Hibiscus (Hibiscus sabdariffa, Malvaceae), commonly known as jamaica or flor de jamaica in Mexico and roselle in Europe, is used as a flavoring and coloring agent in various herbal beverages, and also as a traditional medicine, particularly in Africa. The part used is the calyx, the outermost part of the flower formed by the sepals. Hibiscus first gained popularity in the United States as a primary flavor of one of America’s first popular herbal teas in the 1970s—Celestial Seasonings’ breakthrough “Red Zinger,” which derived its characteristic color from the dark red wine-colored calyces.

The primary active constituents in hibiscus calyces are anthocyanins, which have antioxidative, antitumor, and anticarcinogenic activity. Studies indicate that hibiscus preparations have shown activity on the cardiovascular system. Hibiscus has been shown to have a natriuretic effect (eliminates extra sodium) and can inhibit angiotensin-converting enzyme (ACE), which causes an elevation of blood pressure. The purpose of this study was to evaluate the efficacy and safety of an herbal medicinal product prepared from hibiscus extract and to compare it with lisinopril, an ACE inhibitor used to treat hypertension. A previously published smaller clinical trial by this Mexican group had indicated a hypotensive effect of hibiscus extract.¹

Outpatients (n=193) of the Regional General Hospital No. 1 (HGR 1) of the Mexican Institute of Social Security (IMSS) in Cuernavaca, Morelos, Mexico with stage 1 or 2 hypertension participated in this randomized, reference-controlled, double-blind study. Patients received either lisinopril 10 mg/day or hibiscus dried calyx extract standardized to 250 mg of total anthocyanins per day for 4 weeks. The authors performed the extraction of this material.

Blood pressure and urine samples were monitored. At baseline, there were no significant differences in blood pressure between groups. Both treatments reduced blood pressure, but the effects were not immediately evident. After 4 weeks of treatment, the hibiscus extract lowered the systolic blood pressure by 11.58% and diastolic blood pressure by 12.21%. Lisinopril had a greater effect, lowering systolic blood pressure by 15.79% and diastolic blood pressure by 15.68%. Both treatments were well tolerated. Two cases of nervousness were reported in the hibiscus extract–treated patients, but this effect is not consistent with known use of hibiscus, so it is probable that these cases were probably idiopathic (i.e., of unknown cause or origin). Patients treated with hibiscus extract had a significant increase in serum chloride, a decrease in plasma sodium, and no effect on the potassium level. In contrast, lisinopril caused only a significant decrease in plasma chloride levels. The ACE inhibitory effect was significantly higher in the lisinopril-treated patients (P < 00.004).