science
Ashwagandha: The Most-Studied Adaptogen
11 min read
Ashwagandha (Withania somnifera) is the most clinically supported herbal adaptogen. Modern research has converged on three robust outcomes: cortisol reduction, anxiety reduction, and sleep quality.
The Standardized Extract
KSM-66 and Sensoril are the two most-studied extracts. KSM-66 (Ixoreal) is standardized to ≥5% withanolides via a full-spectrum extract from roots only. It is the version used in most published RCTs.
Dose-Response
Most studies use 300–600 mg/day, taken once or split AM/PM. Higher doses (1,000+ mg) do not consistently outperform 600 mg, but do increase drowsiness.
Cortisol
A 2019 RCT (Salve et al.) showed a ~28% reduction in morning serum cortisol after 8 weeks at 600 mg/day KSM-66. The effect compounds with consistent dosing — sporadic use shows much smaller effects.
Testosterone in Men
Lopresti et al. (2019) demonstrated a meaningful increase in serum testosterone in men under 50 at 600 mg/day. No equivalent effect in women.
Who Should Skip It
Hyperthyroidism (ashwagandha can elevate T4). Pregnancy or trying to conceive. Active autoimmune flare — withanolides modulate immune function in ways that can be unpredictable. Anyone on sedatives or hypnotics — ashwagandha potentiates them.