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How Long Different Ingredients Have Been Studied

How long human trials and official monographs have covered ashwagandha, rhodiola, ginseng, eleuthero and astragalus, and why a short study cannot show long-term safety or how fast anything works.

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.

Quick answer
Human studies of adaptogens are mostly short: weeks to a few months. NIH says ashwagandha may be safe in the short term (up to 3 months) and that there is not enough information to reach conclusions about long-term safety. [1] "Not studied for longer" does not mean "safe for longer", and it does not mean "unsafe" either.

"Adaptogen" is a contested term. Each plant has to be judged on its own studies, and a result for one plant does not transfer to another.

How long each plant has been studied

PlantLongest periods we foundWhat the source saysStrength of the long-term evidence
Ashwagandha (Withania somnifera), root and root/leaf extractsTrials of 60 days, 8 weeks and 10 weeks; one 24-week safety trial [2]NIH: possibly safe up to 3 months; long-term safety not established [1]Insufficient evidence beyond 3 months
Rhodiola (Rhodiola rosea), rootTrials of 2 weeks and 28 daysNIH: possibly safe up to 12 weeks [3]Insufficient evidence beyond 12 weeks
Asian ginseng (Panax ginseng), rootMost trials shorter than 3 monthsNIH: short-term oral use up to 6 months appears safe for most people; long-term safety questioned [4]Insufficient evidence
Eleuthero (Eleutherococcus senticosus), rootNot covered in the NIH pages we readEU monograph: not to be taken for more than 2 months [5]Traditional use only
Astragalus, rootStudies up to 4 monthsNIH: 4 months did not seem to cause adverse effects; a thorough safety evaluation has not been done [6]Insufficient evidence

NIH names the astragalus plant as Astragalus membranaceus. GBIF lists Astragalus mongholicus Bunge as a separate accepted name, so check which species a product or study used. [6][7]

Plant names were checked against the GBIF database, which lists each as an accepted name. [8][9][10][11]

What the individual trials covered

  • Ashwagandha, 60 days: two trials in adults with stress gave a root extract, twice daily in one and once daily in the other, for 60 days. [12][13]
  • Ashwagandha, 10 weeks: a placebo-controlled trial in 60 people with insomnia and anxiety lasted 10 weeks. [14]
  • Ashwagandha, 24 weeks: a trial in 1,200 healthy adults after a COVID-19 vaccine reported that safety and tolerability were comparable to placebo, with mild, mostly gut-related side effects. It tested safety, not stress or sleep. [15]
  • Rhodiola: one trial ran two weeks per period in physicians on night duty, another 28 days in adults with stress-related fatigue. [16][17]
  • Asian ginseng: a meta-analysis of 19 trials in fatigue found no significant overall reduction with ginseng versus controls, with small effects in some subgroups. [18]

How long do adaptogens take to work?

Proper evidence not found. We searched PubMed and read NIH summaries, and none of the sources we read tested how soon an effect starts. Trials usually measured results at set points, so they show a difference after weeks, not a start date. In the ashwagandha sleep trial, sleep onset improved in both the ashwagandha and placebo groups, and was significantly shorter with ashwagandha only after 10 weeks. [14] In the rhodiola fatigue trial, people taking placebo also improved. [17] Placebo response can look like a quick effect.

What a short study cannot tell us

  • Long-term safety, including rare problems. NIH notes that liver injury linked to ashwagandha is rare but reported. [1]
  • What happens when a person stops. We did not find a trial built to test this.
  • Whether results hold in older people, children, or people with health conditions, since the trials above enrolled healthy, stressed or specific patient groups.

Frequently asked questions

How long can I take ashwagandha safely?

Nobody can promise a safe length. NIH says up to 3 months may be safe and long-term safety is unknown. [1] Your clinician can weigh this for you.

How long can rhodiola be used?

NIH says possibly safe for up to 12 weeks. [3] The 2024 European monograph tells people to consult a clinician if symptoms last longer than 2 weeks. [19]

Are long-term effects of adaptogens known?

Mostly not. Most Asian ginseng trials were small and shorter than 3 months, and NIH says larger, longer studies are needed. [4]

Does a longer trial mean a stronger result?

No. A longer trial can show more about safety and lasting effects, but quality, size and the extract used still decide how much weight a result deserves. See Study Limitations and Funding.

Where are study amounts listed?

See Study Amounts and Using Adaptogens.

