to kombucha alone.
Randomized, double-blind, parallel trial; 250 mL a day of a kombucha with added chicory inulin (about 9.8 g per serving) or an unfermented, pasteurized sweetened tea control in identical packaging for 6 weeks; registered NCT06626997; financial support from the kombucha maker (Arce-López et al. 2025, Curr Res Food Sci)
60 healthy adults in Spain, of whom 58 completed.
The treatment effect on triglycerides was significant (p = 0.031), although the fall within the kombucha group (69.6 to 62.8 mg/dL) narrowly missed significance (p = 0.053). Bifidobacterium rose and Ruminococcus torques fell with kombucha, while species richness stayed stable. No correction was made for multiple comparisons, and the authors note the design cannot separate the effects of kombucha from those of the added fiber.
Side effects and drug interactions
Common Potential side effects
Important Drug interactions
Frequently asked questions about Kombucha (Fermented Tea)
What is kombucha, and what is a SCOBY?
Kombucha is sweetened tea fermented for days by a SCOBY, a symbiotic culture of bacteria and yeasts that forms a floating cellulose mat. In a study of 103 starter cultures used by commercial brewers, Brettanomyces yeasts and Komagataeibacter bacteria were the most common, but the cultures fell into several distinct types, so no two kombuchas are exactly alike.
How much research has been done on kombucha in people?
Very little until recently. A 2019 systematic review found only one human study. Since then, a handful of small trials, most with 60 or fewer people, have tested kombucha drinks for meal glucose, fasting glucose, gut bacteria, bowel habits and weight. Most claims about kombucha still rest on lab and animal studies.
Does kombucha contain alcohol or caffeine?
Usually some of both. Nine commercial drinks ranged from 0% to 1.29% alcohol and from about 15 to 113 micrograms of caffeine per mL. Alcohol can rise with continued fermentation in the bottle, and US rules treat kombucha at 0.5% alcohol or more as an alcohol beverage. Check the label if you avoid either.
Is a kombucha powder or capsule the same as the drink?
No. All of the human trials found used drinks, from 200 to about 473 mL a day, and drinks themselves differ widely in microbes, acids, sugar and caffeine. No trial tested a powder or capsule, so their effects are unknown, and results for one product do not carry over to another.
Is home-brewed kombucha safe?
Home brewing carries extra risks. The CDC investigated severe illness, including one death, in two people drinking home-brewed kombucha in 1995, although a cause was not proven, and lead poisoning has occurred when kombucha was brewed in a glazed ceramic pot. The CDC report advised against brewing or storing kombucha in ceramic or lead crystal containers and noted that about 4 oz a day may not cause problems in healthy people.
What is Kombucha?
Kombucha is sweetened tea, usually black or green, fermented by a SCOBY, a symbiotic culture of bacteria and yeasts that grows as a floating cellulose mat. Fermentation produces organic acids, giving a sour, often fizzy drink that keeps tea catechins and caffeine and can hold some alcohol.
What is Kombucha used for?
NutraSmarts does not list Kombucha under a health category. What the research covers: In 11 healthy adults, drinking 330 mL of live kombucha with a high-GI rice meal gave a glycemic index of 68 and an insulin index of 70, compared with 86 and 85 when the same meal came with soda water. A diet soft drink made no difference.
What is the recommended dosage of Kombucha?
The clinically studied dose is Drinks only: 330 mL with a single meal; 240 mL a day for 4 weeks; 200 mL a day of green tea kombucha for 10 weeks; one 16 oz (about 473 mL) bottle a day for 4 weeks; 220 to 250 mL a day of fiber-enriched versions for 10 days to 6 weeks. Always follow the product label and check with a healthcare provider for personal advice.
Does Kombucha interact with any medications?
Possible interactions include: Medicines that should not be combined with alcohol: kombucha can contain alcohol, at up to 1.29% in a survey of commercial drinks and 1.5% in one trial drink. Ask your pharmacist if your medicine carries an alcohol warning. If you take prescription medication, check with a pharmacist or doctor before using it.
