Ashwagandha: which benefits are proven? Limits and precautions

The benefits of ashwagandha have become a ubiquitous selling point: stress, cortisol, sleep, sport and fertility. Yet this Ayurvedic plant, Withania somnifera, has two sides. It has more clinical trials than most herbs, but the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) recommends that several groups avoid it. Here is what studies actually measure, their limitations and the precautions to know before taking it.

What is ashwagandha?

Ashwagandha (Withania somnifera) is a shrub in the nightshade family, used for centuries in Ayurvedic medicine. It is sometimes called Indian ginseng, although it is not botanically related to ginseng. Its roots are mainly used in food supplements, as powder or extracts.

Its main compounds are steroidal lactones called withanolides, and alkaloids. Their concentrations vary widely depending on the plant part and extract, making study comparisons difficult. ANSES also notes supplements supposedly containing root that have been adulterated with leaves, which are richer in alkaloids.

Which benefits of ashwagandha have studies measured?

No health claim is authorised for ashwagandha in the European Union. The results below therefore describe studies, their doses and populations, rather than effects a product could claim.

Perceived stress and cortisol

This is the most-studied area. A 2022 meta-analysis pooled 12 randomised trials with 1,002 participants aged 25 to 48: ashwagandha reduced perceived stress and anxiety more than placebo. However, results varied greatly between trials, and the authors rate the certainty of the evidence as low.

Two trials illustrate these findings. In 64 stressed adults, 300mg of root extract twice daily for 60 days reduced the perceived stress score by 44%, compared with 5.5% under placebo, and blood cortisol by 27.9%, compared with 7.9%. In 60 adults, 240mg of extract daily for 60 days reduced clinician-rated anxiety and morning cortisol, but not significantly the self-rated stress score. This second trial was funded by the extract manufacturer.

Sleep

A meta-analysis of five trials involving 400 participants found a small but significant effect on overall sleep quality. It was clearer in people with insomnia, at doses of at least 600mg daily and after at least eight weeks. The authors highlight the lack of long-term safety data. To put these findings in context, see our article on sleep and melatonin.

Physical performance

A 2021 Bayesian meta-analysis of 12 studies in healthy adults concluded that ashwagandha had an advantage over placebo for strength, cardiorespiratory capacity and recovery. Trials remain small, and the authors call for more comparable studies, particularly in trained athletes.

Male fertility

In a pilot study, 46 men with oligospermia (fewer than 20 million sperm per millilitre) received 675mg of extract daily or placebo for 90 days. Sperm count increased by 167% in the ashwagandha group, with higher volume and motility. This is a research topic: one small trial cannot establish a conclusion, and infertility requires medical assessment.

Thyroid

In 50 adults with subclinical hypothyroidism (TSH between 4.5 and 10 mIU/l), 600mg of extract daily for eight weeks lowered TSH and increased T3 and T4 hormones compared with placebo. This hormonal effect is also a concern: cases of thyrotoxicosis (excess thyroid hormones) have been reported. Our article on iodine and thyroid function explains the basics.

Why are these results still uncertain?

• Small samples, short durations: the trials cited include 46 to 64 people followed for 8 to 13 weeks.
• Extracts are not comparable: plant part, solvent, withanolide content… ANSES notes that studies rarely specify extract composition.
• Industry funding: some trials are funded by the producer of the extract tested.

These limitations do not invalidate the findings, but they prevent applying a figure from one study to any product sold as ashwagandha.

Is ashwagandha harmful to the liver?

Liver injury is rare but documented. The US National Institutes of Health's LiverTox database states that ashwagandha has not been associated with elevated liver enzymes during use, but has been implicated in cases of clinically apparent liver injury. A series of five cases in Iceland and the United States describes jaundice developing 2 to 12 weeks after starting use, with prolonged itching; tests returned to normal within 1 to 5 months in four patients.

An Indian case series published in 2023 is more concerning. Of eight patients who took a product containing only ashwagandha, five had pre-existing liver disease; three developed acute-on-chronic liver failure and died. Jaundice, dark urine or unusual itching require stopping use and seeking medical advice.

