Anxiety disorders are among the leading causes of health burden worldwide, affecting an estimated 4% of the global population(1, 2). These disorders are the most prevalent mental health conditions worldwide and impose substantial disability and economic costs. Although several treatments are available, including psychological interventions (cognitive behavioural therapy), and pharmacological treatments (medications), their use is limited by access barriers and stigma(2). Additionally, anti-anxiety medications may cause adverse effects and can be associated with long-term health risks. There is an increasing interest in the use of nutraceuticals derived from plant food products as approaches to prevent or delay disease onset or support the management of chronic conditions, including mental disorders. This study aims to investigate the effects of green rooibos (Aspalathus linearis) extract supplementation on anxiety levels in adults living with mild-to-moderate anxiety. The trial was approved by the University of Canberra Human Research Ethics Committee (UC HREC 13602) and registered with the Australian New Zealand Clinical Trials Registry (ACTRN12624000373572; Universal Trial Number U1111-1301-6151. This double-blind, placebo-controlled, parallel, randomised controlled trial enrolled 60 adults aged 18-65 years with mild-to-moderate anxiety. Participants received either green rooibos tea extract (19.25 mg aspalathin per capsule; n = 30) or placebo (n = 30) over an 8-week intervention, taking one capsule each morning during the first week and two capsules each morning during the subsequent 7 weeks. Recruitment and the intervention period have now been completed; data analysis is ongoing. The anxiety subscale of the 21-item Depression, Anxiety and Stress Scale was the primary outcome, assessed from baseline to post-intervention. Secondary outcomes included salivary biomarkers (cortisol, α-amylase), heart rate variability, sleep quality, physical activity and dietary intake. Measurements were collected at baseline, mid-intervention, and post-intervention. The findings may help determine whether green rooibos extract supplementation is associated with reduced anxiety and improvements in related health markers in adults with mild-to-moderate anxiety. The findings may also provide insight into physiological pathways relevant to nutraceutical interventions for anxiety. If clinically relevant effects are observed, green rooibos extract could represent an accessible and well-tolerated adjunct to current anxiety management strategies.