Ashwagandha (Withania somnifera) is the most clinically researched adaptogen in existence. While other adaptogens have long traditional histories and promising early research, ashwagandha has something rarer: a consistent body of well-designed human trials with measurable outcomes. If you're only going to take one adaptogen, the evidence points here.
What It Does to Cortisol
The primary mechanism that makes ashwagandha valuable is its effect on the HPA axis — the system governing cortisol production. Multiple randomised controlled trials have found statistically significant reductions in serum cortisol in adults taking standardised ashwagandha extract. A 2019 study found 240mg per day reduced morning cortisol by around 23% versus placebo over 60 days. A 2012 study with 300mg twice daily found 28% reduction alongside 44% improvement in perceived stress scores.
This isn't just numbers on a lab report. The downstream effects of lower chronic cortisol are meaningful: better sleep, reduced anxiety, improved body composition (cortisol promotes fat storage), and more stable mood across the day.
The KSM-66 and Sensoril Question
Most of the strong clinical evidence uses one of two branded extracts: KSM-66 (root-only extract, standardised to 5% withanolides) or Sensoril (combined root and leaf, higher withanolide content). Both are well-researched. Generic "ashwagandha" supplements without specifying extract type or withanolide percentage are harder to evaluate — quality varies considerably.
Key Facts
- Standard effective dose: 300–600mg of standardised extract daily
- Key compounds: withanolides (look for 5% standardisation minimum)
- Best-evidenced extracts: KSM-66 and Sensoril
- Effects on cortisol typically measurable within 4–8 weeks
- Also studied for testosterone, muscle recovery, and thyroid function
Sleep and Recovery
One underappreciated benefit of ashwagandha is its effect on sleep quality. It contains triethylene glycol, a compound that appears to promote non-REM sleep. A 2020 study found that 600mg KSM-66 before bed significantly improved sleep quality, sleep onset latency, and morning alertness versus placebo. For people under chronic stress whose sleep has degraded, this is a meaningful benefit that most adaptogen marketing doesn't emphasise enough.
Ashwagandha is one of the few adaptogens where the evidence is strong enough to say: if you're chronically stressed and sleeping poorly, this is worth trying before anything else.
Who Should Be Cautious
Ashwagandha has thyroid-stimulating properties and should be used cautiously by anyone with hyperthyroidism or on thyroid medication. It's also contraindicated during pregnancy. For most healthy adults under chronic stress, it's well-tolerated with no serious adverse effects documented in trials.