Ashwagandha (KSM-66)
Adaptogen clinically proven to reduce cortisol by 30%
What is Ashwagandha (KSM-66)?
Ashwagandha (Withania somnifera) is a small shrub in the nightshade family, used for over 3,000 years in Ayurvedic medicine. 'KSM-66' refers to a specific root extract standardised to ≥5% withanolides (the active compounds), produced by Ixoreal Biomed. It's the most clinically studied ashwagandha extract, with over 22 gold-standard clinical trials.
How it works
Withanolides, the bioactive constituents, act primarily on the hypothalamic-pituitary-adrenal (HPA) axis — the stress response system. They reduce the production and signalling of cortisol by modulating heat shock protein 90 (Hsp90) chaperone activity, which normally stabilises the cortisol receptor. Additionally, withanolides have GABA-mimetic activity (binding GABA-A receptors) and modulate thyroid hormone levels.
What the evidence shows
A 2012 double-blind RCT (Chandrasekhar et al., Indian J Psychol Med) showed 300mg KSM-66 twice daily for 60 days reduced serum cortisol by 27.9%, reduced stress and anxiety scores significantly, and improved quality of life. A 2015 crossover RCT showed significant improvements in muscle strength and recovery. 2019 and 2020 trials confirmed sleep benefits (total sleep time, sleep efficiency, morning alertness).
When to expect results
Subtle shifts in evening mood. Some people notice they feel slightly calmer in stressful situations.
Stress response becoming more modulated. Sleep quality improving. The anxious 'edge' less pronounced.
Measurable cortisol reduction — the point used in most clinical trials. Significant improvements in stress resilience and sleep quality scores.
Full adaptive benefit established. Sustained HPA axis regulation. Most people report a distinctly calmer baseline.
Dosing
Clinical trials use 300mg KSM-66 extract twice daily (600mg total). This is the standard recommendation. Some trials use 300mg once daily with good effect. Results accumulate over 6–8 weeks — most trials use 8 weeks as primary endpoint. Don't judge before week 4.
Forms to choose
KSM-66 and Sensoril are the two most clinically studied extracts. KSM-66 uses only root (traditional use); Sensoril uses root and leaf. Both are effective. Avoid products that don't specify the extract type — generic ashwagandha powder may be significantly less potent.
Who benefits most
People with chronic stress, anxiety, poor sleep driven by stress (not circadian issues), athletes wanting to reduce training-induced cortisol elevation, people with subclinical hypothyroidism (may improve thyroid function), men with low testosterone (several trials show modest increase).
Who should avoid / caution
Pregnant women (animal studies suggest uterotonic effects), people with thyroid conditions without GP monitoring, people with autoimmune conditions (may stimulate immune activity), people with nightshade sensitivity.
Interactions & stacking
Complementary stress/sleep mechanisms — cortisol reduction (ashwagandha) + GABA activation (magnesium). Popular combination.
Both reduce anxiety via different pathways. L-theanine for acute calm; ashwagandha for long-term HPA regulation.
May affect thyroid hormone levels. Monitor T3/T4 if on levothyroxine or antithyroid medication.
May stimulate immune activity — consult specialist if on immunosuppressive therapy.
Safety & side effects
Generally well-tolerated. Most common: mild GI discomfort, particularly on empty stomach — take with food. Rare: liver enzyme elevation reported in a handful of case reports at very high doses. People with thyroid conditions should monitor levels, as ashwagandha may increase T3/T4.
Shop Ashwagandha (KSM-66)
Browse our UK-sourced, third-party tested ashwagandha (ksm-66) products.
Build your complete supplement stack
Our quiz tells you exactly which supplements to pair with this one
Find your perfect stack in 60 seconds — no email required.
This information is for educational purposes only and does not constitute medical advice. Always consult your GP or a qualified healthcare professional before starting any new supplement, particularly if you are pregnant, breastfeeding, have a medical condition, or are taking prescription medication.