Study Limitations & Funding
The common weaknesses in adaptogen trials (small size, short length, varied extracts, risk of bias) and what is and is not known about who pays for the research.
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Short answer. Reviews of adaptogen trials repeatedly describe the same limits: small groups, short studies, many different extracts, and flaws that raise the risk of bias. Who paid for a study matters, and funding is sometimes disclosed in the paper, but we did not find a study that measured whether funding changes adaptogen trial results. So read results as promising or mixed rather than settled, and ask a pharmacist or clinician before using any adaptogen with a medicine.
How the sources define the terms
Risk of bias means features of a study's design or reporting that could push results in one direction. Heterogeneity means trials in a review differ so much in people, preparations or measures that their results do not line up. Conflict of interest means a financial or other tie that could influence how a study is run or reported. For the main study types, see evidence types and study designs.What reviews found about study quality
| Limit | What the source found | Our evidence label |
|---|---|---|
| Small and short | NCCIH says many ashwagandha studies have had small sample sizes. [1] For Asian ginseng, most trials were small (fewer than 200 participants) and shorter than 3 months. [2] A review of 24 ashwagandha and rhodiola trials counted 10 to 590 participants and 3 to 16 weeks. [3] | Limitation |
| Many different preparations | NCCIH notes ashwagandha studies used a variety of preparations. [1] A 2026 review points to heterogeneity in herbal preparations. [4] | Limitation |
| Reporting flaws | The EMA herbal committee (2008) noted deficiencies in describing inclusion and exclusion criteria, the medication, diagnosis, study design and analysis, and that some studies had very few patients. [5] | Limitation |
| Risk of bias in rhodiola trials | In a 2012 systematic review, all 11 included studies had a high or unclear risk of bias. [6] A 2011 review judged most trials of moderate or good quality, but found a lack of independent replications. [7] | Mixed |
| Risk of bias in ashwagandha anxiety trials | A 2014 review found five trials, all with unclear or high risk of bias, and different designs that prevented a meta-analysis. [8] | Limitation |
| Results that disagree | A 2022 meta-analysis of 12 ashwagandha trials found lower anxiety and stress than placebo but rated certainty low and reported very high heterogeneity. [9] | Promising but limited |
These reviews cover different plants and extracts, so a limit found for one does not automatically apply to all. Quality can also differ between trials of the same herb.
Who pays for the research
Funding does not make a study wrong, and it does not make it right. Two examples show that trials differ.- A 2019 randomized trial of an ashwagandha root extract in 60 stressed adults was funded by the company that makes the extract and supplied it. The paper also says the study was independently managed by its principal investigators, who declared no competing interests, and that it was registered in a trial registry. [10]
- A 2012 randomized trial of an ashwagandha root extract in 64 adults lists its source of support as "Nil" and no conflict of interest. [11]
A Cochrane review of 75 included papers on drugs and medical devices (not supplements) found industry-sponsored studies more often reported favorable efficacy results (risk ratio 1.27) and favorable conclusions (1.34) than studies with other sponsors, and said the pattern could not be explained by standard risk-of-bias checks. [12] That finding is from drug and device research. It shows why funding is worth checking, but it does not tell us how large the effect is in supplement trials.
Proper evidence not found: whether sponsorship changes results in adaptogen trials specifically. We searched PubMed for "adaptogen" with conflict of interest, industry funded or sponsor in the title or abstract on 2026-10-23 and found no records, and the adaptogen reviews we read did not analyze it. A title and abstract search can miss papers that discuss funding in the full text.
How to read a trial report
- Which plant part and extract, and was the amount stated?
- How many people, and for how long?
- Was there a placebo comparison, and were the outcomes measured by questionnaire, clinician or lab? See how stress, fatigue and sleep are measured.
- Was the study registered, and are funding and conflicts disclosed? See registered trials and protocols.
- Has anyone independent repeated it?
Frequently asked questions
Are adaptogen studies unreliable?
Reviews describe real limits, including small size, short duration and risk of bias, but also some promising results. The honest summary is "limited", not "useless". [4][9]
Does industry funding mean a result is wrong?
No. Disclosed funding is a reason to look more closely. The Cochrane review found industry-sponsored drug and device studies more often favorable, which is a pattern across many studies, not a verdict on one trial. [12]
Do independent studies agree with company-funded ones?
Proper evidence not found for adaptogens specifically in the sources we read; one review noted a lack of independent replications of rhodiola trials. [7]
Why are there so few long studies?
The sources we read describe the short length but do not explain why. A 2019 trial report said no earlier ashwagandha stress or anxiety study it reviewed ran longer than 8 weeks, [10] and a 2026 review of 24 trials found durations of 3 to 16 weeks. [3]
Where can I check a trial's funding?
Look at the funding, acknowledgments and conflict-of-interest statements at the end of a paper, as in the examples above, and ask a librarian or clinician to help interpret it.
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.
Safety implications
References
- National Center for Complementary and Integrative Health (NIH). Ashwagandha: Usefulness and Safety. Last updated March 2023. Read 2026-10-23.
- National Center for Complementary and Integrative Health (NIH). Asian Ginseng: Usefulness and Safety. Page read 2026-10-23. Read 2026-10-23.
- Łuszczak J, Kocki J. Clinical evidence for the adaptogenic effects of Withania somnifera and Rhodiola rosea: a systematic review with molecular interpretation of psychometric outcomes. Ann Agric Environ Med. 2026. PubMed 41906501. Read 2026-10-23.
- Rao YC, Kumari KM, Kateel R, Mohanbabu Vittalrao A. Phyto adaptogens in stress management and health optimization: current understanding and future perspectives. Complement Med Res. 2026. PubMed 42721096. 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.
- Ishaque S, Shamseer L, Bukutu C, Vohra S. Rhodiola rosea for physical and mental fatigue: a systematic review. BMC Complement Altern Med. 2012. PubMed 22643043. Read 2026-10-23.
- Hung SK, Perry R, Ernst E. The effectiveness and efficacy of Rhodiola rosea L.: a systematic review of randomized clinical trials. Phytomedicine. 2011. PubMed 21036578. Read 2026-10-23.
- Pratte MA, Nanavati KB, Young V, Morley CP. An alternative treatment for anxiety: a systematic review of human trial results reported for the Ayurvedic herb ashwagandha (Withania somnifera). J Altern Complement Med. 2014. PubMed 25405876. Read 2026-10-23.
- Akhgarjand C, Asoudeh F, Bagheri A, et al. Does ashwagandha supplementation have a beneficial effect on the management of anxiety and stress? A systematic review and meta-analysis of randomized controlled trials. Phytother Res. 2022. PubMed 36017529. Read 2026-10-23.
- Lopresti AL, Smith SJ, Malvi H, Kodgule R. An investigation into the stress-relieving and pharmacological actions of an ashwagandha (Withania somnifera) extract: a randomized, double-blind, placebo-controlled study. Medicine (Baltimore). 2019. PubMed 31517876, full text at PMC6750292. Read 2026-10-23.
- Chandrasekhar K, Kapoor J, Anishetty S. A prospective, randomized double-blind, placebo-controlled study of safety and efficacy of a high-concentration full-spectrum extract of ashwagandha root in reducing stress and anxiety in adults. Indian J Psychol Med. 2012. PubMed 23439798, full text at PMC3573577. Read 2026-10-23.
- Lundh A, Lexchin J, Mintzes B, Schroll JB, Bero L. Industry sponsorship and research outcome. Cochrane Database Syst Rev. 2017. PubMed 28207928. Read 2026-10-23.