Hibiscus (Hibiscus sabdariffa L.)
1. Identity
Botanical and Chemical Names
Hibiscus (Malvaceae) is a genus of herbs, shrubs, and trees whose 250 species are widely distributed in tropical and subtropical regions of the world. The species of greatest dietary supplement and medicinal significance is Hibiscus sabdariffa L., commonly known as roselle. Botanical synonyms include Sabdariffa rubra Kostel., Abelmoschus cruentus (Bertol.) Walp., Fucaria sabdariffa Ulbr., Hibiscus cruentus Bertol., H. fraternus L., and H. palmatilobus Baill.
It belongs to the family Malvaceae and is known in Arabic as karkade. English common names include roselle, sorrel, red sorrel, and sour tea. Other regional names include jamaica (Spanish), bissap, and red tea.
Botanical Description and Natural Source
Hibiscus sabdariffa is a shrubby tropical plant that produces light yellow flowers with reddish-purple centers. After the petals drop from the flower, its remaining deep red calyces (the cup-like structures formed by the sepals) grow into seed-containing pods that look like flower buds. The roselle is a plant of African origin that has been widely adopted by various cultures, especially in Latin America, the Caribbean, and some regions of Asia.
Hibiscus is now widely cultivated for its flowers, fruit, and calyces in the tropical and subtropical regions of almost every continent. Most of the hibiscus plant's economic value, particularly as an ingredient in herbal teas, comes from the red calyx, although the leaves, seeds, and flowers are also used in local forms of traditional medicine. In commerce, the calyces are known by the names hibiscus and roselle.
Common Forms and Preparations
The HS calyces are widely used for cosmetic, food, and medicinal applications. According to ethnobotanical evidence, decoction, infusion, or maceration extracts from HS calyces have been used in folk medicine to treat many ailments. Commercial preparations of hibiscus include dried whole calyces, standardized aqueous extracts in capsule or tablet form, and dried powders. A large number of products with Hibiscus sabdariffa in their composition are available in the market, sometimes accounting for up to 50% of the total ingredient, and it is frequently used as a basic constituent of herbal tea.
2. Traditional and Historical Use
Origins and Early Use in Africa
Hibiscus sabdariffa is believed to have originated in tropical regions of Africa, with evidence dating back to its use in Sudan around 4000 BC. It was initially cultivated for its edible seeds, then its foliage, young shoots, and flower parts were used for food and medicine. It became well-known for its fleshy calyces, which have been used in many regions of the world for jams, beverages, and other food items.
Hibiscus is believed to have originated in Sudan, where it appeared in traditional medicinal preparations and celebratory drinks. Through trade and cultural exchange, it spread to regions with similar tropical climates, such as Egypt, Nigeria, Myanmar, Thailand, China, and more.
Ancient Egypt
In ancient medicine, the plant's vibrant red calyces were infused into teas and other decoctions to treat sore throats and coughs while supporting kidney health, as noted in the Ebers Papyrus, an ancient medical document. A special drink known as Karkadeh, or "Tea of the Pharaohs," is believed to have been consumed by Egyptian royalty and was made from Hibiscus sabdariffa. In Egypt and Sudan, the deep red tea from the calyces, called karkade, is popular as a "refrigerant," i.e., a beverage that helps lower body temperature.
West Africa
In various African countries, H. sabdariffa is brewed into a popular drink called "Bissap." This soft drink is valued for its rich taste and health-promoting properties such as its potential to reduce body weight and improve liver health. The calyxes are regularly eaten dried or fresh and contribute a sour flavor to portions of mixed vegetables and sauces. In many communities, hibiscus flowers are served in soups or as a vegetable, highlighting their nutritional value. In Nigeria, hibiscus — or zobo — is both a daily staple and a ceremonial drink.
Latin America and the Caribbean
In Mexico and Central America, it is known as agua de Jamaica, a drink brewed with cinnamon or cloves and sweetened to taste. From West Africa to Latin America and Asia, the calyces of Hibiscus sabdariffa have been used in social rituals, daily preparations, and traditional formulas associated with well-being.
