Ashwagandha
Ashwagandha (Withania somnifera) is an Ayurvedic herb whose root contains steroidal lactones called withanolides. Most of its human evidence comes from a handful of small, eight-week trials of branded extracts, largely run or supported by the companies that sell them, reporting lower perceived stress and serum cortisol. It also raises thyroid hormone and has a documented, if rare, link to liver injury.
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What It Does
The proposed mechanisms, GABA-like activity and dampening of the hypothalamic-pituitary-adrenal axis, come mainly from animal studies. The human trials measure outcomes rather than mechanism.
In the first widely cited trial, 64 adults with chronic stress took 300 mg of a root extract (KSM-66) twice daily for 60 days; stress scale scores and serum cortisol fell compared with placebo (Chandrasekhar 2012). Salve and colleagues gave 60 adults 250 or 600 mg a day for eight weeks and reported lower perceived stress and cortisol, with better sleep (Salve 2019). Lopresti and colleagues tested a root and leaf extract (Shoden) at 240 mg a day in 60 adults; anxiety scores fell modestly and morning cortisol dropped, while the change in testosterone was not significant against placebo (Lopresti 2019). The direction is consistent across trials. They are also small, short, mostly conducted in India, and each tests a different proprietary extract, which makes pooling difficult. Effects on sleep, athletic performance, and male fertility come from similarly small trials.
Thyroid stimulation is a real effect. In 50 people with subclinical hypothyroidism, 600 mg a day for eight weeks lowered TSH and raised T3 and T4 (Sharma 2018). That is a hazard for anyone with hyperthyroidism or taking levothyroxine, and case reports describe ashwagandha-associated thyrotoxicosis.
Liver injury is rare but documented. A case series from Iceland and the US Drug-Induced Liver Injury Network described cholestatic jaundice beginning weeks to months after starting ashwagandha, with recovery after stopping (Björnsson 2020). Ashwagandha should be avoided in pregnancy and used cautiously with sedatives, immunosuppressants, and thyroid medication.
Forms and Bioavailability
Absorption ratings are broad tiers. Head-to-head human trials rarely support a finer ranking among well-absorbed forms.
| Form | Absorption | Typical dose | Cost | Labels |
|---|---|---|---|---|
| Ashwagandha Root PowderWithania somnifera root, whole root powder | VariableWhole dried root containing withanolides and alkaloids at variable, unstandardized concentrations. | 3-6 g daily in traditional use | Low | |
| Ashwagandha Root Extract (e.g. KSM-66)KSM-66, standardized root extract | VariableConcentrated root extract standardized to withanolide content. Most randomized trials on stress and sleep used root-only extracts. | 250-600 mg daily | Moderate | 423 |
| Ashwagandha Root and Leaf Extract (e.g. Sensoril)Sensoril, Shoden | VariableExtract of root and leaf, standardized to a higher withanolide glycoside content than root-only extracts. Used at lower milligram doses. | 125-250 mg daily | Moderate |
Labels column: number of labels named as ashwagandha products that list this form. A product can list more than one form, and some labels do not state a form at all.
Root powder is the unprocessed herb with low and unstandardized withanolide content. Trial doses of extracts do not translate to it. KSM-66 is a root-only extract standardized to at least 5% withanolides. Sensoril and Shoden use root and leaf and are standardized to higher withanolide percentages, which allows lower doses. Leaf contains more withaferin A, a withanolide that is cytotoxic in cell studies; leaf is not part of traditional Ayurvedic preparations, and some regulators restrict it. Withanolide percentages are measured by different methods and are not comparable across brands.
Typical Dosing
Clinical trials have mostly used 250-600 mg per day of standardized root extract for up to about 3 months.
What to Look For
Look for a named, standardized extract with milligrams per capsule and withanolide content stated, ideally with the assay method (HPLC). Match the product to the trial you are relying on: 300-600 mg a day for KSM-66, smaller doses for root and leaf extracts.
Use it for a defined period, such as eight to twelve weeks, and stop if you notice jaundice, dark urine, itching, or symptoms of an overactive thyroid such as palpitations, tremor, or heat intolerance. Anyone with thyroid disease should check thyroid levels after starting.
Red flags: gummies with 100 mg or less of unstandardized powder, "adaptogen" blends that hide the ashwagandha dose, and testosterone claims.
Ashwagandha Root Extract (e.g. KSM-66)
The best-studied preparation. Expect a modest effect on self-rated stress, from trials that were small and mostly industry supported.
What to look for: KSM-66 or another named root extract, 300-600 mg a day, withanolide content stated with its assay method.
Find on iHerb Affiliate linkAshwagandha Root and Leaf Extract (e.g. Sensoril)
Sensoril and Shoden include leaf, which raises both the withanolide percentage and the withaferin A content. Separate, smaller evidence base.
What to look for: The dose used in that extract's own trials, such as 240 mg for Shoden. Do not compare withanolide percentages across brands.
Find on iHerb Affiliate linkAshwagandha Root Powder
Cheap and unstandardized. Not what the trials used.
What to look for: Skip it unless you prefer traditional preparations; the withanolide dose per gram is unknown.
Find on iHerb Affiliate linkProducts on Titrate
2,581 of the 214,745 labels in the NIH Dietary Supplement Label Database list ashwagandha as an active ingredient (1,512 on market). 649 are sold as ashwagandha products by name.
Top on-market labels, ranked by label completeness and simplicity:
- KSM-66 Ashwagandha
- KSM-66 Ashwagandha 500 mg
- Organic Ashwagandha
- Ashwagandha with BioPerine
- KSM-66 Ashwagandha
Ashwagandha does not have its own search category yet. Each product above links to its full label in the NIH database.
Related Tools
References
NIH Office of Dietary Supplements. Ashwagandha: Is It Helpful for Stress, Anxiety, or Sleep? Fact Sheet for Health Professionals.
Chandrasekhar K, Kapoor J, Anishetty S. A prospective, randomized double-blind, placebo-controlled study of safety and efficacy of a high-concentration full-spectrum extract of ashwagandha root in reducing stress and anxiety in adults. Indian J Psychol Med. 2012;34(3):255-262.
Sharma AK, Basu I, Singh S. Efficacy and Safety of Ashwagandha Root Extract in Subclinical Hypothyroid Patients: A Double-Blind, Randomized Placebo-Controlled Trial. J Altern Complement Med. 2018;24(3):243-248.
Salve J, et al. Adaptogenic and Anxiolytic Effects of Ashwagandha Root Extract in Healthy Adults: A Double-blind, Randomized, Placebo-controlled Clinical Study. Cureus. 2019;11(12):e6466.
Lopresti AL, et al. An investigation into the stress-relieving and pharmacological actions of an ashwagandha (Withania somnifera) extract: A randomized, double-blind, placebo-controlled study. Medicine (Baltimore). 2019;98(37):e17186.
Björnsson HK, et al. Ashwagandha-induced liver injury: A case series from Iceland and the US Drug-Induced Liver Injury Network. Liver Int. 2020;40(4):825-829.
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