The short version
- The most-cited ashwagandha stress trial used 600mg a day, given as 300mg twice daily, in 64 adults for 60 days, and reported significantly reduced stress and anxiety scores alongside reduced serum cortisol.
- The one trial that varied the dose found both 250mg and 600mg a day beat placebo over eight weeks, but perceived stress and serum cortisol fell far more decisively at 600mg.
- Ashwagandha trials used concentrated root extract rather than raw ground root, so a label reading 1,000mg of root describes a less concentrated material than 600mg of extract.
- A 2020 case series described five patients who developed jaundice and liver injury attributed to ashwagandha-containing supplements, after a latency of two to twelve weeks.
- Ashwagandha can influence thyroid hormone levels, which makes it a doctor conversation for anyone taking levothyroxine or living with a diagnosed thyroid condition.
Ashwagandha is one of the few botanicals with genuinely repeatable human trial data on stress. It's also one of the most under-dosed ingredients on the shelf, which is why two bottles with the same word on the front can behave completely differently.
The trial most often cited is Chandrasekhar and colleagues, 2012, in the Indian Journal of Psychological Medicine. Sixty-four adults with a history of chronic stress took either placebo or 300mg twice daily — 600mg total — for 60 days. The supplemented group showed significantly reduced stress and anxiety scores alongside significantly reduced serum cortisol.
That 600mg figure is the number that matters. It is the dose the research used. A capsule containing 150mg is not a smaller version of this study; it's a different intervention that hasn't been tested the same way.
Later work supports the direction. A 2019 randomised, double-blind, placebo-controlled study by Lopresti and colleagues examined stress-relieving and pharmacological actions of an ashwagandha extract, and a 2023 randomised trial found a standardised root extract alleviated stress and anxiety while modulating stress hormones.
The one trial that actually varied the dose
Almost every ashwagandha study tests a single dose against placebo. That design tells you whether the herb does something. It cannot tell you how much you need, which is the only question a shopper standing in front of a shelf actually has. Salve and colleagues, publishing in Cureus in 2019, ran the more useful experiment. Sixty stressed but otherwise healthy adults — all with a baseline Perceived Stress Scale score above 20 — were randomised three ways for eight weeks: 125mg twice daily, 300mg twice daily, or an identical placebo. In plain numbers, 250mg a day against 600mg a day against nothing.
Both real doses beat placebo, and that is the honest headline. The separation shows up in how convincingly. Perceived stress fell at 250mg a day (P < 0.05) and fell harder at 600mg a day (P < 0.001). Serum cortisol dropped at 250mg a day (P < 0.05) and dropped far more decisively at 600mg a day (P < 0.0001). Participants on ashwagandha also reported better sleep quality than those on placebo.
Read that carefully, because it cuts both ways and we're not going to pretend otherwise. A genuinely low dose is not nothing. But the strongest results cluster at the dose most labels fail to reach, and there is no trial anywhere showing that 150mg does what 600mg does. Both of these studies also measured serum cortisol and both saw it fall, which is the closest thing to a mechanism the human literature offers — a stress-axis effect you can see in a blood draw, at a dose that was written down before the study started.
Extract is not the same word as root
The trials above used concentrated root extracts, not raw ground root. That one distinction does most of the damage on supplement labels. A panel reading "ashwagandha root 1,000mg" is describing a different material from "600mg of root extract," and the larger number is the less concentrated one. So when you're comparing two bottles, the question is never which milligram figure is bigger. It's whether the milligrams are of the same kind of thing the trial used, and whether the label tells you enough to know. If the amount is buried inside a proprietary blend, it doesn't, and you cannot work out which study — if any — that product is standing on.
On practicalities: both dose-anchored trials split the daily amount across two doses rather than giving it all at once, and both ran eight weeks or longer before measuring anything. That is your trial length. Perceived stress is a noisy thing to self-assess, so judge it at eight weeks against how you felt at the start — not against yesterday, which tells you about yesterday.
The caveat we'd rather you heard from us
Ashwagandha can influence thyroid hormone levels. Thyroid conditions are several times more common in women, so this is a real consideration rather than boilerplate. If you take levothyroxine or have a diagnosed thyroid condition, clear it with your doctor first.
There is a second caveat, and it is the reason we will not describe this herb as harmless. Björnsson and colleagues published a case series in Liver International in 2020 describing five patients — three identified in Iceland, two through the US Drug-Induced Liver Injury Network — who developed liver injury attributed to ashwagandha-containing supplements. All five developed jaundice, after a latency of two to twelve weeks, with a cholestatic or mixed pattern of injury. Five documented cases is genuinely rare set against how many people take this herb. Rare is not the same as impossible, and two to twelve weeks is exactly the window in which someone would otherwise assume a supplement had proven itself safe. If you develop jaundice, dark urine, persistent nausea or unexplained itching while taking it, stop and see a doctor. If you're pregnant, trying to be, or already on prescription medication, this is a conversation to have before you buy rather than after.
Good questions
How much ashwagandha should I actually take?
600mg a day of root extract, split into two 300mg doses, is the dose the research used. The 2012 trial ran that protocol for 60 days in 64 adults with a history of chronic stress and reported reduced stress and anxiety scores alongside reduced serum cortisol. Both dose-anchored trials split the daily amount rather than giving it all at once.
Is a 150mg ashwagandha capsule doing anything?
Nobody has tested it, so nobody can tell you. The lowest dose ever compared against placebo was 250mg a day, and it did beat placebo on perceived stress and cortisol, just far less decisively than 600mg. A 150mg capsule is not a smaller version of the trial; it is a different intervention with no data behind it.
When should I expect to notice anything from ashwagandha?
Eight weeks at minimum. Both dose-anchored trials ran eight weeks or longer before measuring anything, and the most-cited study ran 60 days. Perceived stress is a noisy thing to self-assess, so judge it at eight weeks against how you felt at the start, rather than against yesterday. Yesterday only tells you about yesterday.
Can ashwagandha damage your liver?
It is rare and it is documented. A 2020 case series described five patients, three identified in Iceland and two through the US Drug-Induced Liver Injury Network, who developed jaundice and liver injury attributed to ashwagandha-containing supplements, with a latency of two to twelve weeks. Stop and see a doctor if you develop jaundice, dark urine, persistent nausea or unexplained itching.
Can I take ashwagandha with thyroid medication?
Clear it with your doctor first. Ashwagandha can influence thyroid hormone levels, and thyroid conditions are several times more common in women, so this is a real consideration rather than boilerplate. The same applies if you are pregnant, trying to be, or taking any prescription medication. That is a conversation to have before you buy, not after.
Sources
- Chandrasekhar K, Kapoor J, Anishetty S. A prospective, randomized double-blind, placebo-controlled study of a high-concentration full-spectrum extract of ashwagandha root. Indian J Psychol Med, 2012. View study
- Lopresti AL, et al. An investigation into the stress-relieving and pharmacological actions of an ashwagandha extract. 2019. View study
- A standardized Ashwagandha root extract alleviates stress and anxiety by modulating stress hormones. 2023. View study
- Salve J, Pate S, Debnath K, Langade D. Adaptogenic and Anxiolytic Effects of Ashwagandha Root Extract in Healthy Adults: A Double-blind, Randomized, Placebo-controlled Clinical Study. Cureus, 2019. View study
- Björnsson HK, et al. Ashwagandha-induced liver injury: A case series from Iceland and the US Drug-Induced Liver Injury Network. Liver Int, 2020. View study
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