Asia
In regions such as China and Thailand, different parts of the roselle plant (including the flower, leaves, calyx, and corolla) are commonly consumed as a thirst-quenching beverage. In India and other parts of Asia, the flowers of related Hibiscus species are used in conventional medicines to treat various ailments, including inflammation and hair loss, and extracts from the flowers are used in shampoos and conditioners to promote scalp health.
Traditional Medicinal Applications
Many species belonging to this genus have been used since ancient times as folk remedies for various disorders. In Ayurveda, Hibiscus esculentus L. fruits are considered tonic, astringent, and aphrodisiac. In Unani medicine, the fruits are considered emollient and useful for treating urinary disorders. Scientific evidence has since demonstrated the pharmacological potential of roselle, including antihypertensive, anti-hyperlipidaemic, anti-inflammatory, antimicrobial, diuretic, uricosuric, and anaemia-treating effects.
3. Key Constituents and Active Compounds
Anthocyanins
Anthocyanins are the major flavonoids present in H. sabdariffa; they are responsible for its characteristic color pigment. Anthocyanins are water-soluble glycosides or acylglycosides of anthocyanidin, which are derivatives of the 2-phenylbenzopyrylium salt. Delphinidin 3-sambubioside forms about 85% of the anthocyanin content of H. sabdariffa, including cyanidin 3-sambubioside (major pigment), and delphinidin-3-glucoside and cyanidin 3-glucoside as minor pigments.
Among four anthocyanins in the calyx, delphinidin 3-sambubioside and cyanidin 3-sambubioside are the major anthocyanins, with lesser amounts of delphinidin 3-glucoside and cyanidin 3-glucoside. The red accession PI 275414 had the highest concentration of total anthocyanins (32.7 mg·g⁻¹ dry weight).
Phenolic Acids
The predominant phenolic acids in extracts from H. sabdariffa include protocatechuic acid (PCA), 3-O-caffeoylquinic acid, chlorogenic acid, neochlorogenic acid, methyl digallate, methyl chlorogenate, coumaroylquinic acid, dihydroferulic acid 4-O-glucuronide, 5-O-caffeoylshikimic acid, and ethyl chlorogenate.
Chlorogenic acid concentrations were higher in calyces (13.1 to 25.4 mg·g⁻¹) than in leaves (0.7 to 2.0 mg·g⁻¹).
Flavonoids
The aglycones and O- and 3-substituted derivatives of quercetin, myricetin, kaempferol, gossypetin, and methyl epigallocatechin have also been identified from extracts of H. sabdariffa. Additional flavonoids include hibiscetin-3-glucoside (hibiscitrin), gossypitrin (7-glucoside of gossypetin), gossytrin, sabdaritrin, and quercetin and its glycoside, as well as luteolin.
Organic Acids
The calyx is rich in organic acids including citric, hydroxycitric, malic, tartaric, and hibiscus (hibiscic) acids.
Other Constituents
Numerous publications indicate that roselle calyces and other parts of the plant are rich in polyphenols (anthocyanins, flavonoids, phenolic acids, tannins), polysaccharides, pectins, non-phenolic organic acids, and carotenoids. Mucilage polysaccharides are also present.
The white and rose roselle variants differ in content of active compounds, but only to a slight extent; the red variety is characterized by a higher content of total phenols, flavonoids, and anthocyanins than the white variety. The white variety is characterized by a higher ability to scavenge free radicals than the red variety.
Mechanisms of Action
Possible mechanisms underlying the pharmacological effects of hibiscus include the strong antioxidant activities of anthocyanins and phenolic acids, the inhibition of pancreatic α-amylase and intestinal α-glucosidase enzymes by organic acids, the inhibition of angiotensin I converting enzyme (ACE) by flavones, the vaso-relaxant effects of anthocyanins and/or flavonoids, as well as the hypocholesterolemic action of pectins.
