23/05/2026
A pilot clinical study evaluated a traditional dried rosemary leaf (Rosmarinus officinalis) infusion in untreated grade 1 hypertensive patients (defined as systolic BP 140 to 159 mmHg and/or diastolic BP 90 to 99 mmHg) using a pragmatic but loosely controlled design. Over 45 days, participants consumed a daily tea made from 2 g powdered rosemary leaf infused in 100 mL hot water for 15 minutes, delivering approximately 38 mg polyphenols including 18 mg of rosmarinic acid. The use of powdered leaf is noteworthy, as it substantially increases extraction yield compared with intact leaf.
In the hypertensive group (n=30 completers), the herbal intervention produced statistically significant reductions in ambulatory blood pressure, including −6.3 mmHg systolic and −4.9 mmHg diastolic (24-hour averages). These translate to moderate within-subject effect sizes (0.5 to 0.65), suggesting a potentially meaningful clinical effect. There was no impact in a smaller group of normotensive participants, no change in nocturnal BP, and no effect on pulse pressure or heart rate. While these effect sizes are clinically relevant for early hypertension, interpretation is limited by the absence of a randomised placebo-controlled design, meaning regression to the mean and behavioural factors cannot be excluded.
Methodologically, the study’s main strength is the use of 24-hour ambulatory BP monitoring, which improves reliability over clinic readings, along with phytochemical characterisation of the intervention. However, it is constrained by a small sample size and lack of blinding and a proper control group. Safety signals were reassuring over the 45 days, with no adverse events and stable biochemistry. Clinically, this study should be viewed as hypothesis-generating: it suggests rosemary infusion may exert modest antihypertensive effects, but requires confirmation in well-powered, randomised, dose-ranging trials before integration into standard care.
Beyond blood pressure, rosemary tea shows a range of emerging clinical effects, particularly in the neurocognitive space. Small human studies suggest improvements in mood, anxiety, and cognitive performance, and notably, a pilot trial has reported a marked increase in circulating brain-derived neurotrophic factor (BDNF) following short-term rosemary tea consumption, pointing to a potential role in neuroplasticity and stress resilience. Mechanistically, this aligns with its polyphenols (such as rosmarinic acid and carnosol) acting via Nrf2, anti-inflammatory and CREB-related pathways (cAMP response element-binding protein). Hence the dried leaf is suitable in this context (since the polyphenols are retained on drying), even though it is lower in essential oil compared to fresh rosemary.
So at this point there is no harm and possibly great benefit in the suggestion that hypertensive patients could start taking rosemary leaf tea as part of their overall regime.
For more information see: https://www.sciencedirect.com/science/article/pii/S2667031325000569?via%3Dihub
