One of the few herbs with real human evidence — it lowers cortisol and modestly supports testosterone, sleep and recovery.
Ashwagandha is an adaptogen — a plant that helps regulate the stress response. Its most consistent effect is lowering cortisol, the stress hormone that competes with testosterone for resources and disrupts sleep. By easing that load it can indirectly support testosterone, mood, sleep and recovery.
For the standardised KSM-66 extract, the evidence is genuinely promising. In a controlled trial, 600 mg/day of ashwagandha root extract significantly raised free and total testosterone in men, with better strength and faster recovery. Longer-term data back the safety: over 12 months at 600 mg/day, KSM-66 modestly lowered cortisol and raised testosterone with no adverse effects on liver, kidney or thyroid function and no serious adverse events. The effect is a real, moderate nudge — not a transformation.
Men who are 'tired but wired', sleeping poorly, under chronic stress, or training hard tend to notice the most — calmer mood, better sleep and steadier energy often arrive before any hormonal change.
300–600 mg/day of KSM-66, standardised to about 5% withanolides. There's no formal upper limit, but more is not better — stick to the studied range. It's been used safely for up to 12 months; some people prefer planned breaks.
Take it with food. An evening dose suits most men because it supports sleep; if you use 600 mg, splitting it morning and evening is fine. Benefits build over 2–8 weeks, so give it time.
Higher-than-needed doses mainly cause drowsiness and stomach upset. The more important signal is rare but real: isolated case reports have linked ashwagandha to moderate liver injury, typically with poorly characterised products. Stop and seek advice if you notice unusual fatigue, dark urine or yellowing of the skin or eyes.
Magnesium (evening, for sleep), vitamin D3, and creatine for training. Take care stacking it with other sedating supplements.
Ashwagandha can add to the effect of sedatives, benzodiazepines and alcohol, may increase thyroid activity, and is generally advised against in pregnancy. Clear it with your doctor if you take thyroid medication or have a thyroid or autoimmune condition.
Anyone pregnant or breastfeeding (avoid), with a thyroid or autoimmune condition, taking sedatives or thyroid medication, or with liver concerns. Discuss long-term daily use with a doctor.
This matters more than for most supplements. Choose a root-only, standardised extract — KSM-66 or Sensoril — and avoid cheap leaf or whole-plant extracts, which contain more of the compounds implicated in liver and toxicity concerns. Look for a stated withanolide percentage and third-party testing (Informed Sport, NSF).
Ashwagandha is among the few herbs with real human evidence for stress, sleep and a modest testosterone benefit. Use a standardised root extract at 300–600 mg/day, mind the thyroid and sedative interactions, avoid it in pregnancy, and choose quality over price.
Wankhede et al., J Int Soc Sports Nutr (2015); Salve et al., 12-month safety study, Phytotherapy Research (2025); Björnsson et al., liver-injury case series (2020); NIH/NCCIH; Mayo Clinic.
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Based on guidance from the NHS, NICE, Cleveland Clinic and peer-reviewed research.
General information, not a substitute for personal medical advice — always consult your doctor or a qualified health professional before making health decisions. If you are pregnant, breastfeeding, trying to conceive, under 18, or taking medication, speak to your doctor before starting any supplement.