Among the compounds identified, delphinidin 3-sambubioside and cyanidin 3-sambubioside have been shown to inhibit angiotensin-converting enzyme, while quercetin has been shown to exert vasodilator activity. Some studies propose that the blood pressure effects are due to improved vasodilation through inhibiting calcium influx into vascular smooth muscle cells, or by acting as a diuretic through increased excretion of sodium and chloride and increased kidney filtration.
The calyx extract has been shown to inhibit enzymes cyclooxygenase COX-1 and COX-2, and also to downregulate the expression of COX-2 in lipopolysaccharide-treated cells, suggesting its anti-inflammatory activity.
Quercetin present in Hibiscus sabdariffa has an effect on the vascular endothelium causing nitric oxide release and increasing renal vasorelaxation by increasing kidney filtration. Therefore, the diuretic effect of Hibiscus sabdariffa may be mediated by nitric oxide release.
Several mechanisms have been proposed to explain cholesterol- and lipid-modulating properties of hibiscus, such as inhibition of HMG-CoA reductase or inhibition of triacylglycerol production by hibiscus acid racemization.
4. Scientific Evidence by Health Area
4.1 Blood Pressure and Hypertension
Blood pressure is the most extensively studied area for hibiscus supplementation in humans. Evidence comes from multiple randomized controlled trials (RCTs) and systematic reviews.
Overall, hibiscus exerts stronger blood pressure-lowering effects in individuals who have higher blood pressure at baseline. A meta-analysis indicated that hibiscus significantly lowered systolic blood pressure (SBP) (−7.92% from baseline) and showed a nonsignificant trend to lower diastolic blood pressure (DBP) (−6.84% from baseline).
A further meta-analysis found hibiscus exerted stronger effects on systolic BP (−7.10 mmHg [95% CI, −13.00, −1.20]; I² = 95%; P = 0.02) compared with placebo. Data on SBP and DBP were reported by 12 randomized controlled trials, with a total of 415 participants allocated to the hibiscus group and 404 to the control group.
Two studies compared Hibiscus sabdariffa to black tea; one study compared it to captopril and one to lisinopril. The studies found that hibiscus had greater blood pressure reduction than tea but less than the ACE inhibitors.
One clinical trial revealed that sour tea can be an effective medication for lowering blood pressure in individuals with stage 1 hypertension.
Limitations: A well-conducted systematic review concluded that there was no reliable evidence to recommend Hibiscus sabdariffa as a treatment for primary hypertension in adults, and this conclusion was considered likely to be reliable. None of the trials in that early review provided data on adverse events. The high heterogeneity (I² = 95%) in more recent meta-analyses also limits certainty. Evidence to date supports a modest antihypertensive effect, particularly in individuals with elevated baseline blood pressure, but the clinical significance and long-term effects remain unclear.
4.2 Blood Lipids
Use of H. sabdariffa has been found in some studies to improve lipid profile, reducing serum levels of total cholesterol, LDL, and total triglycerides.
One randomized controlled clinical trial investigated the hypolipidemic effects of sour tea in patients with diabetes and compared them with those of black tea. In this sequential randomized controlled clinical trial, 60 patients with diabetes were recruited and randomly assigned into two groups: sour tea (ST) and black tea (BT), instructed to consume the tea two times a day for 1 month. A significant decrease in the mean of total cholesterol, LDL-cholesterol, triglycerides, and Apo-B100 was seen in the sour tea group. In the black tea group, only HDL-C showed significant change. The results showed that sour tea has a significant effect on blood lipid profile in patients with diabetes.
Evidence from chronic studies suggests that high doses (>1 g/day) affect blood pressure, and doses between 500 and 1000 mg/day affect lipids.
Limitations: A systematic review and meta-analysis found that the available evidence from RCTs does not support the efficacy of Hibiscus sabdariffa in lowering serum lipids, and that further rigorously designed trials with larger sample sizes are warranted to confirm the effects on serum lipids. One individual RCT in hypertensive patients comparing hibiscus to black tea over 30 days found no significant differences in lipid outcomes between the two groups. There was no significant difference between pre- and post-experiment values within the two groups, and an upward trend in total cholesterol, HDL, and LDL cholesterol was evident in both groups. Overall, the evidence for lipid lowering is mixed and insufficient to draw definitive conclusions.