How strong is the scientific evidence for Kombucha?
NutraSmarts rates the evidence for Kombucha as Limited (2 out of 5). It is backed by 8 study summaries and 16 cited references summarized on this page. A higher rating reflects more, larger, and better-designed human studies.
References(16 citations)
Evidence ratings on NutraSmarts are based on the totality of human clinical research, with emphasis on randomized controlled trials, meta-analyses, and systematic reviews. The references below directly support claims made throughout this page.
- Kombucha: a systematic review of the empirical evidence of human health benefit. Ann Epidemiol. 2019;30:66-70. doi: 10.1016/j.annepidem.2018.11.001.PubMedUsed to support: Systematic review of human research on kombucha. Searching PubMed, Scopus, Ovid, the NIH grant database and two trial registries in July 2018 (310 articles reviewed), the authors found only one study reporting empirical results in human subjects and no registered trials; the many claimed benefits came from non-human research.
- Microbial and Chemical Profiles of Commercial Kombucha Products. Nutrients. 2022;14(3):670. doi: 10.3390/nu14030670.PubMedUsed to support: Analysis of nine commercial kombucha products sold in the US. All had a similar acidity (pH 3 to 3.2) but differed widely in microbes, metabolites, tea catechins and antioxidant activity. Ethanol ranged from 0% to 1.29% and caffeine from about 15 to 113 micrograms per mL (the highest in a product with added green coffee bean extract). Bacteria were mainly Bacillus coagulans (added as a probiotic in some products) or fermenting bacteria such as Komagataeibacter and Gluconacetobacter, and yeasts were mainly Brettanomyces. DNA from gut-type bacteria such as E. coli was found in all nine, though viability and counts were not measured. One author sits on the scientific advisory board of a kombucha maker.
- Microbial Composition of SCOBY Starter Cultures Used by Commercial Kombucha Brewers in North America. Microorganisms. 2021;9(5):1060. doi: 10.3390/microorganisms9051060.PubMedUsed to support: DNA sequencing of 103 SCOBY starter cultures used by commercial kombucha brewers, mainly in North America. The most common and abundant microbes were the yeast genus Brettanomyces and the acetic acid bacterial genus Komagataeibacter, but cultures fell into four distinct community types, with other yeasts (Zygosaccharomyces, Lachancea, Starmerella) or lactic acid bacteria taking larger roles in some.
- Kombucha: A review of substrates, regulations, composition, and biological properties. J Food Sci. 2022;87(2):503-527. doi: 10.1111/1750-3841.16029.PubMedUsed to support: Review of kombucha substrates, composition, regulation and reported biological effects. The type and amount of sugar, fermentation time and temperature change the organic acids, vitamins, phenolics and alcohol in the drink, and the reported antioxidant, antimicrobial and antidiabetic effects still need clinical studies in people. The authors state that, because adverse reactions can occur, kombucha is contraindicated in infants, pregnant women, children under 4, people with kidney failure and people with HIV, and that regulations focus mainly on pH and alcohol content.
- Glycemic index and insulin index after a standard carbohydrate meal consumed with live kombucha: A randomised, placebo-controlled, crossover trial. Front Nutr. 2023;10:1036717. doi: 10.3389/fnut.2023.1036717.PubMedUsed to support: Randomized, single-blinded, placebo-controlled crossover study (ANZCTR 12620000460909) in 11 healthy adults. A standard high-GI rice meal (50 g available carbohydrate) was eaten with 330 mL of soda water (control), diet lemonade or unpasteurized kombucha. Glycemic index was 86 with soda water and 68 with kombucha (p = 0.041), and insulin index was 85 versus 70 (p = 0.041); diet lemonade did not differ from soda water. Funded by an Australian Innovation Connections grant; one author consults for the kombucha maker and helped design the study.
