In short trials, hibiscus tea has few reported side effects; a 2015 trial of 80 people reported none over 4 weeks. Its real risks come from lowering blood pressure and from how it alters some medicines.
Every interaction below names the study, the species and the size of the effect, because most of them rest on a few volunteers or a few rats.
Quick Answer: What Are the Side Effects of Hibiscus Tea?
Short trials report few side effects, mainly more urination and, in sensitive people, nausea or dizziness. The bigger risks are interactions: it can add to blood pressure drugs, cut chloroquine levels about 71% in healthy men and lower simvastatin exposure to 0.646 of normal. Avoid it in pregnancy and with low blood pressure.
Key Takeaways
- Short trials report few side effects; 1 trial of 80 reported none.
- Hibiscus cut chloroquine blood levels by about 71% in healthy men.
- In 6 volunteers, simvastatin exposure fell to 0.646 of its usual level.
- Rats showed higher hydrochlorothiazide levels, and captopril levels fell over 80%.
- We found only 2 trials adding hibiscus to a blood pressure drug.
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Side Effects People Actually Report
Most hibiscus trials lasted 2 to 12 weeks and reported few problems. The effects people notice follow from how it works: more urine, and in some people a light-headed or queasy feeling, especially on an empty stomach.
- More urination: hibiscus acts as a mild diuretic.
- Nausea or dizziness: reported by sensitive volunteers in a 16-day study.
- Light-headedness: possible if your readings were already low.
- Stomach upset: listed on our product page; the tea is tart and acidic.
The 16-day study was looking at aluminium in the tea, and noted the complaints in passing.[1]In Vitro Digestibility of Aluminum from Hibiscus sabdariffa Hot Watery Infusion and Its Concentration in Urine — Biological Trace Element Research (2016) View source The wider picture is in our overview of hibiscus tea.
Low Blood Pressure and Dizziness
Hibiscus lowers pressure more in people who start high. Nobody has tested it in people with low blood pressure, so the safest reading of the evidence is to skip it if your readings already run low or you faint easily.
- Starting high: the higher-pressure half of the 2010 trial fell 13.2 mmHg.
- Starting normal: a smaller effect is likely, not zero.
- Starting low: 0 trials, so avoid it.
- On medication: the effects could add up.
Pooled trials report systolic falls of about 4.7 mmHg or more.[2]The efficacy of sour tea (Hibiscus sabdariffa L.) on selected cardiovascular disease risk factors: A systematic review and meta-analysis — Phytotherapy Research (2020) View source
Blends That Already Contain Hibiscus
The easiest way to take too much hibiscus is to take it twice without noticing. Several of our own products list hibiscus as an ingredient, so count each one as a source before adding another.
- Pressure Balance: lists hibiscus among 12 herbs, licorice included.
- Vitamin C with Hibiscus: 1,000 mg of vitamin C plus hibiscus.
- Anti-Oxidant Tea: green tea, hibiscus and other botanicals.
- Hibiscus Citrus Tea: 20 bags of hibiscus tea.
If you want 1 source you can count, choose a single-ingredient hibiscus capsule or 1 tea, not both.
Blood Pressure Medicine and Diuretics
This is the interaction that matters most, and it is the least studied in people. The trials that report it enrolled people not taking blood pressure drugs, so the combination rests on animals and 2 small supervised trials.
| Drug | Who was studied | What hibiscus changed |
|---|---|---|
| Hydrochlorothiazide | Rats and rabbits | Higher, longer drug levels and more urine |
| Captopril | Rats | Drug exposure fell to about 17% |
| Losartan | Rats with high blood pressure | Drug exposure roughly doubled |
| Valsartan | 72 people with mild kidney disease | Pressure fell in both groups over 90 days |
In rats and rabbits, hibiscus raised and prolonged hydrochlorothiazide levels and increased urine output.[3]Herb-drug interaction between the extract of Hibiscus sabdariffa L. and hydrochlorothiazide in experimental animals — Journal of Medicinal Food (2011) View source In rats it cut captopril exposure to about 17% of normal.[4]Pharmacokinetic Herb-Drug Interaction between Hibiscus sabdariffa Calyces Aqueous Extract and Captopril in Rats — Evidence-Based Complementary and Alternative Medicine (2020) View source
Effects that run in opposite directions in different animals are why nobody can predict the combination for you. Your prescriber and your home readings can.
