Human Clinical Studies on Adaptogens: What Exists, Limits and Conflicts of Interest
What human trials of adaptogens exist, how big and how long they are, why reviews disagree, what trials miss about safety, and how to check funding and conflicts of interest.
Content last updated . This page has not been medically reviewed.
Safety first. Natural products can cause side effects and interact with medicines. Read who should be careful, by situation before you use anything on this page.
Information only. This page describes the quality of human research. It does not say any adaptogen treats a condition. Some adaptogen herbs have documented cautions with medicines, pregnancy, surgery, the thyroid and the liver, so ask a pharmacist or clinician first. See how medicine interactions work.
Quick answer
Yes, human trials exist for several adaptogen herbs, but the sources we read describe many of them as small, short, and run with different extracts. [1][2] That is why even careful reviews reach cautious or conflicting conclusions. Evidence label: promising but limited for a few preparations; insufficient evidence for most.
What exists
These are examples from systematic reviews and NIH summaries. A "study" here is a human trial or a pooled review of trials. The counts show volume, not quality.| Herb (scientific name) | What a review or NIH summary found | Strength and limits |
|---|---|---|
| Ashwagandha (Withania somnifera) | A 2022 meta-analysis pooled 12 papers (1,002 people) and found lower anxiety and stress scores than placebo; certainty of evidence was low and results varied widely between trials (heterogeneity I2 about 94% for anxiety). [3] A 2026 meta-analysis included 22 trials and called for high-quality trials to address heterogeneity. [4] NCCIH: some preparations may be effective for insomnia and stress, unclear for anxiety. [2] | Promising but limited; preparation (root, leaf, extract) varied; adults mostly 25 to 48 in the 2022 pool |
| Rhodiola (Rhodiola rosea) | A 2011 review found 11 placebo-controlled randomized trials. [5] A 2012 review of the herb for fatigue found 11 studies and rated all as high risk of bias or having reporting flaws. [6] NCCIH: not enough reliable evidence for any purpose. [7] | Mixed to insufficient; reviews disagree on quality |
| Ginseng (Panax ginseng, Panax quinquefolius) | A 2018 review of 10 studies of ginseng for fatigue found modest evidence for efficacy and a low risk of adverse events, and called for methodologically stronger research. [8] NCCIH says most Asian ginseng trials have fewer than 200 participants and last under 3 months. [9] | Promising but limited; mostly small and short |
| Eleuthero (Eleutherococcus senticosus) | A 2008 European committee paper said none of the studies it reviewed would be sufficient to substantiate efficacy in a clearly defined clinical condition. [10] | Insufficient evidence; paper is from 2008, newer trials were not reviewed here |
For the rest, see research by ingredient.
Limits that apply across many trials
- Small samples and short durations. A 2026 review says many randomized trials of adaptogens have relatively small sample sizes and short intervention periods. [1]
- Different products. The same review cites heterogeneity in extract composition and standardization and in dosing protocols. [1] NCCIH notes ashwagandha studies used a variety of preparations. [2]
- Reporting flaws. The EMA paper listed shortcomings in the description of inclusion and exclusion criteria, and in some studies a very small number of patients. [10]
- Lack of independent replication. A 2011 review of rhodiola said single studies lacked independent replications. [5]
- Biomarkers vs how people feel. Only a limited number of studies measure molecular biomarkers together with clinical outcomes. [1]
- Two reviews can disagree because they ask different questions and use different quality tools. For rhodiola, one review judged most trials moderate or good while another found all high risk of bias. [5][6]
How to read a trial result
- Who and how many? Count participants, ages and health status.
- Which product? Species, plant part, extract and standardization, as the trial reported it.
- How long? Weeks versus months.
- What was measured? Symptom questionnaires or lab markers; see how stress, fatigue and sleep are measured.
- Compared with what? A placebo-controlled randomized design is stronger than an uncontrolled one; see evidence types and study designs.
- Was it repeated by others?
Frequently asked questions
How many human studies of adaptogens exist?
It depends on the plant. For example, one meta-analysis pooled 12 ashwagandha trials with 1,002 participants and another pooled 22 trials, while a rhodiola review found 11 randomized trials. [3][4][5] Counts are not quality.
Are the trials good quality?
Reviews describe many as small and short, with different extracts. [1] Quality judgments differ between reviews even for the same herb. [5][6]
Do trials show adaptogens are safe?
Not fully. NCCIH says long-term safety of ashwagandha is not established and describes rare liver injury cases. [2] A review of adverse event reports advised monitoring when adaptogens are used with antidepressants. [11]
Who funds adaptogen trials?
