A review and update on the use of Hibiscus sabdariffa (karkadeh) in the treatment of essential hypertension

Background
Essential hypertension is a common, significant worldwide disease whose adequate treatment requires a multidrug regime in 70% of patients, where adherence to treatment ranges from low to very low (72.7% to 19.7%), and where each additional medication used causes a decrease in adherence by up to 85%. Hibiscus sabdariffa L. (HS) is a widely used herb which has been used for its antihypertensive effect, which may offer to play a useful synergistic role to pharmacotherapy.

Objectives
This review sought to identify relevant basic laboratory studies, human randomised controlled studies (RCTs), meta-analysis and reviews studying the safety, mechanism and/or effect of HS on blood pressure.

Material and methods
A search was done, ending on the 1st of October 2019, of the following databases: Medline, COCHRANE and EMBASE. RCTs were assessed for quality using the Jadad scale.

Results
Basic laboratory studies have shown that HS is rich in bioactive anthocyanins, which inhibit angiotensin-converting enzyme (ACE) in a dose-dependent manner, and HS extracts also have a direct vasodilator effect. 13 safety studies have found HS to be safe at normal doses with minimal clinically important drug-herb interaction. Very high doses (> 300 mg/kg/day) are associated with liver enzyme abnormalities and raised uric acid in rat studies. 14 RCTs show that HS causes a significant reduction in systolic blood pressure (-6.3 to -31.9 mm Hg) and diastolic blood pressure (-1.1 to -19.7 mm Hg).

Conclusions
HS is a widely available, acceptable, cheap and effective synergistic agent in the management of essential hypertension.