Ashwagandha for Stress and Cortisol: What the Research Actually Says

Ashwagandha is one of the most-discussed herbal supplements in the stress and anxiety space. It has accumulated more clinical trial data than almost any other adaptogen, and the popular coverage of that research is extensive. But popular coverage and what the research actually shows are not always the same thing.

This post examines the evidence honestly including the most recent meta-analyses, the findings that complicate the simple narrative, and what the science genuinely does and does not support. It is a longer read than most supplement blog posts. That is because the evidence deserves more than a bullet-point summary.

Cortisol: What It Is and Why It Matters

Before looking at what ashwagandha research has investigated, it helps to understand what cortisol actually is and why it is used as a research endpoint.

Cortisol is a glucocorticoid hormone produced by the adrenal cortex the outer layer of the adrenal glands, which sit above the kidneys. Its release is controlled by the hypothalamic-pituitary-adrenal (HPA) axis: a three-tier communication system in which the hypothalamus signals the pituitary gland to release adrenocorticotropic hormone (ACTH), which in turn signals the adrenal glands to produce cortisol.

Cortisol's acute function is adaptive. During genuine threat or challenge, cortisol rapidly increases blood glucose availability, suppresses non-emergency processes (including immune function and digestion), and sharpens alertness preparing the body for immediate response. Under normal conditions, elevated cortisol feeds back negatively to the hypothalamus and pituitary, signalling the system to downregulate. This negative feedback loop is the HPA axis's self-regulating mechanism.

The problem emerges under chronic stress. When the HPA axis is repeatedly or continuously activated by sustained psychological pressure, poor sleep, overtraining, or other persistent stressors the negative feedback loop becomes impaired and baseline cortisol output drifts upward over time. Chronically elevated cortisol is associated with disrupted sleep architecture, suppression of immune function, impaired memory and executive function, mood dysregulation, and metabolic changes including increased abdominal fat storage. Research has shown that prolonged cortisol elevation is also associated with hippocampal atrophy structural changes in the brain region critical to memory and emotional regulation.

This is why cortisol level is used as a biological stress marker in clinical research. It is a measurable, objective endpoint that avoids the subjectivity of self-report questionnaires though it comes with its own measurement limitations, discussed below.

The Proposed Mechanism: How Ashwagandha May Influence the HPA Axis

Ashwagandha's primary bioactive compounds the withanolides, a class of steroidal lactones concentrated in the root are proposed to influence the stress response through several overlapping mechanisms:

HPA axis modulation. Research suggests withanolides may interact with glucocorticoid receptors and modulate the HPA axis feedback system, potentially supporting the regulation of cortisol output during periods of sustained stress. The precise receptor-level mechanism is still being characterised.

GABAergic signalling. Ashwagandha constituents appear to influence gamma-aminobutyric acid (GABA) signalling the brain's primary inhibitory neurotransmitter system. GABAergic activity is associated with reduced neuronal excitability and a calmer physiological state. This pathway is also the mechanism by which many anxiolytic medications (including benzodiazepines) operate, though at very different potency levels.

Anti-inflammatory and antioxidant pathways. Withanolides have been shown to inhibit NF-κB (a key inflammatory signalling protein) and activate Nrf2 (a master regulator of antioxidant gene expression). Since chronic stress and elevated cortisol are both associated with increased inflammatory markers, these pathways may contribute to ashwagandha's studied effects.

Neuroprotection. Preclinical research has shown that ashwagandha constituents can support neuronal health and modulate neurotrophic factors relevant to the hippocampal effects of chronic stress, though direct translation from preclinical to human outcomes requires caution.

What the Clinical Research Has Found

The cortisol trials: consistent signal, specific context

Multiple randomised controlled trials have investigated ashwagandha's effect on serum cortisol levels. The most cited foundational study (Chandrasekhar et al., 2012, Indian Journal of Psychological Medicine) randomised 64 adults with chronic stress history to 300mg of KSM-66 ashwagandha or placebo twice daily for 60 days and found a 27.9% reduction in serum cortisol levels in the ashwagandha group compared to placebo alongside significant reductions on validated stress scales (Perceived Stress Scale: 44% reduction; GHQ-28: 72.3%).

A 2023 systematic review in Nutrients (Della Porta et al.) examined studies specifically measuring cortisol levels in stressed human subjects taking ashwagandha and found consistent reductions across trials. A 2025 review in Phytotherapy Research (Brendler, 2025) concluded that multiple studies consistently show ashwagandha-associated reductions in cortisol levels, supporting its proposed anti-stress effects via modulation of HPA axis activity.