4.3 Blood Glucose and Diabetes
Thanks to numerous active compounds, including polyphenols, polysaccharides, organic acids, and pectins, hibiscus is reported to exhibit hypoglycemic, antioxidant, hypotensive, and anti-lipidemic activities.
Daily consumption of H. sabdariffa extract appears to significantly improve blood pressure in prehypertensive and mildly hypertensive patients and patients with type 2 diabetes. Intake of hibiscus can also facilitate a better postprandial glucose response.
Inhibition of pancreatic α-amylase and intestinal α-glucosidase enzymes by organic acids in hibiscus is one proposed mechanism for its hypoglycemic effects.
Limitations: The majority of evidence for hypoglycemic effects comes from animal models. Human clinical trial data are limited, and most reviews note that further well-designed trials are needed to confirm antidiabetic effects.
4.4 Antioxidant and Anti-inflammatory Effects
Results from reviews suggest that H. sabdariffa is able to take up free radicals, inhibiting, for example, LDL oxidation. Anthocyanins in H. sabdariffa have been shown to be able to inhibit LDL oxidation and possibly to decrease the risk of atherosclerosis.
Roselle exhibits anti-inflammatory properties, as evidenced by its impact on inflammatory markers such as MCP-1 and TNF-α. Additionally, HS extracts have shown notable antibacterial efficacy against various strains, with a potential role in urinary tract infection management.
In one clinical study, a statistically significant reduction in TNF-α was found at baseline, four weeks, and eight weeks between treatment groups (P = 0.026), though no significant difference was observed among other inflammatory markers. In an investigation by Joven et al., individuals with metabolic syndrome who received polyphenols derived from the HS calyx for four weeks showed notable anti-inflammatory effects including a reduction in interleukin IL-6, IL-1β, and IL-8, and demonstrated potent antioxidant properties manifested through a decrease in 8-isoprostane-F2α levels and an elevation in serum paraoxonase activity.
It is notable that MCP-1 was present in healthy subjects and was significantly lowered after hibiscus treatment.
4.5 Diuretic Activity
The diuretic and natriuretic effect of Hibiscus sabdariffa aqueous extract showed a dose-dependent behavior in animal studies. The pharmacological constants of natriuretic effect were ED50 = 86 mg/kg and Emax = 0.9 mEq/100 g/5 h; and in a kidney in situ model, renal filtration increased 48% with the aqueous extract, with an additive effect when perfused with furosemide.
In an animal study, the Hibiscus sabdariffa aqueous extract at all doses showed remarkable diuretic activity during an 18-hour period, comparable to hydrochlorothiazide.
Limitations: Diuretic data in humans is sparse. The evidence for human diuretic effects remains largely preclinical (animal-based).
4.6 Uric Acid and Renal Stone Effects
One study evaluated the uricosuric clinical effects of HS tea (1.5 g of HS powder in 150 mL of boiling water twice a day for 15 days) in healthy and former renal stone subjects (aged 36 to 65 years). After taking the HS tea, increases in oxalate, citrate, and uric acid excretion levels were observed in both groups; in the renal stone subjects, the effect was significantly increased, which could provide long-term effect benefits for hyperuricemia in gout disease.
Daily consumption of 15 g of HS orally as an infusion before breakfast for 28 days slightly decreased creatinine and uric acid levels in essential hypertensive patients.
4.7 Antimicrobial Activity
Studies conducted in vitro and on animal models have confirmed the antimicrobial properties of HS. Aqueous extract of Hibiscus sabdariffa and its bioactive constituent protocatechuic acid (PCA) have been evaluated in vitro for antiviral activity against HSV-2 clinical isolates. PCA showed potent anti-HSV-2 activity compared with that of acyclovir, with EC₅₀ values of 0.92 and 1.43 µg·mL⁻¹, respectively.