- Kombucha tea as an anti-hyperglycemic agent in humans with diabetes - a randomized controlled pilot investigation. Front Nutr. 2023;10:1190248. doi: 10.3389/fnut.2023.1190248.PubMedUsed to support: Randomized, double-blind crossover pilot study (NCT04107207) in adults with type 2 diabetes: 240 mL of kombucha or an unfermented, equally sweetened placebo drink with dinner daily for 4 weeks, with an 8-week washout. Of 28 randomized, 12 were analyzed and only 7 had complete glucose data. Fasting glucose fell from 164 to 116 mg/dL on kombucha (p = 0.035) and from 162 to 141 mg/dL on placebo (p = 0.078), but the week 4 difference between drinks was not significant (p = 0.265). The drink held lactic acid bacteria, acetic acid bacteria and yeasts at about 10^6 CFU/mL each, lactic and acetic acids under 1%, and 1.5% ethanol. Drinks were donated by a kombucha brewer.
- Modulating the human gut microbiome and health markers through kombucha consumption: a controlled clinical study. Sci Rep. 2024;14(1):31647. doi: 10.1038/s41598-024-80281-w.PubMedUsed to support: Randomized controlled study (NCT06484504) in healthy adults eating a low-fiber Western-style diet: a 16 oz commercial kombucha (with added Bacillus coagulans, S. boulardii and Lactobacillus) daily for 4 weeks (16 analyzed) or no drink (8 analyzed). The primary outcome was gut microbiome composition. Blood biochemistry and inflammation markers did not change significantly across the cohort; within the kombucha group, fasting insulin and HOMA-IR rose. Weizmannia, a probiotic present in the kombucha, and several short-chain fatty acid producing bacteria were more abundant at the end. The product was described as containing lactic acid (100 mg), acetic acid (75 mg), glucuronic acid (1,400 mg) and gluconic acid (650 mg). Diarrhea and bloating were reported by 31% of the kombucha group versus 12.5% of controls. Funded by a kombucha maker.
- Green Tea Kombucha Impacts Inflammation and Salivary Microbiota in Individuals with Excess Body Weight: A Randomized Controlled Trial. Nutrients. 2024;16(18):3186. doi: 10.3390/nu16183186.PubMedUsed to support: 10-week randomized controlled trial (59 completers) in adults with excess body weight on a reduced-calorie diet, with or without 200 mL of green tea kombucha a day. The primary outcome, weight loss, did not differ between groups: weight, BMI and body fat fell in both. The kombucha group lowered its lipid accumulation product (p = 0.029), IL-6 rose in the control group compared with the kombucha group (p = 0.023), and salivary microbial diversity increased with kombucha.
- The Impact of Green Tea Kombucha on the Intestinal Health, Gut Microbiota, and Serum Metabolome of Individuals with Excess Body Weight in a Weight Loss Intervention: A Randomized Controlled Trial. Foods. 2024;13(22):3635. doi: 10.3390/foods13223635.PubMedUsed to support: Same 10-week trial (registered RBR-9832wsx): 200 mL a day of green tea kombucha (n = 30) or no drink (n = 29), both groups on a reduced-calorie diet. Intestinal permeability markers and gut microbiota did not differ between groups. On the Gastrointestinal Symptom Rating Scale, the kombucha group had lower end-of-study total scores (p = 0.035), hard stools (p = 0.001) and feelings of incomplete emptying (p = 0.027) than controls; the authors reported no conflicts of interest.
- Effect of Green Tea Kombucha Within an Energy-Restricted Diet on Cardiometabolic Risk Markers in Individuals With Excess Body Weight: A Randomized Controlled Trial. J Food Sci. 2026;91(4):e71050. doi: 10.1111/1750-3841.71050.PubMedUsed to support: Same 10-week trial in 59 adults with BMI above 27 on a 500 kcal/day reduced diet, with or without 200 mL of green tea kombucha a day. Total cholesterol, LDL, VLDL, triglycerides and uric acid fell from baseline only in the kombucha group, but changes from baseline did not differ significantly between the kombucha and control groups for any marker in the whole sample. Men in the kombucha group had lower HbA1c than men in the control group (p = 0.010), a subgroup result.
