Ashwagandha Under the Microscope: What Science Really Says About Stress, Sleep, and Cognition

Ashwagandha ( Withania somnifera ) has long been at the top of the dietary supplement market as a “plant anti-stress.” But where does the marketing end and the evidence begin? In a recent review in Nutrients, Polish researchers went through the clinical and mechanistic data and collected everything we know to date: where the signals of benefit are (stress, anxiety, sleep quality, cognitive function), what doses have been studied most often, and what serious questions remain unanswered - from standardization of extracts to long-term safety.

The focus is on withanolides (steroidal lactones) and other active components of the plant. They are associated with antioxidant, anti-inflammatory and neuromodulatory effects and, most importantly, with an effect on the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic system - the biological basis of the "adaptogenic" effect. This is why ashwagandha is considered as a potential support for chronic stress, anxiety, depressive symptoms and sleep disorders.

Background of the study

Ashwagandha ( Withania somnifera ) came to clinical research from Ayurveda as an “adaptogen” – a remedy designed to gently increase stress resistance and normalize body functions without pronounced toxicity. There is biological plausibility to this idea: extracts of the plant contain withanolides and related steroidal lactones, which are credited with antioxidant and anti-inflammatory effects, and most importantly, an effect on the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system. Against this background, small randomized trials have appeared over the past 10-15 years in which ashwagandha has shown a moderate reduction in subjective stress and anxiety, improved sleep quality, and hints of improved memory/attention in adults complaining of fatigue and stress. These effects are often accompanied by a moderate decrease in morning cortisol and an improvement in well-being according to questionnaires – that is, biomarkers and sensations “rhyme,” although not always.

However, the field has systemic weaknesses. Most RCTs are short (usually 8-12, less often 16 weeks), the samples are small, and the composition of the preparations is heterogeneous: different parts of the plant (root/leaves), extraction methods and levels of standardization for withanolides are used. This is typical for the dietary supplement market, but scientifically inconvenient: the results are difficult to compare with each other, and predicting the effect of a specific brand is even more difficult. There are also no uniform "working" doses, although 250-600 mg of standardized extract per day are most often used. Another methodological problem is the reliance on subjective outcomes (stress, sleep, well-being questionnaires) with a limited set of objective metrics (actigraphy, heart rate variability, cognitive batteries), which increases the risk of overestimation of the effect and publication bias.

Short-term safety appears generally acceptable (mostly mild gastrointestinal symptoms and drowsiness), but there is little data for long-term use. Special attention should be paid to vulnerable groups: pregnant and lactating women (lack of evidence), patients on polypharmacy (potential pharmacokinetic interactions), people with autoimmune and endocrine diseases (there are reports of effects on thyroid hormones), as well as rare descriptions of drug-induced liver damage. Therefore, a rational approach is to consider ashwagandha as a possible addition to proven strategies (sleep hygiene, cognitive-behavioral techniques, physical activity, pharmacotherapy if necessary), rather than as a replacement, choosing standardized extracts and monitoring tolerability.

It is these gaps – in drug standardization, study length and size, objective outcomes, and patient stratification – that current reviews seek to fill: they systematize the available signals of benefits for stress, sleep, and cognition, while emphasizing the need for larger, more multicenter, and more rigorously designed trials to understand for whom, at what doses, and for how long ashwagandha really works.

What exactly did the authors watch?

• We analyzed in vivo studies in humans from 2009-2025, including RCTs on stress, anxiety, depression, sleep, and cognition; additionally, the mechanisms of action on the HPA axis and neuroimmune circuits.
• We compared dosages and forms: from root/leaf powder to extracts (including extended-release capsules); we noted a typical range of ~250-600 mg/day of standardized extract.
• We separately examined the bottlenecks: small samples, short duration (usually 4-16 weeks), lack of uniform standards for withanolides and variable quality of supplements on the market.

In summary, the researchers see converging signals of benefit - but with caveats that are important for practitioners and regulators.

What did they find?

• Stress and anxiety. In several RCTs, ashwagandha reduced PSS/HAM-A scores and morning cortisol; a meta-analysis of 558 participants confirmed superiority over placebo for moderate adverse events. Some studies have shown an increase in free testosterone in men.
• Sleep: A series of trials have shown improvements in sleep quality and daytime fatigue with standardized extracts (usually 8-12 weeks).
• Cognitive functions. There are signals for memory and attention, especially in people with subjective complaints; however, many RCTs are small and short, and the authors explicitly ask not to overestimate the size of the effect.
• Safety: No serious AEs were observed in short-term studies; mild GI symptoms/drowsiness were the most common. The main concern is long-term safety and vulnerable groups.

What does "standardization" have to do with it and why is it important? Most products with ashwagandha are released as dietary supplements, simplifying registration - hence the variation in composition/dose and instability of withanolides concentration. The authors insist: without uniform analytical methods and standards for marker molecules, it is difficult to compare the results of RCTs with each other, and it is even more difficult to predict the effect.

How it might work (mechanisms, in short)

• HPA axis shift: moderate reduction in cortisol reactivity to stress.
• Neuromodulation: Potential effects on GABAergic/serotonergic pathways (preclinical data) which resonates with sleep/anxiety improvements.
• Anti-inflammatory and antioxidant circuit: effects on NF-κB and cytokine profile, indirectly supporting cognitive function.

What this does not mean: that ashwagandha is a "natural analogue" of antidepressants or sleeping pills. The authors emphasize that almost all comparisons are with placebo, so the conclusion "no worse than standard pharmacotherapy" cannot be made. Head-to-head RCTs, large samples and long-term observation are needed.

Practical conclusions (with reservations)

• Where to expect benefits: chronic stress, moderate anxiety, mild sleep disorders; possible benefit to attention/memory in case of subjective complaints.
• What doses have been studied most often: ~250-600 mg/day of standardized extract for 8-12 (up to 16) weeks. There is little data beyond that.
• What to look for when choosing: indication of standardization for withanolides, transparent specification of raw materials (root/leaf), form with proven bioavailability.
• Combinations and expectations: Consider as a complement to sleep hygiene, psychoeducation, CBT approaches and, if necessary, pharmacotherapy - not a replacement.

Limitations that the review honestly writes about

• Small and short RCTs → risks of effect overestimation and publication bias.
• Inconsistency of formulas and doses → poor comparability of results.
• Lack of data on “long-term” safety and in vulnerable groups (polypharmacy, endocrine disorders, elderly).
• Quality problems in the dietary supplement market → unstable concentration of active ingredients.

The vector for the future is quite specific: standardize extracts, conduct multicenter long-term RCTs (including vulnerable groups) and include omics/neuroimaging to see who and due to what “works” more. For now, the most sober way to look at ashwagandha is as a tool for supporting well-being with moderate effects and good short-term tolerability with the right choice of form and dose.

Source: Wiciński M. et al. Ashwagandha (Withania somnifera) and Its Effects on Well-Being-A Review. Nutrients. 2025;17(13):2143. https://doi.org/10.3390/nu17132143