Adaptogenic and anxiolytic effects of ashwagandha root extract in healthy adults: A double-blind, randomized, placebo-controlled clinical Study. 

This 2019, eight week randomised double-blind placebo controlled study of 58 participants examined the dose dependent effects of aqueous ashwagandha root extract on otherwise healthy participants facing stress and anxiety. The 300 mg group had the most pronounced decrease in Perceived Stress Scale (PSS) scores from baseline. 

References:

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;11(12):e6466. Published 2019 Dec 25. doi:10.7759/cureus.6466