In one clinical trial, oral supplementation with tablets composed of Hibiscus sabdariffa and Boswellia serrata extracts twice a day for seven days reduced symptoms related to urinary tract infections and their recurrence, similar to what was observed with antibiotics. These effects were attributed to the sambubiosides and their anti-inflammatory and antimicrobial properties.
Limitations: Most antimicrobial evidence for hibiscus is in vitro or animal-based. Human clinical data is very limited, and the UTI study cited used a combination product.
4.8 Body Weight and Metabolic Syndrome
Promising results have been detected in human clinical trials where consumption of H. sabdariffa extract for 12 weeks resulted in body weight loss, reduced BMI, reduced body fat, reduced waist-to-hip ratio, and reduced liver steatosis in subjects with a BMI ≥ 27 and between the ages of 16 and 65 years.
Multiple putative modes of action relating to the plant's antiobesity, antimetabolic disorder, and hepatoprotective effects have been proposed, including downregulation of relevant genes.
Limitations: Evidence for weight-loss effects is preliminary. Larger, well-controlled trials are required before firm conclusions can be drawn.
4.9 Cognitive Function
There are no human studies assessing the effects of hibiscus on cognition prior to 2025. The results of a first trial of hibiscus on cognitive performance in humans demonstrate modest beneficial effects on verbal memory, executive function, and pattern separation after acute consumption of hibiscus. Hibiscus intake also facilitated a better postprandial glucose response. However, effects on blood pressure in acute settings were not detectable. Further large-scale studies are required to validate the clinical efficacy of hibiscus on cognitive performance in humans.
Limitations: Cognitive effects are based on a single initial study; evidence is very preliminary.
5. Body Systems and Health Areas
- Cardiovascular system: Blood pressure modulation, LDL oxidation inhibition, potential lipid-lowering effects.
- Metabolic/Endocrine system: Blood glucose regulation, insulin sensitivity, body weight and adiposity.
- Renal/Urinary system: Diuretic and natriuretic activity, uric acid excretion, potential role in urinary tract infection management.
- Immune/Inflammatory system: Reduction of pro-inflammatory cytokines (TNF-α, IL-6, IL-1β, IL-8, MCP-1), COX-1/COX-2 inhibition.
- Hepatic system: Hepatoprotective effects reported in animal models and preliminary human data.
- Antimicrobial: In vitro and animal evidence against bacterial and viral pathogens; limited human data.
- Cognitive: Very preliminary evidence for effects on verbal memory and executive function.
The most-reported HS health benefits are its antihypertensive, antidyslipidemic, hypoglycemic, body fat mass reduction, nephroprotective, antianemic, antioxidant, anti-inflammatory, and anti-xerostomic activities; these effects are associated with the phytochemicals found in HS.
6. Dosage Forms and Reported Dosages
Dosages used in clinical studies vary considerably depending on the preparation, indication, and study design. The following are dosages reported in the research literature:
- Trials investigating the hypotensive effect of hibiscus have evaluated oral daily dosages of an infusion prepared with 10 g of dry H. sabdariffa calyx in water (standardized to 9.6 mg of anthocyanin content per dose), or an herbal medicinal product prepared from H. sabdariffa dried calyx extract (standardized to 250 mg of total anthocyanins per dose); treatment duration in these studies was 4 weeks.
- In a 2014 systematic review and meta-analysis investigating blood pressure effects, H. sabdariffa aqueous extract dosages used included 2 "spoonfuls" daily, 100 mg daily, and 3.75 g daily for a duration of 15 days to 6 weeks.
- One clinical study of urinary/creatinine effects used 15 g of HS orally as an infusion before breakfast for 28 days.
- A uricosuric study used 1.5 g of HS powder in 150 mL of boiling water, administered twice a day for 15 days.
- In a study of lipid effects in diabetic patients, 60 patients consumed sour tea twice daily for 1 month.
- In the studies included in one meta-analysis, mild gastrointestinal symptoms were reported using 1 g of hibiscus extract after the first week of supplementation, and no other adverse effects were reported up to doses of 10 g/day.
