Ashwagandha
What it is
Ashwagandha (Withania somnifera) is a root extract from Ayurvedic medicine with increasing use in Western supplement markets. The active constituents are believed to include withanolides, though the relative contribution of individual compounds to observed effects has not been established. Most clinical evidence uses one of two proprietary standardised extracts: KSM-66 (root-only, standardised to at least 5% withanolides) or Sensoril (root and leaf, standardised to at least 10% withanolides). Evidence from these trials should not be assumed to apply to non-standardised or generic products, which vary considerably in active constituent content.
A significant proportion of the trial evidence is industry-funded by the manufacturers of KSM-66 or Sensoril. Effect sizes in independent trials are systematically smaller than in industry-funded work. This limitation runs through the evidence base and is reflected throughout this entry.
What the evidence shows
Stress reduction is the most consistently supported outcome. Multiple randomised controlled trials using KSM-66 or Sensoril at doses of 300-600mg/day demonstrate reductions in self-reported stress on validated rating scales including the Perceived Stress Scale. Effect sizes across trials are in the range of SMD 0.4-0.7, which is moderate by conventional thresholds but should be interpreted with caution given the high proportion of industry-funded work and short trial durations of 6-12 weeks. The signal is real; the magnitude is uncertain.
Sleep quality in individuals with baseline sleep disturbance shows a consistent directional signal across several trials. Improvements in sleep onset latency, total sleep time, and sleep efficiency have been reported. Effects are most consistent in individuals with self-reported sleep problems at baseline; evidence in good sleepers is limited.
Cortisol reductions of approximately 15-30% from baseline have been reported in stressed populations. These estimates vary widely across trials and are sensitive to measurement methodology, assay type, and timing of sampling. Cortisol is best understood here as an exploratory biomarker, a consistent directional finding in stressed populations, but with uncertain clinical translation.
What the evidence does not show
Physical performance effects are substantially smaller and less consistent than established ergogenic aids such as creatine or caffeine. The available evidence does not support ashwagandha as a meaningful performance supplement by current standards.
Cognitive effects vary widely depending on the task and population studied. The evidence is too heterogeneous and too reliant on industry-funded small trials to support confident claims.
Testosterone effects in healthy men with normal baseline testosterone are small and inconsistently replicated. The more consistent signal is in sub-fertile men or those with low baseline testosterone, where modest improvements in sperm parameters and hormone levels have been reported.
Extract type matters
Evidence from KSM-66 or Sensoril trials is not transferable to non-standardised ashwagandha without direct comparative data. Many consumer products use generic root powder with variable withanolide content at uncertain doses. Where a specific outcome is the goal, product selection should match the extract type and dose used in the relevant evidence base.
Who the evidence applies to
The evidence is most consistent in individuals with genuinely elevated baseline stress or sleep disturbance. Those with low stress or good sleep are less likely to show measurable benefit.
The testosterone and fertility evidence applies most clearly to sub-fertile men or those with documented hormonal concerns. Evidence in healthy men with normal parameters is insufficient.
Women in perimenopause and menopause represent an emerging relevant population, with early trial evidence for stress, sleep, and symptom relief in this life stage.
Safety and contraindications
Ashwagandha is generally well-tolerated at doses used in clinical trials. However, rare but serious cases of liver injury have been reported, with incidence unknown due to the absence of denominator data. Any symptoms of liver dysfunction, jaundice, abdominal pain, dark urine, should prompt discontinuation and clinical assessment. Individuals with pre-existing liver conditions should not use ashwagandha without medical supervision.
Ashwagandha is contraindicated in pregnancy due to traditional use as a uterine stimulant. It should not be used during breastfeeding without clinical review.
Rare cases of clinically significant thyroid effects have been reported. Individuals with hyperthyroidism or those taking thyroid medication should seek clinical advice before use. Ashwagandha may potentiate sedative medications. Caution is appropriate in autoimmune conditions.
What can reasonably be concluded
Ashwagandha has a genuine and growing evidence base for stress reduction and sleep quality improvement, particularly in individuals with elevated baseline stress or sleep disturbance. The Moderate rating reflects a real signal, but confidence is reduced by systematic industry funding bias, small trial sizes, and short durations.
Extract standardisation matters: KSM-66 and Sensoril are the evidence-based choices. Non-standardised products cannot be assumed equivalent.
The safety profile is generally acceptable at normal doses but includes rare serious risks, particularly hepatotoxicity, that are often absent from commercial communications and should be part of any honest assessment.
Where evidence is limited or outcomes are uncertain, conclusions should be treated as provisional and subject to revision as the evidence base develops.