The 2025 meta-analysis: an important nuance

The most critical piece of recent evidence for anyone trying to read the science honestly is a 2025 systematic review and meta-analysis by Albalawi, published in Nutrition & Health, which examined seven RCTs measuring cortisol and six measuring perceived stress (Perceived Stress Scale scores) in 488 participants across trials of at least two weeks with oral doses of 250mg or more per day.

The findings are more nuanced than a simple positive story:

• Cortisol: statistically significant reduction found. The pooled analysis found a statistically significant reduction in cortisol levels of −1.16 µg/dL (95% CI: −1.64 to −0.69, P < 0.001) in ashwagandha groups versus placebo.

• Perceived stress (PSS): no significant impact found. Despite the cortisol finding, the meta-analysis found no statistically significant impact on perceived stress as measured by the Perceived Stress Scale (SMD = −0.355, 95% CI: −1.188 to 0.47; P = 0.40).

The authors' commentary on this disconnect is worth understanding. They recommended longer treatment duration and broader demographic inclusion in future trials, and noted that the gap between an objective biomarker (cortisol) and a subjective self-report measure (PSS) may reflect the complexity of stress as a multidimensional experience that a single biomarker cannot fully represent.

This finding does not mean ashwagandha is ineffective. It means the relationship between cortisol reduction and subjective stress experience is not straightforward, and that the evidence — while genuinely significant on cortisol as a measured endpoint does not yet cleanly translate to an equally robust signal on how people feel.

The broader 2025 meta-analysis (Bachour et al.)

A separate systematic review and meta-analysis published in BJPsych Open in June 2025 (Bachour et al.) covered 15 RCTs with a combined 873 participants and found that ashwagandha supplementation significantly reduced anxiety compared to placebo as measured by the Hamilton Anxiety Rating Scale (HAM-A), alongside reductions in cortisol. This is one of the larger and more recently published meta-analyses in this area, and its findings align broadly with the growing body of evidence while the individual trial heterogeneity (different extracts, doses, durations, populations) remains a consistent limitation across the literature.

The 2024 meta-analysis (Arumugam et al., ScienceDirect)

A comprehensive meta-analysis published in 2024 in the Journal of Ethnopharmacology found statistically significant improvements in overall stress and anxiety and a notable reduction in serum cortisol levels pooled across included trials. The authors concluded the evidence is "promising" while noting the limitations: most trials are short (6–12 weeks), conducted predominantly in Indian populations, and use a range of different ashwagandha extracts with varying withanolide content making direct comparison across studies imperfect.

Interpreting Cortisol Measurements: Limitations Worth Understanding

Serum cortisol is a useful research endpoint, but it has limitations that matter for interpreting ashwagandha trials:

Diurnal variation. Cortisol follows a predictable daily rhythm peaking shortly after waking (the cortisol awakening response) and declining through the day to its lowest point at night. Single blood draws at inconsistent times can introduce significant variability. Well-designed trials control for this with standardised morning sampling or 24-hour urinary cortisol, but not all studies in the ashwagandha literature do this consistently.

Acute vs chronic measures. A single serum sample captures a momentary snapshot of cortisol, not an average or baseline. Hair cortisol analysis which integrates cortisol output over weeks or months is a more reliable chronic stress marker but is less commonly used in supplement trials.

Cortisol as a proxy for stress experience. As the Albalawi meta-analysis demonstrated, a reduction in measured serum cortisol does not automatically translate into a proportional reduction in how stressed a person feels. Stress is a complex biopsychosocial experience involving cognitive appraisal, social context, coping resources, and neurological factors that a single hormone measurement cannot fully capture.

Population specificity. Most published ashwagandha trials including the majority of KSM-66 trials have been conducted with participants in India who reported high baseline stress. Whether findings generalise equivalently to the UK adult population experiencing typical everyday stress, rather than clinically elevated stress levels, requires further investigation.

A New Safety Note: HPA Suppression With Chronic High-Dose Use

A 2026 case report published in Endocrinology, Diabetes & Metabolism Case Reports (Brendler et al.) described a case of adrenal hypofunction where the adrenal glands produce insufficient cortisol in a patient with chronic, high-dose ashwagandha use. A review of existing literature found only two documented case reports of adrenal hypofunction secondary to ashwagandha (2022 and 2024 and 2026), making this rare, but the authors noted that the long-term endocrine consequences of chronic high-dose consumption remain incompletely characterised.