- Effect of regular green tea (Camellia sinensis) kombucha consumption on oxidative stress and endothelial health in individuals with excess body weight: a randomized controlled trial. Br J Nutr. 2025;134(1):70-78. doi: 10.1017/S0007114525103838.PubMedUsed to support: Same 10-week trial in adults aged 18 to 45 with excess body weight and no chronic disease: a reduced-calorie diet alone (n = 29) or with 200 mL of green tea kombucha a day (n = 30). Compared with control, kombucha lowered blood hydrogen peroxide, a pro-oxidant marker (p = 0.007); the other oxidative stress and endothelial markers measured did not change.
- Evaluation of the Efficacy of Kombucha-Based Drink Enriched with Inulin and Vitamins for the Management of Constipation-Predominant Irritable Bowel Syndrome in Females: A Randomized Pilot Study. Curr Dev Nutr. 2023;7(12):102037. doi: 10.1016/j.cdnut.2023.102037.PubMedUsed to support: Open-label randomized pilot study (NCT05164861) in 40 women with constipation-predominant IBS given 220 mL a day of a pasteurized, nonalcoholic kombucha drink enriched with inulin (2.53 g) and B vitamins, or water, for 10 days. Stool frequency rose from 0.60 to 0.85 per day (p = 0.004) and Bristol stool scores from 3.0 to 4.4 (p = 0.001) in the kombucha group, with no significant change in the water group; the feeling of incomplete emptying also fell with kombucha. The added inulin means the effect cannot be credited to kombucha alone.
- Effect of fiber-modified kombucha tea on gut microbiota in healthy population: A randomized controlled trial (RCT). Curr Res Food Sci. 2025;11:101130. doi: 10.1016/j.crfs.2025.101130.PubMedUsed to support: Randomized, double-blind parallel trial (NCT06626997) in 60 healthy adults (58 completed) given 250 mL a day of a kombucha with added chicory inulin (about 9.8 g per serving) or an unfermented, pasteurized sweetened tea control for 6 weeks. The treatment effect on triglycerides was significant (p = 0.031), though the within-group fall in the kombucha group (69.6 to 62.8 mg/dL) narrowly missed significance (p = 0.053). Bifidobacterium increased and Ruminococcus torques decreased with kombucha, while species richness stayed stable in both groups; no correction for multiple testing was applied. The authors note the design cannot separate the effects of kombucha from those of the added fiber. Financial support came from the kombucha maker, which also produced both drinks.
- Unexplained severe illness possibly associated with consumption of Kombucha tea--Iowa, 1995. MMWR Morb Mortal Wkly Rep. 1995;44(48):892-3, 899-900..PubMedUsed to support: CDC report of two women in Iowa who drank home-brewed kombucha daily for about 2 months and developed severe illness with lactic acidosis; one died. Both cultures came from the same parent culture, which at least 115 other residents used without similar illness, and testing found no known human pathogens and 0.7% to 1.3% alcohol. A causal link was not established. The report said about 4 oz a day may not cause adverse effects in healthy people, that risks for people with health problems or heavy intake are unknown, and that brewing or storing kombucha in ceramic or lead crystal containers should be avoided.
- Lead poisoning from drinking Kombucha tea brewed in a ceramic pot. Med J Aust. 1998;169(11-12):644-6. doi: 10.5694/j.1326-5377.1998.tb123448.x.PubMedUsed to support: Case report of a married couple in Australia who developed symptomatic lead poisoning requiring chelation therapy after drinking kombucha brewed in a ceramic pot for six months. The authors proposed that acids in the tea leached lead from the pot's glaze.
- Kombucha TTB website (accessed 2026). 2026;Regulated commodities: beverage alcohol, kombucha page..SourceUsed to support: Official US government web page, not PubMed-indexed. Fermentation of sugar by yeast can give kombucha 0.5% or more alcohol by volume, at which point it is an alcohol beverage under federal law. Kombucha bottled below 0.5% becomes subject to these rules if continued fermentation in the bottle raises it to 0.5% or more.