Herbs and blood pressure: what the studies show

The most dangerous example is liquorice root (also known as sweet root), found in teas, cough syrups and even sweets. Its glycyrrhizic acid makes the body retain sodium and water and lose potassium, which raises blood pressure. A 2024 meta-analysis confirms that even low doses increase the values, and the WHO recommends not exceeding 100 mg of glycyrrhizic acid per day.

Ginseng can also raise blood pressure in some people and disturb sleep, so in hypertension it is not recommended without medical advice. The same applies to ephedra, banned in many countries precisely because of cardiovascular risks.

Hibiscus is the star: a meta-analysis found that regular consumption lowers systolic blood pressure by about 7 mmHg on average, with a stronger effect in people with higher values. Garlic has a more modest but also studied effect: about 4 mmHg down in hypertensive patients, while in people with normal blood pressure it barely changes it. A note: these are study data, and the treatment of high blood pressure is determined and prescribed by a doctor.

This, however, is a coin with two sides: in a hypertensive patient on therapy, hibiscus and garlic in concentrated form can amplify the medicines and lower the pressure too much. So treat them as an addition to the regimen, agreed with the doctor, not as a replacement for therapy.

First: never stop the prescribed therapy in favour of tea, even the proven hibiscus has an effect of about 7 mmHg, while values of 160 require medicines. Second: read the composition of every herbal blend and watch for liquorice. Third: measure your blood pressure regularly and if it changes after a new herb, tell your doctor.

And remember the general rule from the article I wrote about herbs: a herb is a biologically active substance. That is exactly why it helps, harms and interacts with medicines.

This article was written by Donka Arabadzhova, Master of Pharmacy, and confirmed by the following sources: the 2024 meta-analysis on the effect of glycyrrhizic acid on blood pressure, the meta-analysis on hibiscus and blood pressure (PMC, 2022) and the meta-analysis on garlic and blood pressure (Ried and colleagues).