What Clinical Studies Say About Dosage

Study amounts are not advice

This page lists amounts that were given in named trials or listed in official herbal monographs. It is not a guide to what you should take. A trial amount tells you what one extract did in one group of people over one period. A pharmacist or clinician decides what is right for a person, taking their medicines and health into account.

Before the details, three safety points. NIH says ashwagandha should be avoided during pregnancy and not used while breastfeeding. [1] NIH says ashwagandha may interact with medicines for diabetes and high blood pressure, immunosuppressants, sedatives, anti-seizure medicines and thyroid hormone medicines. [1] Tell your surgical team about any supplement. See How Interactions Work.

What the sources say about "the right amount"

A 2026 systematic review of 22 ashwagandha trials found a link between amount and stress scores, but its authors say better trials are still needed to establish the most effective dosages and durations. [2] A review of rhodiola trials in healthy adults reported that unclear results likely stem from variable dosing and inconsistent durations. [3] In plain terms, the research does not yet show a best amount.

Amounts used in trials (human studies)

Strength of evidence is our label for the whole row: small single trials are "promising but limited" at best.

Trial funding is not stated in the abstracts we read, so we cannot say who paid for these studies.

Official monograph amounts (traditional use)

The European Medicines Agency's herbal committee (HMPC) publishes monographs for traditional herbal medicines. They are based on long use, not on proof of benefit. The monograph states that these products are for use "exclusively based upon long-standing use". [10] They apply to registered products, not to every supplement.

For astragalus, NIH says taking up to 60 grams per day for as long as 4 months does not seem to cause adverse effects, but that a thorough safety evaluation has not been done. [13] That is a safety statement about what was observed, not a recommended amount. We found no European monograph amount for ashwagandha in the sources we read.

Plant names above were checked against GBIF. [14][15]

Why "milligrams on the label" cannot be compared

Two ashwagandha extracts can contain the same total withanolides yet reach very different blood levels. In a 16-person crossover study under fasting conditions, four extracts were each standardized to deliver 185 mg of total withanolides, and the one rich in withanolide glycosides had significantly higher bioavailability. [16] It was a single dose in healthy adults, so it shows that extract type matters, not what to take. See Standardized Extracts, Extract Ratios and Root vs Leaf Ashwagandha.

Limits

Most trials above are small and short. A systematic review of rhodiola trials noted a lack of independent replication of the single studies. [17] NIH describes the rhodiola evidence as not enough to say whether it is useful for any health purpose. [18]