This 2022 meta-analysis and systematic review included data from 13 randomized control trials (1205 participants) relating to the efficacy of Hibiscus sabdariffa in patients with mild-to-moderate hypertension or metabolic syndrome. Authors concluded that Hibiscus sabdariffa is effective in reducing the SBP and DBP in patients with mild-to-moderate hypertension but was not more effective in those with MetS nor superior to antihypertensive drugs.
Abdelmonem, M., Ebada, M. A., Diab, S., Ahmed, M. M., Zaazouee, M. S., Essa, T. M., ElBaz, Z. S., Ghaith, H. S., Abdella, W. S., Ebada, M., & Negida, A. (2022). Efficacy of Hibiscus sabdariffa on Reducing Blood Pressure in Patients With Mild-to-Moderate Hypertension: A Systematic Review and Meta-Analysis of Published Randomized Controlled Trials. Journal of cardiovascular pharmacology, 79(1), e64–e74. https://doi.org/10.1097/FJC.0000000000001161