Which Tea Lowers Blood Pressure? Hibiscus & More

Tea is one of the world's most popular drinks, and several kinds have been tested for their effects on blood pressure. The honest summary: hibiscus has the best evidence, green and black tea have small effects, most herbal teas have barely been studied — and licorice tea can actually raise your blood pressure.

Hibiscus tea: the best evidence

Hibiscus tea (also called sour tea, sorrel, karkadé or flor de Jamaica) is made from the deep red calyces of Hibiscus sabdariffa. It is rich in anthocyanins and other polyphenols that may relax blood vessels and have a mild diuretic effect.

Several small randomized trials, many lasting four to six weeks, found that two to three cups a day lowered systolic blood pressure by around 5–7 mmHg in people with mild hypertension or high-normal blood pressure. A few studies even compared it favorably with low-dose medication. However, most trials were small, short and of varying quality, so the true effect is probably modest.

Cautions:

• It may add to the effect of blood pressure drugs, especially diuretics — keep measuring and tell your doctor.
• Hibiscus may interact with some medications, including hydrochlorothiazide, the antimalarial chloroquine and possibly acetaminophen (paracetamol) metabolism.
• Avoid it during pregnancy and breastfeeding; safety has not been established.
• It may lower blood sugar slightly — relevant if you take antidiabetic drugs.

Green and black tea: small effects

Both come from the same plant, Camellia sinensis. Green tea contains more catechins, black tea more theaflavins. Meta-analyses of controlled trials show that regular drinking over at least 12 weeks lowers blood pressure by roughly 2 mmHg systolic and 1 mmHg diastolic. That is small for an individual, but large population studies also link regular tea drinking to a lower risk of stroke and heart disease.

Very high doses of green tea extract in capsules have been linked to rare cases of liver injury, and green tea can reduce the absorption of the beta blocker nadolol. Drinking the tea itself in normal amounts is considered safe for most people.

Chamomile, rooibos and other herbal teas

Chamomile, rooibos, peppermint, lemon balm and similar infusions are pleasant, caffeine-free and may help you relax. But there is little or no good clinical evidence that they lower blood pressure. A warm, unsweetened cup can still be a good replacement for sugary drinks or alcohol. Chamomile can, in rare cases, cause allergic reactions in people sensitive to ragweed and may interact with warfarin.

Avoid licorice tea — it raises blood pressure

Licorice root contains glycyrrhizin, which makes the body retain sodium and lose potassium. Regular consumption of licorice tea, licorice candy or some herbal blends can raise blood pressure significantly and lower potassium to dangerous levels. Check the ingredient list of herbal and "detox" teas for licorice (sometimes listed as Glycyrrhiza glabra or sweet root). People with hypertension, heart or kidney disease, and pregnant women should avoid it.

What about caffeine?

Caffeine can raise blood pressure by a few mmHg for a few hours, especially in people who are not used to it. Regular tea drinkers become largely tolerant to this effect. Typical caffeine content per cup (about 240 ml / 8 oz):

More on this in coffee and blood pressure. Avoid caffeine in the 30 minutes before you measure your blood pressure.

The bottom line

Unsweetened tea is a healthy drink and can make a small contribution to lower blood pressure, but it is not a substitute for treatment. Herbal products are not regulated like medicines, and their strength varies. Never stop or reduce prescribed blood pressure medication in favor of tea — combine it with proven measures like less salt, more exercise and less alcohol.