Back to the Roots: Safety and Tolerability of Standardised Ashwagandha (Withania somnifera) Root Extract in Healthy Adults—A Systematic Review of Biomarkers and Adverse Events

Background: Standardised Ashwagandha root extract (SARE), characterised by its content of bioactive withanolides, is widely used for its antioxidant and adaptogenic properties; however, recent case reports have raised safety concerns, primarily involving non-standardised or multi-ingredient formulations. This systematic review evaluated the safety and tolerability of SARE in healthy adults, with a focus on clinical biomarkers and adverse event reporting. Methods: Randomised trials were identified through searches of PubMed, Web of Science and Google Scholar, published from 2010 to April 2026. Studies administering single-ingredient, standardised root-only extracts to generally healthy populations were included. Risk of bias was assessed using the Cochrane RoB 2 tool. Results: Twenty-three studies with a total of 2317 participants met the inclusion criteria, with doses ranging from 125 to 600 mg/day and intervention durations from a single dose to 180 days. Across studies, hepatic, renal, haematological, endocrine, and cardiovascular biomarkers remained within normal clinical ranges, with no clinically meaningful adverse alterations reported. Reductions in cortisol were consistently observed, while increases in testosterone remained within physiological ranges. No serious adverse events attributable to SARE were reported. Mild adverse events, including gastrointestinal discomfort, headache, and transient drowsiness, were infrequently reported and occurred in both intervention and comparator groups. Conclusions: SARE was well tolerated in healthy adults at the studied doses and durations. However, limited long-term data (>180 days) and heterogeneity in study design and reporting warrant further large-scale, standardised trials to confirm safety across extended use and diverse populations. The review is registered in the PROSPERO database with ID CRD420261337116.