Randomized, Double-Blind, Crossover Study Comparing the Bioavailability of 4 Ashwagandha (Withania somnifera (L.)...

Withania somnifera (L.) Dunal, commonly known as ashwagandha, is a well-known plant in ayurvedic medicine, widely valued for its therapeutic potential. Although numerous clinical studies have explored its diverse health benefits, limited data are available on the pharmacokinetic (PK) properties and comparative bioavailability of its key bioactive constituents in humans.

This study aimed to evaluate and compare the oral bioavailability of 4 commercially standardized ashwagandha extracts under fasting conditions in healthy adults.

This randomized, double-blind, 4-treatment, 4-period, 4-sequence, single dose, 4-way crossover study was conducted in 16 healthy human volunteers. Participants received a single oral dose of 1 of 4 ashwagandha extracts, with varying compositions of 35% (Withania somnifera [WS]-35) or 10% (WS-10) withanolide glycosides, or 5% (WS-5) or 2.5% (WS-2.5) withanolides, each standardized to deliver 185 mg of total withanolides. Seventeen blood samples were collected over a 24-hour period after dose administration. Plasma concentrations of withanolide A, withanoside IV, withaferin A, and total withanolides were quantified, and PK parameters were calculated.

Withania somnifera-35 had significantly superior bioavailability compared with the other extracts. The AUC_0-t for total withanolides per gram of WS-35 was 118.28, 226.11, and 267.83 times better than WS-10, WS-5, and WS-2.5 respectively. Withania somnifera-35 exhibited a significantly higher C_max, longer half-life, extended mean residence time, and lower systemic clearance, attributable to its higher withanolide glycoside content.

These findings emphasize the critical role of withanolide glycosides in determining the PK performance of ashwagandha supplements. The enhanced bioavailability of WS-35 supports its preferential use in therapeutic applications and provides a strong rationale for further investigation into dose-response relationships and the long-term efficacy of standardized, high-bioavailability formulations. Clinical Trial Registry of India identifier: CTRI/2020/10/028397.