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Hibiscus sabdariffa

Hibiscus Sabdariffa (Roselle or Sour Tea) is a tea where the usually dark colored flowers are used to brew. It appears to inhibit carbohydrate absorption to a degree and appears to be effective in reducing blood pressure.

Our evidence-based analysis on hibiscus sabdariffa features 61 unique references to scientific papers.

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Summary of Hibiscus sabdariffa

Primary information, health benefits, side effects, usage, and other important details

Hibiscus Sabdariffa (Roselle) is a supplemental herb that is derived from the plant's calyces, which are the collection of sepals separating the blooming flower from the stem. The calyces have traditionally been steeped into tea where the anthocyanins (red-blue pigmentation) is steeped into the water and drank for medicinal purposes.

Although it has a variety of claims medicinally, it appears to have evidence to support its role in reducing blood pressure in persons with elevated blood pressure. It may be this through ACE inhibitory potential (although this is admittedly weak) or benefitting the endothelium via nitric oxide related mechanisms (appears to be in better accordance with the amount of anthocyanins that reach the blood). Reductions in both diastolic and systolic blood pressure have been noted, and for the most part appear to be reliable in presence although not so much in magnitude of benefit (ie. blood pressure is reliably reduced, but the degree of reduction seems to vary).

In regards to diabetes and blood glucose control, Roselle appears to have limited evidence to support these claims but the evidence is so far in support. Mechanisms are not known, and the remarkable potency in animal studies seems to be markedly less in the limited human interventions looking at it. Roselle does appear to weakly inhibit carbohydrate absorption enzymes, yet is synergistic with Morus Alba (White Mulberry) in doing so; a tea made of White Mulberries and Roselle, although currently not supported in vivo, is possibly an effective carbohydrate absorption inhibitory tea.

The interactions of Roselle and weight loss are not too clear-cut, and it seems to be highly intertwined with studies on Roselle toxicity; Roselle is known to be toxic in higher doses, and weight loss more often than not precedes chronic toxicity. For studies that note weight loss without toxicity, it seems to be related to reduced food intake in rats and mice rather than direct fat burning effects.

The appetite suppressing effects seem to be fairly reliable in rats, but caution should be taken in applying these effects to humans. Aside from not being reported as a side-effect in any human study, the bioactive known as Hibiscus Acid is similarly structured to (-)-Hydroxycitric acid from Garcinia Cambogia which is known to reduce appetite in rats reliably but not humans.

Low doses of Roselle tea or supplements appear to be effective in reducing blood pressure, and may be anti-diabetic. It is unlikely that Roselle can cause weight loss independent of a reduction of appetite

The toxicity itself seems to occur in mice and rats in a similar idea as the blood pressure reducing effects in humans, as in they occur reliably although the dose required to induce toxicity and what exactly occurs seems to vary from one study to another. This may be related to the exact molecules mediating toxicity not being known right now. For the majority of toxic effects, the lowest they have occurred is 200mg/kg in rats (2.2g dried calyx for a 150lb human). Human studies have used this dose or above with no apparent side effects though. The toxicity of these doses of Roselle need to be evaluated more.

One concern that does exist is testicular toxicity, which occurs fairly reliably at 200mg/kg or above in animals but has not been investigated in humans. Roselle appears to be anti-fertility in men, inducing abnormal sperm morphology. In females, there was a series of studies suggesting Roselle could cause abnormal (higher) birth weights in offspring with a delay of pubertal onset; for the most part these are attributed to the appetite suppressing effect causing maternal malnutrition, with no per se mechanisms harming the pup (via lactation) currently known.

Although these toxic effects can possibly be avoided by adhering to proper dosing, the amount of safety information in humans is not as expansive as would be desired; the therapeutic threshold (degree of 'safety buffer' between the active dose and toxic dose) is also lower than desirable, so possible toxic effects with overdosing Roselle is probably more relevant than other supplements.

Higher doses of Roselle do exert toxic effects, although none of these toxic effects have been reported in humans (that being said, they have not conclusively been disproven either). It would be prudent to avoid taking too much Roselle, especially since many benefits of Roselle (elaborating on in complete summary) are not dose-dependent above the lowest observable toxic dose of 2.2g/150lb human

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How to Take

Recommended dosage, active amounts, other details

When using Hibiscus Sabdariffa as a tea, a dried calyx (the part of the blooming top of a flower that is not the petals, but beneath them) weighing about a gram is steeped into tea; drunk either once in the morning or twice a day with 8 hours between doses.

Supplemental Hibiscus Sabdariffa is taken according to the content of anthocyanins; 10mg of anthocyanins derived from Hibiscus Sabradiffa (which would be 1g of a 1% extract or 500mg of a 2% extract) appears to be effective.

Higher doses are associated with toxicity in rats, and it would be prudent to not exceed the above doses unnecessarily.

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Human Effect Matrix

Unlocked for Examine members

The Human Effect Matrix summarizes human studies to tell you what effects Hibiscus sabdariffa has on your body, how much evidence there is, and how strong these effects are.

Full details are available to Examine members.
Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Outcome Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
grade-b Notable Very High See all 6 studies
The decrease in blood pressure seen with roselle tea and supplements is notable and is greater than that seen with other supplements
grade-c Notable Moderate See all 4 studies
Mixed effects on triglycerides, but the lone study that noted a decrease noted comparable potency to pravastatin; requires more literature
grade-c - Very High See 2 studies
No significant alterations in blood glucose noted
grade-c - Very High See all 3 studies
HDL cholesterol appears to be unaffected following roselle ingestion
grade-c - Very High See all 3 studies
LDL cholesterol appears to be unaffected following Roselle ingestion
grade-c - Very High See all 3 studies
No significant changes in total cholesterol noted
grade-c - Very High See 2 studies
Weight appears to be unaffected following ingestion of Roselle tea
grade-d Minor - See study
Appears to reduce oxidative biomarkers in the body, surprisingly not the potency one would expect from in vitro evidence
grade-d Minor - See study
Possible decreases in MCP-1 with mixed or no influence on other inflammatory cytokines
grade-d Minor - See study
Has been noted to reduce lipid peroxidation
grade-d Minor - See study
A decrease in liver enzymes has been reported
grade-d - - See study
No significant influence on apolipoprotein A levels in serum
grade-d - - See study
No significant influence on Apolipoprotein B levels in serum
grade-d - - See study
No significant influence on creatinine
grade-d - - See study
No significant influence on urea
grade-d - - See study
Does not appear to influence uric acid concentrations in serum

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Things to Note

Is a Form Of

Primary Function:

Also Known As

Roselle, Isakpa, Krachiap daeng, Sour Tea

Do Not Confuse With

Hibiscus Macranthus (same genera, different species), Rosmarinic Acid, Rosa damascena

Goes Well With

  • Morus Alba in inhibiting alpha-amylase

  • Chrysanthemum Indicus in inhibiting alpha-amylase

  • Aegle marmelos in inhibiting alpha-amylase

Caution Notice

  • Higher doses of Hibiscus Sabdariffa appear to be related to toxicity, with the lowest dose exerting chronic toxicity in mice being equivalent to a human dose of 6g of the calyx per day. It would be prudent to adhere to the dosing information strictly

  • There is possible testicular toxicity associated with doses of Hibiscus Sabdariffa which are practically relevant. These have been neither refuted nor demonstrated in humans, and should at least be noted

  • Anthocyanins are heat sensitive, and if preparing Roselle tea measures should be taken to not expose the tea to excessive levels of heat and steeping. Steeping the tea does not abolish the benefits if done normally

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