The Best Ashwagandha Supplements: What the Research Says About Form and Dose

Ashwagandha (Withania somnifera) is one of the better-studied adaptogens available. While the supplement industry is filled with herbs that have pre-clinical (cell or animal) evidence only, ashwagandha has multiple randomized controlled trials in humans examining stress, anxiety, and sleep specifically.

That said, not all ashwagandha products are the same. The research that produces consistent results uses standardized extracts at specific doses. Understanding the difference matters when evaluating what’s on shelves.

How we evaluate products in this guide

These recommendations are based on whether the product uses an extract that matches what clinical studies used, whether the dose aligns with studied amounts, and whether there is third-party testing confirming label accuracy and purity. We do not conduct hands-on product testing.

Why standardization matters

Ashwagandha’s active compounds are primarily withanolides, a class of steroidal lactones. Raw ashwagandha powder has variable withanolide content depending on the part of the plant, growing conditions, and processing. A product with 500 mg of unstandardized root powder could have dramatically different withanolide content than one using a 5%-standardized extract.

Clinical trials typically specify the extract used and its standardization. When a trial shows a benefit, that benefit is associated with a specific withanolide dose, not just “ashwagandha.” Products that don’t specify the extract type or standardization level are harder to compare to that evidence.

The two most used standardized extracts in research are:

KSM-66: A full-spectrum root extract standardized to at least 5% withanolides, developed by Ixoreal Biomed. It’s the most studied ashwagandha extract by number of published trials.

Sensoril: A root-and-leaf extract standardized to at least 10% withanolides, developed by Natreon. It uses a different extraction process and has its own body of clinical research.

Both have evidence for stress and anxiety. KSM-66 has been studied more extensively for physical performance applications as well. Sensoril is used at a lower dose (125–250 mg vs. 300–600 mg) because of higher withanolide concentration.

What the research shows

A 2019 randomized, double-blind, placebo-controlled trial in Medicine tested KSM-66 at 240 mg daily in adults with self-reported elevated stress. After 60 days, the ashwagandha group showed significantly reduced cortisol levels (by approximately 23%), lower scores on validated stress scales, and better sleep quality compared to placebo.

A 2012 trial in the Indian Journal of Psychological Medicine tested 300 mg of KSM-66 twice daily (600 mg total) in adults with chronic stress. After 60 days, the ashwagandha group had significant reductions in scores on the Perceived Stress Scale, lower serum cortisol, and improvements in a range of stress-related biomarkers. All differences were statistically significant compared to placebo.

For Sensoril, a 2008 trial in the Journal of the American Nutraceutical Association found that 125 mg and 250 mg doses both improved scores on anxiety and general wellbeing measures, with the 250 mg dose producing more consistent effects.

A 2021 Cochrane-adjacent systematic review of ashwagandha for anxiety and stress found that the totality of evidence was promising but noted that most trials were small, short in duration, and industry-funded to varying degrees, limiting confidence in effect size estimates.

Products that use the studied extracts

Products using KSM-66

Thorne Ashwagandha provides 300 mg of KSM-66 per capsule (600 mg per serving at the clinical dose). Thorne holds NSF International certification and uses no unnecessary fillers. It’s a clean, well-formulated product from a brand with strong manufacturing standards.

Jarrow Formulas Ashwagandha uses KSM-66 at 300 mg per capsule and is third-party tested. Widely available and priced accessibly.

Gaia Herbs Ashwagandha Root uses a liquid phyto-capsule format with a standardized KSM-66 extract. Gaia is one of the more transparent brands in the herbal supplement space and publishes testing data via their MeetYourHerbs traceability program.

Products using Sensoril

NOW Foods Ashwagandha offers a Sensoril formulation at 125 mg per capsule with a USP-certified manufacturing facility and good price point.

Pure Encapsulations Ashwagandha uses Sensoril at 250 mg, with NSF GMP certification and a very clean formulation.

What to avoid

Generic ashwagandha products without any specified extract type or standardization percentage are harder to evaluate against the clinical evidence. The product may work, but you have no way to compare what’s in it to the doses and extracts used in studies.

Avoid products with very high doses marketed as “more powerful.” The clinical evidence doesn’t support doses above 600 mg of a standardized extract for most applications, and higher doses increase the likelihood of side effects.

When to expect results and how to take it

Effects on stress, perceived anxiety, and sleep quality typically appear within 4–8 weeks of consistent daily use in the clinical literature. Cortisol changes are documented at 60 days in most trials.

Ashwagandha can be taken with or without food. Some people find taking it in the evening works better for the sleep benefits; others take it in the morning to manage daytime stress. The research doesn’t strongly favor one timing over the other.

Safety and who should avoid it

Ashwagandha has a good safety profile at standard doses in healthy adults. The most commonly reported side effects are mild GI discomfort (nausea, loose stools), which typically resolves.

It should be avoided during pregnancy. Animal studies have shown potential abortifacient effects at high doses, and there’s insufficient human safety data to recommend it during pregnancy.

It may interact with thyroid medications (ashwagandha can increase thyroid hormone levels), immunosuppressants, and sedative medications. If you take any of these, discuss with your doctor before starting.

Rare reports of liver injury associated with ashwagandha use have appeared in case literature. These are uncommon but worth noting, particularly at high doses or in people with underlying liver conditions.

The bottom line

Ashwagandha, specifically standardized extracts like KSM-66 and Sensoril at studied doses, has more clinical evidence for reducing stress, cortisol, and anxiety symptoms than most adaptogens. The effect isn’t dramatic, but it’s consistent across multiple independent trials and appears to build with sustained use over 8–12 weeks.

If you’re evaluating ashwagandha products, prioritize ones that specify the extract type and standardization percentage, and match the dose to the 300–600 mg range used in research. Products using raw or unstandardized powder at equivalent milligrams are not equivalent.