What “evidence” means here

Every plant profile and plan step here carries an evidence label. It is not our opinion of whether something works. It reports how the cited source, usually part of the NIH, describes the research behind one specific claim.

The four levels

• Established: the source describes consistent findings from well-designed studies. It is the rarest label here, and it applies to one claim, never to a whole plant.
• Limited: some studies exist, but the source calls them small, mixed or preliminary. Something may be there; the research cannot say so with confidence.
• Insufficient: the source says there is not enough reliable research to know either way. That is not the same as “it does nothing”; nobody has looked carefully enough yet.
• Practice: a habit or technique with a plain rationale, such as washing your face or keeping a regular bedtime. It is not a health-effect claim, so we do not dress it up as one.

When a source is silent, we leave the point out.

How a claim earns its level

NCCIH describes the ladder research climbs. Basic research tests ideas in the lab. Translational research carries those results toward something that can be tried in people. Clinical trials, done with people, give the clearest information about whether an approach is effective and safe in humans. Systematic reviews then gather many studies to check their quality and look for converging evidence; when many studies agree, the result is more likely to be reliable.

Inside a trial, a few design choices carry the weight. An experimental group that receives the approach is compared with a control group that receives standard care or an inactive substance. In a double-blind trial neither participants nor researchers know who is in which group, because knowing colors everyone's impression of whether people improved. Small studies are more likely to produce results due to chance; large ones better reflect the wider population. A result can be statistically significant, meaning unlikely to be chance, and still too small to matter to a patient. A single study rarely provides a final answer.

Nine questions for any headline

NCCIH publishes a checklist for health news stories. We ask the same questions of every study cited here:

1. Was it tested on people, or only in animals or the lab?
2. Are there alternatives to the approach being discussed?
3. Were enough people studied?
4. Were the results big enough to be meaningful to you?
5. Did the story talk about the study's limitations?
6. Were the participants similar to you in age, race or sex?
7. Was the study long enough to show long-term benefits or risks?
8. Is this the first time a study has reported these results?
9. Was it funded by a group that could profit from the findings?

NCCIH adds that a story is more likely to be accurate when it comes from an outlet not promoting a product, is written by a trained health reporter, and quotes experts not connected to the study. Unless you read the original source, it says, it is hard to know whether a story is accurate. Anecdotes are not evidence, and “natural” is not a result: NCCIH notes that major studies found echinacea ineffective for the common cold, and large trials found ginkgo did not help with dementia or cognitive decline. The label on a claim matters more than the reputation of the plant.