Ashwagandha: what do studies say about effectiveness, safety and interactions?

Ashwagandha (Withania somnifera) has been used in Ayurvedic and Unani traditions. Current products mainly contain root extracts, sometimes extracts of both root and leaf. Available studies suggest possible effects on selected measures of stress, anxiety or sleep, but extracts, doses, durations and populations differ; the evidence does not support a conclusion of general effectiveness. [1][2]

The WHO describes Withania somnifera in the context of medicinal plants; this is not modern clinical evidence for a specific indication. [4] The EMA states that an EU traditional-use monograph for the root could not be established at that stage of its assessment. [3] “Traditionally used” describes historical use; it does not mean “proven effective” or “suitable for everyone.”

Human trials have mainly examined stress, anxiety, fatigue and sleep. The NIH reports favourable signals in several studies while highlighting the diversity of extracts and the need for further research. [2]

A six-week trial in adults with non-restorative sleep observed improvements in several parameters, but one extract and one trial cannot be generalised. [8] In a 12-week trial in middle-aged or older adults who were overweight or mildly obese, perceived stress was not reduced more than with placebo; a secondary fatigue outcome was favourable. [9]

Reported adverse effects include digestive problems, nausea, loose stools and drowsiness; their frequency and severity vary by product and person. [1][2] In an eight-week trial of 80 healthy adults, no adverse events were reported; this does not demonstrate long-term safety or safety in higher-risk populations. [7]

Composition varies according to the species, plant part used, extraction and standardisation. Two products sold under the same name are therefore not necessarily comparable.

The NCCIH reports possible interactions with sedatives, thyroid medicines, immunosuppressants, some diabetes or blood-pressure medicines and anticonvulsants; medical or pharmacy advice is indicated before combining them. [1]

The NCCIH recommends avoiding ashwagandha during pregnancy and breastfeeding; it also advises against its use with thyroid or autoimmune disorders and before surgery, unless appropriate medical advice has been obtained. [1] Children, people with chronic disease or impaired liver or kidney function, and people taking several medicines should not self-medicate.

“Supports stress” does not mean that an effect is guaranteed. A dose studied for one extract cannot automatically be transferred to a root powder. One standardised extract is comparable with another only when the preparation and markers are described. A short study does not validate continuous use for months.

Ashwagandha has been studied, but results depend on the extracts and are often limited by trial duration or size. A small sleep signal does not justify a general promise. Pregnancy, breastfeeding, thyroid or autoimmune disorders, surgery and regular medicines call for professional advice.

1. 01NCCIH, 2024 — https://www.nccih.nih.gov/health/ashwagandha
2. 02NIH Office of Dietary Supplements, 2025 — https://ods.od.nih.gov/factsheets/Ashwagandha-HealthProfessional?print=1
3. 03EMA/HMPC, 2013 — https://www.ema.europa.eu/en/documents/public-statement/final-public-statement-withania-somnifera-l-dunal-radix-first-version_en.pdf
4. 04World Health Organization, 2009 — https://iris.who.int/server/api/core/bitstreams/64ddcde7-127f-455d-827e-3ba757a4fabd/content
5. 05Cochrane Central Register of Controlled Trials, 2026 — https://cochranelibrary.com/central/doi/10.1002/central/CN-02984192/full
6. 06Cheah et al., PLoS One / PubMed, 2021 — https://pubmed.ncbi.nlm.nih.gov/34559859
7. 07Verma et al., Complementary Therapies in Medicine / PubMed, 2021 — https://pubmed.ncbi.nlm.nih.gov/33338583
8. 08Deshpande et al., Sleep Medicine / PubMed, 2020 — https://pubmed.ncbi.nlm.nih.gov/32540634
9. 09Smith et al., Journal of Psychopharmacology / PubMed Central, 2023 — https://pmc.ncbi.nlm.nih.gov/articles/PMC10647917