Who should avoid ashwagandha?

In its opinion of 19 April 2024, ANSES recommends avoiding supplements containing ashwagandha in cases of thyroid, liver or heart disease, hyperandrogenism, pregnancy, or treatment with sedatives or central nervous system depressants. As a precaution, it also advises against them during breastfeeding and under age 18. Because drowsiness has been observed in trials, it advises against the plant when driving.

The German Federal Institute for Risk Assessment (BfR) issued similar recommendations in September 2024 for children, pregnant or breastfeeding women and people with liver disease. The US National Institutes of Health also advises against it in cases of autoimmune disease, hormone-sensitive prostate cancer or planned surgery.

What interactions are possible with medicines?

Official sources report possible interactions with:

• sedatives, such as benzodiazepines and sleeping tablets;
• thyroid hormones, such as levothyroxine;
• immunosuppressants;
• medicines for diabetes and high blood pressure;
• antiepileptic medicines.

Is ashwagandha banned in France or Europe?

Not in France at the time of writing (October 2026): in 2024, ANSES issued the cautionary recommendations outlined above without banning sales. Denmark, however, banned it in food supplements in 2023 following a risk assessment performed in 2020, and Germany recommends not using it. Lists of authorised plants are not harmonised across Europe, which ANSES highlights in calling for harmonisation.

Frequently asked questions

How long does ashwagandha take to work?

The cited trials assessed results after 8 to 13 weeks, and the sleep effect was clearer beyond eight weeks. These studies do not show an established effect within a few days.

Should it be taken in the morning or evening?

The cited trials did not compare times of intake: they used one to three doses a day. Because the plant can cause drowsiness, you should not drive if this occurs. Daytime drowsiness is a reason to stop and discuss it with a professional.

Can it be taken continuously?

Tolerability data mainly cover use for no more than three months. According to the US National Institutes of Health's Office of Dietary Supplements, long-term safety is unknown. Prolonged use therefore warrants medical advice, particularly when taking medication.

Can ashwagandha dull emotions?

Online accounts describe a feeling of flattened emotions. This experience was not measured in the trials cited here, which can neither confirm nor rule it out. Any unusual mood change is a reason to stop and discuss it with a doctor.

Root powder or extract: what is the difference?

Trials used standardised extracts at doses of a few hundred milligrams. Unconcentrated root powder does not supply the same amounts of compounds, and the doses cannot be transferred directly. To understand the formats, see our article on capsules, softgels and tablets.

Does ashwagandha increase testosterone?

Evidence is limited. In the 2019 trial in 60 adults, testosterone increased in men over the course of the study without a significant difference from placebo. This possible effect is why the plant is discouraged in cases of hormone-sensitive prostate cancer.

Conclusion

The best-documented benefits of ashwagandha concern perceived stress and, to a lesser extent, sleep: measurable effects from small, short and heterogeneous trials. Against this, safety signals are serious, especially for the liver and thyroid, and French and German authorities urge caution for many groups. The plant therefore warrants individual discussion, ideally with a healthcare professional. Other studied approaches are presented in our article on stress and the ingredients studied in this area. Passionflower, which is less studied, has traditional use recognised in Europe as a herbal medicine, with no authorised health claim for food supplements.

Sources

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6. Ambiye VR et al. (2013). Clinical Evaluation of the Spermatogenic Activity of the Root Extract of Ashwagandha (Withania somnifera) in Oligospermic Males: A Pilot Study. Evidence-Based Complementary and Alternative Medicine, 2013, 571420. doi:10.1155/2013/571420
7. Sharma AK, Basu I, Singh S (2018). Efficacy and Safety of Ashwagandha Root Extract in Subclinical Hypothyroid Patients: A Double-Blind, Randomized Placebo-Controlled Trial. Journal of Alternative and Complementary Medicine, 24(3), 243-248. doi:10.1089/acm.2017.0183
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Food supplements do not replace a varied, balanced diet or a healthy lifestyle. Ask a healthcare professional for advice if you take medication, are pregnant or are breastfeeding.