The implication: while ashwagandha's cortisol-moderating effects are the basis of its research interest, the same HPA modulation that produces that effect could in some individuals at high doses over extended periods result in excess cortisol suppression. This is not a reason to avoid ashwagandha at standard doses, but it is a reason why:

1. Standard supplement doses (300–600mg per day of a standardised root extract) matter

2. Chronic use at significantly higher doses warrants medical supervision

3. People with adrenal or cortisol-related conditions should consult their GP

What the Evidence Does and Does Not Support

To be precise:

Reasonably supported by the current evidence (multiple RCTs and meta-analyses):

• Ashwagandha supplementation is associated with statistically significant reductions in serum cortisol in stressed adults over 6–12 weeks

• Ashwagandha supplementation is associated with reductions in anxiety measures (HAM-A) across multiple trials

• Improvements in validated stress scale scores (PSS, GHQ-28, DASS) have been observed in multiple individual trials

Where the evidence is less consistent or needs further development:

• The translation from cortisol biomarker reduction to subjective perceived stress improvement is not robustly established (Albalawi 2025 meta-analysis)

• Most evidence comes from short-duration trials (6–12 weeks) in Indian populations with high baseline stress

• Different extracts, doses, and populations make pooled conclusions imperfect

Not supported by EFSA-authorised claims:

• No health claims for ashwagandha are authorised in the UK or EU — they remain on the EFSA "on-hold" list. No claims can be made on supplement labels or in product marketing regardless of the research findings above

Where KSM-66 Fits in This Picture

Across the trials cited in major meta-analyses, KSM-66 is the most consistently represented standardised extract. Its root-only extraction and standardisation to 5% withanolides means the dose of bioactive compounds is defined and reproducible across studies. This makes it the most clinically interpretable form when a trial uses KSM-66 at 300mg twice daily, you know what withanolide concentration was delivered. Generic ashwagandha products cannot make the same claim.

Nyra Nutrition's KSM-66 Ashwagandha uses the KSM-66 extract at the standardised 5% withanolide concentration from root only. If you are considering ashwagandha based on the research described in this post, read the label and consult a healthcare professional if you have relevant health conditions, take regular medication, or are pregnant or breastfeeding.

Frequently Asked Questions

Does ashwagandha lower cortisol?

Clinical trials and a 2025 meta-analysis of seven RCTs (Albalawi et al., n=488) found a statistically significant reduction in serum cortisol levels in ashwagandha groups compared to placebo (−1.16 µg/dL, P < 0.001). This is a real and consistent finding across the literature. However, the same meta-analysis found no statistically significant effect on perceived stress as measured by the Perceived Stress Scale — highlighting that a biomarker reduction and a change in subjective experience do not always move together.

Does ashwagandha help with anxiety?

A 2025 meta-analysis in BJPsych Open (Bachour et al., 15 RCTs, n=873) found that ashwagandha supplementation significantly reduced anxiety compared to placebo on the Hamilton Anxiety Rating Scale. This is one of the more robust findings in the ashwagandha literature, though the standard compliance caveat applies: ashwagandha has no EFSA-authorised health claim for anxiety in the UK, and this research cannot be used as a product claim.

How long do ashwagandha trials typically run?

Most published trials run for 6–12 weeks. A 12-month prospective safety study (Salve et al., 2025) provides reassurance on extended use at standard doses in healthy adults, but most efficacy data comes from shorter durations. Whether effects are maintained, increase, or diminish over longer periods is not yet well characterised.

Why is there a difference between cortisol results and perceived stress results?

Cortisol is an objective biological measurement; perceived stress is a self-report score. The 2025 Albalawi meta-analysis found ashwagandha had a significant effect on the former but not the latter. This likely reflects the complexity of stress as a lived experience it involves cognitive appraisal, social context, sleep, and many other factors beyond what a hormone level captures. The disconnect is genuine and important for setting realistic expectations.

Is ashwagandha safe to take every day?

At standard doses from root-only standardised extracts (typically 300–600mg per day), the safety profile is generally considered acceptable for healthy adults without contraindications, based on short-term trial data and one 12-month safety study. Caution is warranted at higher doses over extended periods due to emerging case reports of HPA axis suppression. Ashwagandha should be avoided during pregnancy and by those with thyroid or liver conditions. Consult a GP if you have relevant health circumstances.

What is the difference between ashwagandha and just managing stress through lifestyle?

Ashwagandha research is conducted in the context of standard care participants are not asked to abandon lifestyle stress management. The evidence suggests it may complement not replace approaches like sleep, exercise, reduced workload, and social support. No supplement substitutes for addressing the source of chronic stress.