Evidence from chronic studies suggests that high doses (>1 g/day) appear to affect blood pressure, and doses between 500 and 1000 mg/day appear to affect lipids.
7. Safety Considerations and Drug Interactions
General Safety Profile
Available evidence suggests that Hibiscus sabdariffa extracts have a favourable safety profile in humans at doses below 32.3 mg/kg body weight/day and at 500 mL/day of tea with concentrations below 30 g/L for up to 6 months.
Hibiscus is considered safe for consumption, with no evidence of toxicity in rodent studies up to 5000 mg/kg in an acute dose or chronic feeding up to 200 mg/kg over 3 months. In one meta-analysis, authors of one study reported mild gastrointestinal symptoms using 1 g of hibiscus extract after the first week of supplementation; however, these symptoms subsided within 1 week. No other adverse effects were reported across the included studies in this analysis at doses up to 10 g/day.
Insufficient evidence on longer duration of consumption still raises concern, as indicated by preclinical toxicity studies assessing the liver, kidneys, and male reproductive organs.
Studies carried out in animals and humans have primarily demonstrated either no change or decreases in measures related to liver (AST and ALT liver enzymes) and kidney (creatinine, blood urea nitrogen, and urea) function. However, at doses of 300 mg/kg/day of H. sabdariffa over a 3-month period, an adverse effect on liver enzymes was observed, suggesting that at very high doses the extract could be hepatotoxic.
Several studies have indicated that high doses of hibiscus tea for relatively long periods might have diverse influences on reproductive systems, kidney, and liver functions.
Reproductive Considerations
A rat experiment using H. sabdariffa calyx extract dosages of up to 4.6 g/kg daily over 12 weeks found a reduction in epididymal sperm count, evidence of histological damage, and disintegration of sperm cells. Conversely, a study evaluating the effects of hibiscus 1 g/kg/day on cisplatin-induced reproductive toxicity found a protective effect as measured by sperm motility, attributed to antioxidant activity. Information regarding safety and efficacy in pregnancy and lactation is lacking.
Drug Interactions
Previous preclinical and clinical studies showed that ingestion of H. sabdariffa extract with conventional pharmaceuticals such as acetaminophen, chloroquine, hydrochlorothiazide, and simvastatin can change the pharmacokinetics profile of the primary drug, potentially affecting treatment efficacy.
One study noted that the combined intake of low-dose aqueous hibiscus extract and low-dose simvastatin resulted in better reduction of total cholesterol (38.3%) and triglycerides (57.4%) compared to low-dose simvastatin alone. However, there was a significant herb-drug interaction, with the hibiscus extract reducing the peak concentration of simvastatin by 18.0% and increasing its clearance by 44.6% (P < 0.05). The study concluded that the combined administration of simvastatin and hibiscus should not be encouraged until more clinical studies are done.
Concomitant intake of hibiscus (20–40 mg/kg body weight) with the diuretic drug hydrochlorothiazide (10 mg/kg) significantly increased urine volume in experimental rats over a 24-hour sampling period, which increases the risk of dehydration. However, the dose of the drug used in that study does not translate to a physiological dose for human consumption.
A study investigating the effects of co-administration of Hibiscus sabdariffa aqueous extract and captopril (an ACE inhibitor) in rats found that the hibiscus extract did not enhance the blood pressure-lowering effects of captopril. However, more studies, especially in humans, need to be done on the potential interaction of hibiscus with ACE inhibitors and other antihypertensive medications.
Studies in healthy volunteers have shown altered chloroquine, acetaminophen, and diclofenac pharmacokinetics. The clinical effects of these interactions have not been fully evaluated.
Research Gaps
There is a recognized need for more well-designed controlled clinical studies in humans on the kinetics of hibiscus extracts, their ingredients, and the related effects of their long-term consumption. Clinical studies to date have exhibited some limitations; thus, further studies are required to validate the clinical efficacy of HS in large-scale studies with higher doses and a good experimental design.
References
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