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 and when to ask
Stop and seek advice if a new symptom appears while using any adaptogen. See When to Stop and Seek Advice and Safety. NIH says ashwagandha should be avoided during pregnancy. [1] Ask a pharmacist before combining with medicines; see How Interactions Work.
References
  1. National Center for Complementary and Integrative Health (NIH). Ashwagandha: Usefulness and Safety. Page last updated March 2023. Read 2026-10-23.
  2. Clinical evaluation of the pharmacological impact of ashwagandha root extract on sleep in healthy volunteers and insomnia patients: a double-blind, randomized, parallel-group, placebo-controlled study. J Ethnopharmacol. 2021. PMID 32818573 (abstract read 2026-10-23).
  3. National Center for Complementary and Integrative Health (NIH). Rhodiola: Usefulness and Safety. Page last updated April 2025. Read 2026-10-23.
  4. National Center for Complementary and Integrative Health (NIH). Asian Ginseng: Usefulness and Safety. Page last updated February 2025. Read 2026-10-23.
  5. European Medicines Agency, Committee on Herbal Medicinal Products (HMPC). Community herbal monograph on Eleutherococcus senticosus (Rupr. et Maxim.) Maxim., radix (EMA/HMPC/680618/2013), version of 25 March 2014. Read 2026-10-23.
  6. National Center for Complementary and Integrative Health (NIH). Astragalus: Usefulness and Safety. Page last updated May 2025. Read 2026-10-23.
  7. GBIF Secretariat. Astragalus mongholicus Bunge, GBIF Backbone Taxonomy, accepted name, family Fabaceae. Read 2026-10-23.
  8. GBIF Secretariat. Withania somnifera (L.) Dunal, GBIF Backbone Taxonomy, accepted name, family Solanaceae. Read 2026-10-23.
  9. GBIF Secretariat. Rhodiola rosea L., GBIF Backbone Taxonomy, accepted name, family Crassulaceae. Read 2026-10-23.
  10. GBIF Secretariat. Panax ginseng C.A.Mey., GBIF Backbone Taxonomy, accepted name, family Araliaceae. Read 2026-10-23.
  11. GBIF Secretariat. Eleutherococcus senticosus (Rupr. & Maxim.) Maxim., GBIF Backbone Taxonomy, accepted name, family Araliaceae. Read 2026-10-23.
  12. 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. PMID 23439798 (abstract read 2026-10-23).
  13. Lopresti AL, Smith SJ, Malvi H, Kodgule R. An investigation into the stress-relieving and pharmacological actions of an ashwagandha extract: a randomized, double-blind, placebo-controlled study. Medicine (Baltimore). 2019. PMID 31517876 (abstract read 2026-10-23).
  14. Langade D, Kanchi S, Salve J, Debnath K, Ambegaokar D. Efficacy and safety of ashwagandha (Withania somnifera) root extract in insomnia and anxiety: a double-blind, randomized, placebo-controlled study. Cureus. 2019. PMID 31728244 (abstract read 2026-10-23).
  15. Safe prolonged prophylactic use and tolerability of Ashwagandha following COVID-19 vaccination over 24 weeks: a multicentre randomized double-blind placebo-controlled trial. Front Med (Lausanne). 2026. PMID 42694770 (abstract read 2026-10-23).
  16. Darbinyan V, Kteyan A, Panossian A, et al. Rhodiola rosea in stress induced fatigue: a double blind cross-over study of a standardized extract with a repeated low-dose regimen on the mental performance of healthy physicians during night duty. Phytomedicine. 2000. PMID 11081987 (abstract read 2026-10-23).
  17. Olsson EM, von Scheele B, Panossian AG. A randomised, double-blind, placebo-controlled, parallel-group study of the standardised extract of the roots of Rhodiola rosea in the treatment of subjects with stress-related fatigue. Planta Med. 2009. PMID 19016404 (abstract read 2026-10-23).
  18. Ginseng and ginseng herbal formulas for symptomatic management of fatigue: a systematic review and meta-analysis. J Integr Complement Med. 2023. PMID 36730693 (abstract read 2026-10-23).
  19. European Medicines Agency, Committee on Herbal Medicinal Products (HMPC). European Union herbal monograph on Rhodiola rosea L., rhizoma et radix, Final, Revision 1 (EMA/HMPC/24177/2023), adopted 20 March 2024. 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.