Hibiscus
The Essentials

Several human trials show a small, real drop in blood pressure with two to three cups daily.
The part used is the calyx.
It can lower blood pressure further alongside medication — tell your doctor if you drink it daily.
Very few pleasant drinks come with real trial evidence. Hibiscus does. The effect is modest — a few points, not a cure — but researchers have measured it in people and repeated it across studies. And it comes in a drink you may happily choose anyway. That combination is rare and worth respecting.
What Else to Know
Blood pressure often creeps upward with age, and small measures can add up. A few points from a daily drink, a few from walking, and a few from less salt can together make a real difference to stroke risk. Hibiscus is the pleasant one on that list, and because it's caffeine-free, it doesn't cost you sleep.
Modest, trial-supported reduction in blood pressure.
Rich in anthocyanin (the natural colour pigments that make fruit red, purple or blue) antioxidants.
Cooling and thirst-quenching in hot weather.