Herb Research Gaps: What Is Still Unknown About Medicinal Herbs
Where research on medicinal herbs is thin: short trials, unclear products, safety questions in pregnancy and with medicines, and what to do as a reader.
Content last updated . This page has not been medically reviewed.
Safety first. Natural products can cause side effects and interact with medicines. Read herb safety and interactions before you use anything on this page.
"Not proven" and "proven not to work" are different things. For many herbs, the honest answer to "does it work?" is that the research has not been done well enough, or at all, to say. This page lists the main places where herb research is thin, using what government and journal sources say. It is not advice on whether to take any herb. For the numbers behind how much is published, see our PubMed snapshot.
Where the gaps are
| Gap | What the sources say |
|---|---|
| Trials that stop early | For St. John's wort and depression, NCCIH says it is uncertain whether the benefit holds for severe depression or for periods longer than 12 weeks. [1] |
| Uses with little or no research | For St. John's wort, NCCIH says the evidence for conditions other than depression is insufficient for definite conclusions. [1] For echinacea, it says much less research has been done on uses other than colds. [2] |
| Unclear findings even after many trials | A Cochrane review of 24 echinacea trials (4,631 participants) concluded echinacea has not been shown to help treat colds, and any weak preventive effect may not be clinically meaningful. [3] |
| Long-term safety | NCCIH describes echinacea safety for short periods of use, and says little is known about its use while breastfeeding. [2] |
| Children and pregnancy | NCCIH says many dietary supplements have not been tested in pregnant women, nursing mothers or children. [4] |
| Medicine interactions | For echinacea, NCCIH says there is conflicting evidence about interactions with some drugs processed by the liver. [2] St. John's wort has clearer warnings about interactions. [1] |
| Product identity | NCCIH says an herbal supplement may contain dozens of chemical compounds and all of its ingredients may not be known. [5] |
| Poor reporting | A review of 206 herbal trials found about 45% of reporting checklist items were reported, and common gaps included details of the herbal preparation, such as the percentage of active constituents. [6] |
Why these gaps exist
Few long trials. Herb trials are often short. A trial that ends at 12 weeks cannot tell you about year-two effects or rare harms. [1] Our page on how herb clinical trials are designed explains why length and size matter.
The product is not always the same. The echinacea Cochrane review found trials used preparations based on different species and plant parts. [3] That makes it hard to combine results into one answer. This is covered in why herb studies disagree. NCCIH tells researchers that product information and expertise are required in grant applications, and gives the example that botanists trained in taxonomy may be needed to identify voucher specimens accurately. [7] That is a sign of how important correct plant identity is.
Reports leave out key details. If a trial does not say what exactly was in the capsule, other people cannot repeat it or compare it with a later study. [6]
Safety gets less attention than benefit. Pregnancy, breastfeeding and children are areas where NCCIH says many supplements have not been tested. [4] Older adults and combinations of several products are also reasonable questions to raise with a pharmacist, but the sources we read do not give herb-specific research findings on them, so we do not claim any here.
Traditional use is not a trial. A long history of use tells us what people have tried. It does not tell us whether the herb works or how safe it is. See traditional use versus research evidence.
Narrow outcomes. St. John's wort is a good example: the better-studied use is depression, and for other conditions NCCIH says evidence is insufficient. [1] A herb can be well studied for one question and barely studied for the rest.
What we could not verify. We did not find a source we could read that gives reliable numbers for how often herb trials go unpublished, how many herbs have never had a human trial, or how often herbs are compared head to head with each other. We leave those out rather than guess.
What NCCIH says about research needs
NCCIH says it is committed to rigorous scientific investigation of natural products. It notes many natural products are complex, with multiple molecular constituents that may contribute to their effects. [7] On the public side, it states that not all products from nature have been shown to be effective, and that scientists are studying many of these products to identify what ingredients may be active. [5]
What to do as a reader
- Ask what was actually tested: which species, which part, which extract. [3][6]
- Check how long the study lasted and who was in it. [1][4]
- Treat "no proof" as "unknown", not as "safe". [4][5]
- Tell your doctor and pharmacist about every herb and supplement you use, especially before surgery or alongside medicines. [4]
- Use our guide to reading a herb study or news headline, the evidence and safety table, and the research hub.
Frequently asked questions
Does "not enough research" mean a herb does not work?
No. It means we do not know. For St. John's wort outside depression, NCCIH says the evidence is insufficient for definite conclusions. [1]
Does "natural" mean it has been shown to be safe?
No. NCCIH says natural does not always mean safer or better, and that not all products from nature have been shown to be effective. [5]
Are herbs tested in pregnancy and children?
NCCIH says many dietary supplements have not been tested in pregnant women, nursing mothers or children. [4] Check with a clinician before use.
Why do herb studies leave out details about the product?
We did not find a source explaining why. A review of 206 trials found details such as the percentage of active constituents were commonly missing. [6]
References
- National Center for Complementary and Integrative Health (NCCIH). St. John's Wort. Read 2026-10-24.
- National Center for Complementary and Integrative Health (NCCIH). Echinacea. Read 2026-10-24.
- Karsch-Völk M, et al. Echinacea for preventing and treating the common cold. Cochrane Database Syst Rev. 2014. PMID 24554461. Read 2026-10-24.
- National Center for Complementary and Integrative Health (NCCIH). Using Dietary Supplements Wisely. Read 2026-10-24.
- National Center for Complementary and Integrative Health (NCCIH). Natural Doesn't Necessarily Mean Safer, or Better. Read 2026-10-24.
- Gagnier JJ, et al. Quality of reporting of randomized controlled trials of herbal medicine interventions. Am J Med. 2006. PMID 16945616. Read 2026-10-24.
- National Center for Complementary and Integrative Health (NCCIH). Natural Products Research: Information for Researchers. Read 2026-10-24.