It varies and we did not find a pooled analysis. Check each paper's funding and conflict-of-interest statements; one 2024 trial's statement discloses a study sponsor. [12]
What should I do with this information?
Use it to read claims critically. Ask a pharmacist or clinician about your situation; do not start, stop or change a prescribed medicine on the basis of a headline. See limitations and funding for more on study design issues.
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.
What trials may miss about safety
Short trials in healthy volunteers are not designed to catch rare or long-term harms or interactions.
- NCCIH says there is not enough information to reach conclusions about ashwagandha's long-term safety. [2] It also says that although rare, there have been a number of cases linking liver injury to ashwagandha supplements. [2]
- A 2023 retrospective review evaluated 1,816 adverse event reports and identified 30 in which, by the authors' analysis, side effects had a causal relationship with antidepressants taken together with adaptogen herbs. [11] It is a record of reports, not a trial, and cannot give rates, but the authors advised clinicians to monitor. [11]
- NCCIH says ashwagandha might interact with some medications, including those for diabetes and high blood pressure. [2]
- A 2018 review of ginseng for fatigue found a low risk of adverse events in the 10 studies it reviewed. [8] That is not proof of safety for every product or person.
Funding and conflicts of interest
Funding and ties matter because a company can design, run or pay for a trial of its own product. Rather than guess, here is what we found.
- Proper evidence not found in the sources we read for a systematic analysis of how funding or conflicts of interest relate to results in adaptogen trials. We searched PubMed for reviews of funding and conflicts of interest in ashwagandha and adaptogen trials, and found individual trial records but not such an analysis.
- Trial papers carry a conflict-of-interest statement. As one example, a 2024 ashwagandha trial states that its principal investigator has no financial or intellectual property conflict with the study sponsor or the nutrient examined, which tells a reader a sponsor existed and that the paper discloses how its authors relate to it. [12] That is an example of where to look, not a judgment of that trial.
- In the NIH pages and review abstracts we read, no comparison of funded and unfunded trials was reported.
Where to look in any paper: the funding statement, the conflict-of-interest statement, whether the extract was supplied by the maker, and whether an independent group repeated the result.
Safety and who to ask
If you are on any prescription, especially antidepressants, ask the prescriber or pharmacist before adding an adaptogen. [11] Tell your surgical team, because NCCIH says ashwagandha is not recommended before surgery or for people with autoimmune or thyroid disorders. [2] If you have symptoms you think may be linked to a supplement, contact a clinician or pharmacist, and see liver safety and supplements. Product quality varies; see quality testing and certifications. If you are in distress or thinking about harming yourself, call or text 988 (US).
References
- Nutrients 2026. System-Level, Molecular and Cellular Mechanisms of Selected Plant Adaptogens - A Review. Review, full text read 2026-10-23.
- National Center for Complementary and Integrative Health (NIH). Ashwagandha: Usefulness and Safety. Read 2026-10-23.
- Phytother Res 2022. Does Ashwagandha supplementation have a beneficial effect on the management of anxiety and stress? A systematic review and meta-analysis of randomized controlled trials. Abstract read 2026-10-23.
- Complement Ther Med 2026. Effects of ashwagandha (Withania somnifera) on mental health in adults: a systematic review and dose-response meta-analysis of randomized controlled trials. Abstract read 2026-10-23.
- Phytomedicine 2011. The effectiveness and efficacy of Rhodiola rosea L.: a systematic review of randomized clinical trials. Systematic review, abstract read 2026-10-23.
- BMC Complement Altern Med 2012. Rhodiola rosea for physical and mental fatigue: a systematic review. Systematic review, abstract read 2026-10-23.
- National Center for Complementary and Integrative Health (NIH). Rhodiola: Usefulness and Safety. Read 2026-10-23.
- J Altern Complement Med 2018. Ginseng as a Treatment for Fatigue: A Systematic Review. Systematic review, abstract read 2026-10-23.
- National Center for Complementary and Integrative Health (NIH). Asian Ginseng: Usefulness and Safety. Read 2026-10-23.
- European Medicines Agency, Committee on Herbal Medicinal Products (HMPC). Reflection paper on the adaptogenic concept (EMEA/HMPC/102655/2007), adopted 8 May 2008. Read 2026-10-23.
- Front Pharmacol 2023. Harder, better, faster, stronger? Retrospective chart review of adverse events of interactions between adaptogens and antidepressant drugs. Abstract read 2026-10-23.
- Nutrients 2024. Acute and Repeated Ashwagandha Supplementation Improves Markers of Cognitive Function and Mood. Trial record with conflict-of-interest statement, 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.