Herbal Tea Research Limitations and Unanswered Questions
Why research cannot yet say whether most herbal teas work: tea versus extract, small and weak trials, mixed products, brewing differences and open questions.
Content last updated . This page has not been medically reviewed.
Safety first. Natural products can cause side effects and interact with medicines. Read herbal tea and extract safety before you use anything on this page.
Does herbal tea work? The honest answer
It depends on the plant, the preparation and the question, and for most herbal teas the drink itself has been tested in few, small or low-quality human studies. Where stronger evidence exists, it is often for an extract, not for a cup of tea. That is the pattern across the sources below, and it is why this library labels evidence tea by tea. Our research snapshot shows how much has been published for each tea; this page explains why those results are hard to interpret.What this means for the evidence labels you see here
- Insufficient evidence: fits chamomile and raspberry leaf for the uses EMA reviewed, where the committee found trials without a comparison or a lack of clinical studies. [5][6]
- Promising but limited: appropriate when small trials of the tea itself point one way, but the pool is small, as in the diabetes review. [3]
- No good evidence of benefit is used only when a source says so.
- Preclinical: applies to cell and animal work.
Positive-sounding results need the same checks as negative ones. A review of tulsi reports that all 24 human studies it found had favourable clinical outcomes, while also noting the lack of large or long-term trials. [9] We do not infer bias from that; we note that favorable small studies are not the same as settled evidence.
Questions that remain open
These are gaps we found in the sources. We did not find a source that settles any of them.- For which teas, if any, do randomized trials of the drink itself show a benefit that lasts?
- How much does the plant, plant part, steeping time and amount change the drink's content and effect?
- How safe are regular amounts over years, in pregnancy, in children and with common medicines? We did not find a source that answers this for herbal teas in general; see herbal tea and medicine interactions.
- Do tea trials in one country or tradition apply elsewhere? Study region was a source of difference in the diabetes meta-analysis. [3]
What a reader can safely do
Ask what form a claim is about, look for a trial of the actual drink, and read how to compare herbal teas and extracts. For study designs in general, see the Research Library's guide to evidence types and study designs. Tell a pharmacist or clinician which herbal teas you drink, especially before surgery or if you take regular medicines.Frequently asked questions
Why do so few studies test herbal tea itself?
The sources we read do not explain why. They show that where regulators found studies, they were often of extracts or powders, and that tea studies are few and small. [1][3]
Does "no evidence" mean a herbal tea does not work?
No. It means the question has not been answered well. For raspberry leaf, EMA noted a lack of clinical studies, which is a gap, not a negative finding. [6]
Can I trust a study that says a herbal tea lowers blood sugar?
Treat it as promising but limited. The 2025 meta-analysis found lower fasting glucose and HbA1c with herbal tea, but it pooled only 14 trials and called for more research. [3] Blood sugar is a lab marker, not a health outcome. Ask your clinician before changing anything related to diabetes care.
Are animal and lab studies useful?
They help researchers decide what to test, but they are not human results. NIH describes animal findings for tea that human studies have not confirmed. [10]
How can I tell whether the product I buy matches the product studied?
