Malvaceae
Hibiscus sabdariffa
Roselle · Hibiscus · Karkade · Sorrel
- Part used
- flowerfruit
- Native range
- West Africa; cultivated across the tropics
- Morphology
- An annual shrub to two and a half metres with lobed leaves and pale yellow flowers, whose fleshy deep-red calyces swell after flowering and are the part harvested.
What is in it
Evidence
Among the better-supported entries. Multiple randomised trials and meta-analyses show a modest but consistent reduction in systolic and diastolic blood pressure, with effect sizes smaller than antihypertensive drugs and comparable to some dietary interventions.
Safety
A food and generally well tolerated. Because the blood pressure effect is real, it is additive with antihypertensive treatment. Reduces levels of some drugs. Traditionally avoided in pregnancy.
Interactions: Additive with antihypertensives; Reduces plasma levels of hydrochlorothiazide and of chloroquine
Regulatory: Permitted as a food and as a listed medicine ingredient.
Historical use
Drunk as a cold or hot infusion across west and north Africa, Egypt, the Caribbean and Mexico — karkade, bissap, agua de Jamaica. Used for blood pressure and as a cooling drink.
Recorded as history and attributed where possible. Long use establishes that a plant was widely used, not that it worked, and not that it was safe.
Worth knowing
Roselle is one of the few plants in this collection where a large body of ordinary daily use and a respectable trial literature agree, and the finding is modest and useful rather than dramatic.
It also demonstrates the point that a real effect creates a real interaction. Because hibiscus genuinely lowers blood pressure, someone already on antihypertensive medication who starts drinking it daily is adding to their treatment without anyone recording it — and it separately reduces blood levels of hydrochlorothiazide, a common antihypertensive, which pushes in the other direction.
An inert tea cannot do either of those things. This is what it looks like when a herb works.
Nomenclature verified against GBIF backbone taxonomy.