Guides
Understanding Evidence Levels (A, B, C and T)
Hearing that "a study exists" for a herb does not mean it has been proven to work in people. On Herbadex, every benefit statement is tagged with one of four evidence levels.
Updated: October 15, 2026
A — Strong clinical evidence (Well-established use)
Uses backed by well-designed human clinical trials and, where applicable, an EMA "well-established use" assessment.
Examples include senna leaf for short-term constipation, psyllium husk as bulk-forming fibre and ginger for motion-sickness nausea.
B — Limited clinical evidence
Small human trials or preliminary meta-analyses suggest a possible benefit, but sample sizes or study quality are limited.
These findings are promising but do not replace standard medical care.
T — Traditional use
The most common category in EMA monographs. Efficacy is not proven by clinical trials, but plausible on the basis of at least 30 years of documented use (including at least 15 years in the EU).
Chamomile, linden, lemon balm and fennel teas for colds or mild digestive upset fall into this category. "Traditional" does not mean useless; it means the basis is long experience rather than clinical trials.
C — Laboratory or animal evidence only
Effects seen only in cell cultures (in vitro) or animal experiments. An effect in a test tube does not prove that drinking a tea produces the same effect in the human body.
For this reason, Herbadex never promotes level-C findings as primary benefits.
Frequently asked questions
What is the main difference between Traditional use (T) and Clinical evidence (A/B)?
Clinical evidence (A/B) comes from controlled human studies, whereas Traditional use (T) rests on at least 30 years of documented safe use without requiring clinical trials.
Why do test-tube (C) studies not prove a benefit in people?
A compound applied directly to cells in a dish may be broken down during digestion or never reach human tissues in the same concentration.
Does level-A evidence mean a herb is free from side effects?
No. Evidence level describes how well an effect is studied, not whether the herb is risk-free. Level-A herbs such as senna and St John's wort still carry important warnings.
Sources
- European Union herbal monograph on Matricaria recutita L., flosEMA HMPC · 2015
- European Union herbal monograph on Zingiber officinale Roscoe, rhizoma – Revision 1EMA HMPC · 2025
- WHO Monographs on Selected Medicinal Plants (Volumes 1–4)World Health Organization · 2009
- Herbs at a Glance: Evidence-Based Fact Sheets on Botanical ProductsNIH NCCIH · 2024
Related herbs
Black Seed
B Limited clinical evidenceNigella sativa
A spice seed for which small studies saw modest falls in blood sugar, cholesterol and blood pressure. Kitchen amounts are safe.
Valerian Root
A Strong clinical evidenceValeriana officinalis
Dry extracts of valerian root may help with mild nervous tension and sleep problems; they work gradually, so use them for 2–4 weeks.
Chamomile
T Traditional useMatricaria recutita
A gentle herbal tea traditionally used for bloating and mild stomach cramps, common cold symptoms and mouth or throat irritation.
Senna
A Strong clinical evidenceSenna alexandrina
A stimulant laxative for short-term relief of occasional constipation. No longer than 1 week; not for children under 12, in pregnancy or while breastfeeding.
Ginger
A Strong clinical evidenceZingiber officinale
Powdered ginger root taken before travel may help prevent motion-sickness nausea; it is also traditionally used for mild indigestion.