Often you cannot. Check the botanical name, plant part and form on the label, and remember that "standardized" does not guarantee consistency. [11] See quality testing and certifications.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
The main limitations, with examples
| Limitation | Example from the sources we read | Why it matters |
|---|---|---|
| The study tested a different form | EMA says a specific valerian ethanolic dry extract is backed by clinical studies, while root preparations used as herbal tea have traditional use only. [1] EMA's ginger finding for motion sickness is for ginger powder, and its summary lists solid or liquid forms to be taken by mouth, not tea. [2] | Results do not transfer between tea, tincture, capsule and extract. |
| Few, small trials | A 2025 meta-analysis of herbal tea (non-Camellia sinensis) in type 2 diabetes pooled 14 randomized trials with 551 participants in total, and the authors said more research is needed given the limited number of studies. [3] | Small pools can be overturned by a new trial. |
| Weak methods | A systematic review of Chinese herbal tea for chronic simple pharyngitis found 6 randomized trials of low methodological quality, none with blinded outcome assessors, and could not draw credible conclusions. [4] | Poor design can make a treatment look better or worse than it is. |
| No comparison treatment | EMA noted that in the chamomile studies it reviewed, chamomile was not compared with any other treatment. [5] For raspberry leaf it noted a lack of clinical studies for the traditional uses. [6] | Without a comparison, a trial cannot tell whether the tea made the difference. |
| The control group changes the result | In the diabetes meta-analysis, the type of control (water, placebo or other) was a significant source of variation in cholesterol results. [3] | The authors concluded that water or placebo may be a more suitable control when judging antidiabetic effects of beverages. [3] |
| Mixed products | NIH says some chamomile studies used chamomile plus other herbs, making chamomile's own role hard to know. [7] | A blend result is not a single-plant result. |
| Studies are too varied to compare | The diabetes meta-analysis found that study characteristics, such as trial duration and region, explained differences in blood sugar results, and the teas were prepared with 2 to 20 g of plant material per day (a range in studies, not advice). [3] | Different plants, amounts and lengths cannot be treated as one "herbal tea". |
| Preparation changes the content | A review of yerba mate reports that caffeine concentration increased with brewing time in the studies it describes. [8] | The same leaf can give different drinks. |
| Long-term data are missing | The 2017 tulsi review notes the lack of large-scale or long-term clinical trials, even though it found 24 human studies. [9] | Long-term benefit and harm remain unknown. |
| Lab or animal findings are not human results | NIH reports that tea and tea polyphenols inhibited tumor growth in animal studies, but human studies have been inconclusive. [10] That statement is about true tea (Camellia sinensis), and it shows the general gap. | Cell and animal findings are labeled preclinical here. |
| "Standardized" does not mean consistent | NIH says a manufacturer's use of terms like "standardized," "verified" or "certified" does not necessarily guarantee quality or consistency. [11] | A study product may not match a shop product. |
References
- European Medicines Agency, HMPC. Valerianae radix (valerian root): herbal medicinal product, summary for the public. Read 2026-10-23.
- European Medicines Agency, HMPC. Zingiberis rhizoma (ginger rhizome): herbal medicinal product, summary for the public. Read 2026-10-23.
- Alasvand Zarasvand S, Ogawa S, Nestor B, Bridges W, Haley-Zitlin V. Effects of Herbal Tea (Non-Camellia sinensis) on Glucose Homeostasis and Serum Lipids in Type 2 Diabetes Mellitus: A Systematic Review and Meta-Analysis. Abstract read. 2025. Read 2026-10-23.
- Li C, Wu F, Yuan W, et al. Systematic Review of Herbal Tea (a Traditional Chinese Treatment Method) in the Therapy of Chronic Simple Pharyngitis and Preliminary Exploration about Its Medication Rules. 2019. Read 2026-10-23.
- European Medicines Agency, HMPC. Matricariae flos (matricaria flower): herbal medicinal product, summary for the public, EMA/490629/2015, 2016. Read 2026-10-23.
- European Medicines Agency, HMPC. Rubi idaei folium (raspberry leaf): herbal medicinal product, summary for the public, EMA/237849/2017. Read 2026-10-23.
- National Center for Complementary and Integrative Health (NIH). Chamomile: Usefulness and Safety. Read 2026-10-23.
- Gawron-Gzella A, Chanaj-Kaczmarek J, Cielecka-Piontek J. Yerba Mate: A Long but Current History. Nutrients, 2021. Read 2026-10-23.
- Jamshidi N, Cohen MM. The Clinical Efficacy and Safety of Tulsi in Humans: A Systematic Review of the Literature. 2017. One author discloses a consulting role with a tulsi manufacturer. Read 2026-10-23.
- National Center for Complementary and Integrative Health (NIH). Tea. Read 2026-10-23.
- National Center for Complementary and Integrative Health (NIH). Using Dietary Supplements Wisely. Read 2026-10-23.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.