A new clinical study published in Current Therapeutic Research identified withanolide glycosides as the key drivers of bioavailability in ashwagandha (Withania somnifera) extracts.

This marks the first direct evidence in humans that the type of withanolide — not just the total content — influences absorption and efficacy, according to Arjuna Natural Pvt., Ltd., whose Shoden ashwagandha extract demonstrated superior performance in uptake in the study subjects.

The randomized, open-label, crossover clinical study, led by Priyank Rathi, MD, evaluated the bioavailability in 16 healthy human volunteers of four commercially available, standardized ashwagandha extracts with varying compositions, including: Shoden standardized to 35% Withania somnifera withanolide glycosides (WS-35), 10% (WS-10), 5% (WS-5), or 2.5% (WS-2.5).

Each sample was standardized to deliver 185 mg of total withanolides. Seventeen blood samples were collected over a 24-hour period after dosing. Plasma concentrations of withanolide A, withanoside IV, withaferin A, and total withanolides were quantified, and pharmacokinetic parameters were calculated.

Results showed extracts rich in withanolide glycosides — particularly those derived from the plant — demonstrated higher systemic exposure. With Shoden in the lead, these extracts showed longer half-lives, indicating prolonged circulation of active compounds in the body.

“Clinical data now confirm that withanolide glycosides stand out not just for quantity but for quality, with higher bioavailable than other withanolide types,” said Benny Antony, PhD, joint managing director of Arjuna Natural. “Our findings suggest that the strength of ashwagandha is in its withanolide profile, specifically the chemical nature of the withanolides — and not their total amount. This plays a critical role in determining the uptake and metabolism of ashwagandha extracts in the body for optimal effect. This study emphasized the importance of extract composition and the plant parts used.”

“These findings have major implications for both consumers and supplement manufacturers,” he added. “As ashwagandha continues to gain popularity for its adaptogenic, cognitive, and stress-relieving benefits, the current research underscores the need for more detailed labeling and standardization that goes beyond total withanolide content. Future clinical studies and product formulations should consider the specific withanolide profile — particularly the presence of glycosides — to deliver ashwagandha extracts with maximum efficacy and consistency.”