Red tea (Roselle) for lowering blood pressure in adults

Key messages:

We don't know if taking Roselle lowers blood pressure in people with hypertension (high blood pressure).

We don’t know if Roselle is safe for people with hypertension to consume or if it affects heart rate or pulse pressure.

What did we want to find out?

We wanted to know if red tea (Roselle) is a safe and effective treatment for lowering blood pressure in adults with high blood pressure when compared to placebo (dummy treatment) or no treatment. Roselle contains substances known as anthocyanins which have been shown to have lowered blood pressure in studies carried out in animals and humans.

What did we do?

We searched for studies that compared Roselle to placebo or no treatment in people with hypertension.  

What did we find?

We included one study with 60 participants with type 2 diabetes and hypertension. Participants consumed either a capsule of pure Roselle extract or a placebo containing lactose for eight weeks. We are not sure if Roselle has an effect on blood pressure and the study did not report on the safety of Roselle or on changes to heart rate.

What are the main limitations of the evidence?

We found only one trial which included a small number of participants, all of whom had diabetes. More studies with various types of participants and different ways of taking Roselle (forms, amounts, and time of day, length of use) are needed.

How up to date is the evidence?

The review updates our previous review. We searched for randomised controlled trials (studies in which participants are randomly assigned to one of two or more treatment groups) in core databases up to August 2021, and searched local and regional Chinese and Thai databases by hand up to October 2020.

Authors' conclusions: 

The evidence is currently insufficient to determine the effectiveness of Roselle compared to placebo for controlling or lowering blood pressure in people with hypertension. The certainty of evidence was very low due to methodological limitations, imprecision, and indirectness. There is a need for rigorous RCTs that address the review question.

Read the full abstract...

Hypertension is considered to be a serious health problem worldwide. Controlling and lowering blood pressure are of significant benefit to people with hypertension because hypertension is a risk factor for stroke, heart disease, and cardiovascular disease. Roselle, the tropical plant Hibiscus sabdariffa, also commonly called sour tea or red tea, has been used as both a thirst-quenching drink and for medicinal purposes.


To assess the effect of Roselle on blood pressure in people with primary hypertension.

Search strategy: 

For this update, the Cochrane Hypertension Information Specialist searched the following databases and trials registers for randomised controlled trials (RCTs): the Cochrane Hypertension Specialised Register (to 6 August 2021), Cochrane Central Register of Controlled Trials (CENTRAL; 2021, Issue 7), MEDLINE Ovid (1946 to 5 August 2021), Embase Ovid (1974 to 5 August 2021), ProQuest Dissertations & Theses (to 6 August 2021), Web of Science Clarivate (to 7 August 2021), Food Science and Technology Abstracts Clarivate (to 7 August 2021), the WHO International Clinical Trials Registry Platform (to 6 August 2021), and the US National Institutes of Health Ongoing Trials Register (to 6 August 2021). We searched Google Scholar and OpenSIGLE. We also handsearched local and regional Chinese databases: CBM, CMCC, TCMLARS, CNKI, CMAC, and the Index to Chinese Periodical Literature (to 14 September 2020), as well as Thai databases (ThaiJO, CUIR, TDC, CMU e-Theses, TCTR) (to 3 October 2020). There were no language or publication date restrictions.

Selection criteria: 

We sought RCTs evaluating the use of any forms of Roselle with placebo or no treatment in adults with hypertension. Our primary outcome was change in trough and/or peak systolic and diastolic blood pressure (SBP, DBP). Secondary outcomes were withdrawals due to adverse effects, change in pulse pressure, and change in heart rate.

Data collection and analysis: 

All search results were managed using Covidence and re-checked for the number of records, inclusion and exclusion of studies with Mendeley reference management software. We used standard methodological procedures expected by Cochrane. Two review authors worked independently in parallel for screening (titles and abstracts, and full reports), data extraction, risk of bias assessment, and assessment of the certainty of the evidence using the GRADE approach. Any disagreements were resolved by discussion or by consultation with the third review author if necessary. We presented mean difference (MD) of change in SBP and DBP with their corresponding 95% confidence interval (CI).

Main results: 

For this update, only one RCT with a parallel-group design involving 60 participants with type 2 diabetes mellitus fulfilled the inclusion criteria. This study investigated the effect of Roselle extract capsules (total dose of 5600 mg) compared with placebo (lactose) at eight weeks. The study was at low risk of selection bias, performance bias, and detection bias. Conversely, it was at high risk of attrition bias, reporting bias, and other bias (baseline imbalance).

We have very little confidence in the effect estimate of Roselle on change-from-baseline in both SBP and DBP between the two groups. The MD of change in SBP was 1.65, 95% CI −7.89 to 11.19 mmHg, 52 participants, very low-certainty evidence. The MD of change in DBP was 4.60, 95% CI −1.38 to 10.58 mmHg, 52 participants, very low-certainty evidence. Our secondary outcomes of withdrawals due to adverse effects, change in pulse pressure, and change in heart rate were not reported. Due to the limited available data, no secondary analyses were performed (subgroup and sensitivity analysis).