Ashwagandha and Cortisol: What the Clinical Evidence Actually Shows

Cortisol is not the enemy. It is a necessary hormone that regulates energy, immune response, and the body's reaction to acute stress. The problem arises when cortisol stays elevated for extended periods, driven often by chronic psychological stress, poor sleep, or overtraining.

Ashwagandha (Withania somnifera) has been used in Ayurvedic medicine for centuries as an adaptogen, a class of plant compounds that help the body resist and adapt to stress. Over the past decade, that traditional use has been tested rigorously in randomised controlled trials. The findings are consistent: ashwagandha supplementation produces measurable, statistically significant reductions in serum cortisol.

The key question is not whether it works, but how, at what dose, and which extract delivers the best results.

How Ashwagandha Influences Cortisol

Ashwagandha does not block cortisol directly. Its primary mechanism operates through the hypothalamic-pituitary-adrenal (HPA) axis, the hormonal cascade that governs the stress response.

When the brain perceives a threat, the hypothalamus signals the pituitary gland, which in turn triggers the adrenal glands to release cortisol. In people under chronic stress, this system becomes dysregulated, producing cortisol at inappropriately high levels even in the absence of acute threat.

The active compounds in ashwagandha, primarily withanolides (steroidal lactones), appear to modulate this axis by:

• Reducing the sensitivity of the HPA axis to perceived stress signals
• Lowering the baseline output of cortisol from the adrenal glands
• Supporting GABA receptor activity, which has a calming effect on the nervous system
• Reducing markers of inflammation that are associated with HPA dysregulation

The result is not sedation or blunted alertness. It is a recalibration of the stress response toward a more appropriate baseline.

What the Clinical Trials Show

The evidence base for ashwagandha and cortisol is substantially stronger than for most adaptogens. Multiple randomised, double-blind, placebo-controlled trials have measured serum cortisol directly, rather than relying on self-reported stress scores.

The 2019 Chandrasekhar et al. Study

One of the most cited trials is the 2019 study published in Medicine (PMID: 31517876), which enrolled 60 adults with self-reported high stress. Participants received either 240 mg/day of ashwagandha extract or a placebo for 60 days. The ashwagandha group showed a statistically significant reduction in morning serum cortisol compared with placebo (P < 0.05), along with improvements in sleep quality and perceived stress scores.

The Langade et al. 2019 Trial (KSM-66)

A double-blind RCT published in Cureus (PMID: 31728244) tested 300 mg twice daily of KSM-66 ashwagandha root extract in adults with insomnia and anxiety. After 10 weeks, the ashwagandha group showed significant improvements in sleep quality and stress markers. Serum cortisol was meaningfully reduced compared with placebo, with the effect size increasing over the course of supplementation.

The 60-Day High-Dose Trial

A well-controlled trial examining 600 mg/day of ashwagandha root extract (PMID: 23439798) found cortisol levels dropped from a mean of 9.04 µg/dL to 6.34 µg/dL in the treatment group over 60 days, representing a 27.9% reduction compared to just 7.9% in the placebo group (P < 0.0001). Perceived stress scores fell by 44% versus 5.5% in placebo participants.

2024 Meta-Analysis

The most comprehensive synthesis to date, a 2024 meta-analysis published on PubMed that incorporated 7 RCTs and 488 participants, found a pooled cortisol reduction of **-**1.16 µg/dL (95% CI: -1.64 to -0.69, P < 0.001) with ashwagandha supplementation. This effect held across different doses and extract types, confirming the cortisol-lowering action is a reproducible finding rather than an artefact of individual studies.

Key takeaway: Across multiple independent trials, ashwagandha consistently reduces serum cortisol by approximately 23-28% compared to placebo, with effects becoming more pronounced over 8-12 weeks of supplementation.

KSM-66 vs Sensoril: Does the Extract Type Matter?

Not all ashwagandha supplements are equivalent. The two most clinically studied proprietary extracts, KSM-66 and Sensoril, differ in meaningful ways.

KSM-66

KSM-66 is a root-only extract standardised to approximately 5% withanolides. It is the most extensively researched ashwagandha extract, with around 30 human clinical trials supporting its use. Because it uses only the root, it avoids the mildly stimulating alkaloids found in ashwagandha leaves, making it a cleaner option for those sensitive to stimulants. The cortisol reduction data referenced above (27.9% in 60 days) comes primarily from KSM-66 trials.

Sensoril

Sensoril uses both root and leaf, resulting in a higher withanolide concentration (approximately 10%) at a lower dose. It has been studied in 15 clinical trials and shows particular strength in relaxation and sleep quality. One study found an 88% reduction in anxiety symptoms ****in the Sensoril group compared to 50% in the placebo group. Its higher bioavailability makes it well-suited for evening supplementation and sleep-focused formulations.

Problem: Using the leaf causes safety concerns for liver toxicity, and it is best practice to use KSM-66.

Dosage and Timing: What the Evidence Supports

Clinical trials have used a range of doses, and the data provide reasonably clear guidance.

• 250 mg/day: Produces statistically significant cortisol reductions (P < 0.05). A viable entry-level dose, particularly for those new to ashwagandha.
• 300-600 mg/day: The most commonly studied range. Trials at 600 mg/day show stronger effects (P < 0.01) and are generally considered the clinical sweet spot.
• Split dosing: Several trials used twice-daily dosing (e.g., 300 mg in the morning, 300 mg in the evening), which may support more consistent HPA axis modulation throughout the day.

Duration matters as much as dose. Across the trials, cortisol reductions become more pronounced over time. Most studies show meaningful effects by week 4, with peak reductions observed at 8-12 weeks. Ashwagandha is not an acute intervention; it works through sustained modulation of the stress response system.

Timing considerations:

• Morning dosing supports daytime stress resilience and energy
• Evening dosing (particularly with Sensoril) supports sleep quality and overnight cortisol regulation
• Taking ashwagandha with food may improve tolerability and absorption

Who should exercise caution:

• Pregnant or breastfeeding women (insufficient safety data)
• Individuals with thyroid conditions (ashwagandha may influence thyroid hormone levels)
• Those taking immunosuppressants, sedatives, or thyroid medications (potential interactions)

As with any supplement, it is advisable to consult a GP or registered nutritionist before starting, particularly for those with existing health conditions or taking medication.

References

The following PubMed-indexed studies were referenced in this article:

1. Chandrasekhar K, et al. (2019). A prospective, randomised 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. Medicine. PMID: 31517876
2. Langade D, et al. (2019). Efficacy and Safety of Ashwagandha (Withania somnifera) Root Extract in Insomnia and Anxiety: A Double-blind, Randomized, Placebo-controlled Study. Cureus. PMID: 31728244
3. Chandrasekhar K, et al. (2012). A prospective, randomised 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 Journal of Psychological Medicine. PMID: 23439798
4. Pratte MA, et al. (2014). An Alternative Treatment for Anxiety: A Systematic Review of Human Trial Results Reported for the Ayurvedic Herb Ashwagandha (Withania somnifera). Journal of Alternative and Complementary Medicine. PMID: 25405876
5. Verma N, et al. (2021). Safety of Ashwagandha Root Extract: A Randomized, Placebo-Controlled, study in Healthy Volunteers. Complementary Therapies in Medicine. PMID: 33338583