Other Medicines With Human Data
A handful of tiny human studies have tested hibiscus alongside a single dose of a drug. Each one is small, and each one changed something, which is why we list them with their numbers rather than as a vague warning.
| Medicine | Who was studied | What hibiscus changed |
|---|---|---|
| Chloroquine | Healthy men | Drug exposure fell from 7.52 to 2.16 mg.h/L |
| Simvastatin | 6 volunteers | Exposure ratio 0.646; clearance up 44.6% |
| Acetaminophen | 6 men | Absorption unchanged; clearance up 11.69% |
| Diclofenac | Healthy volunteers | Less drug excreted in urine |
| Warfarin | 1 case report | INR rose sharply; settled after stopping |
The chloroquine study gave the drug with karkade on an empty stomach and found about 71% less in the blood.[5]Significant reduction in chloroquine bioavailability following coadministration with the Sudanese beverages Aradaib, Karkadi and Lemon — Journal of Antimicrobial Chemotherapy (1994) View source Simvastatin exposure fell outside the bioequivalence range.[6]In vivo pharmacodynamic and pharmacokinetic interactions of Hibiscus sabdariffa calyces extracts with simvastatin — Journal of Clinical Pharmacy and Therapeutics (2017) View source
The acetaminophen change was modest.[7]Effect of zobo drink (Hibiscus sabdariffa water extract) on the pharmacokinetics of acetaminophen in human volunteers — European Journal of Drug Metabolism and Pharmacokinetics (2004) View source The warfarin report is 1 case, not proof.[8]Possible Interaction Between Hibiscus and Warfarin Resulting in Severe International Normalized Ratio Elevation: A Case Report — Cureus (2026) View source
Diabetes Medicines
Pooled trials found hibiscus lowers fasting glucose only slightly, by about 3.7 mg/dL. That is small, but in rats it added to glibenclamide, so anyone on insulin or a sulfonylurea should mention it to the prescriber.
- Human effect: fasting glucose about 3.7 mg/dL lower in pooled trials.
- Rats: extract plus glibenclamide lowered glucose together.
- Practical step: check readings more often for the first 2 weeks.
- Who to tell: your prescriber or diabetes nurse.
The rat study ran for 28 days.[9]Effect of Co-administration of Glibenclamide and Aqueous Calyx Extract of Hibiscus Sabdariffa in Streptozotocin-Induced Diabetic Rats — Nigerian Journal of Physiological Sciences (2021) View source
Pregnancy and Breastfeeding
There are 0 human trials of hibiscus in pregnancy. The cautions come from rat studies of offspring and from aluminium in the infusion, and together they are enough to say: avoid it while pregnant or breastfeeding.
- Human trials: 0.
- Rats: delayed puberty in offspring of mothers given hibiscus.
- Aluminium: up to 1.2 mg per litre in hibiscus infusions.
- Breastfeeding: no human data.
We answer the pregnancy question in full, including what to do if you already drank some.
Kidneys and the Liver
Hibiscus increases urine flow, and people with kidney disease often ask whether that is a problem. In a 4-week trial in untreated hypertension it raised creatinine clearance, and it raised urine volume more than lisinopril did.
- Kidney function: creatinine clearance up over 4 weeks.
- Stones: 2 small human urine studies, with mixed signals.
- Liver, rats: no chronic toxicity at 200 mg/kg for 270 days.
- Liver, people: a 2025 review found a minor, clinically insignificant enzyme rise.
The clearance finding comes from 78 newly diagnosed patients.[10]Does consumption of an aqueous extract of Hibiscus sabdariffa affect renal function in subjects with mild to moderate hypertension? — Journal of Physiological Sciences (2017) View source The 270-day rat study found no chronic toxicity.[11]Toxicity studies of the water extract from the calyces of Hibiscus sabdariffa L. in rats — African Journal of Traditional, Complementary and Alternative Medicines (2013) View source
Stones, oxalate and kidney disease are covered in the kidney and oxalate question.
How to Use It Safely
For a healthy adult who takes no regular medicine and is not pregnant, hibiscus has a reassuring short-term record. These habits cover most of the practical risk without making a simple drink complicated.
- One source: not a capsule plus a blend plus 3 cups.
- Tablets with water: especially chloroquine and statins.
- Tell your prescriber: about any daily hibiscus.
- Review: at 6 weeks, with your readings.
Stop and seek advice if you feel faint, notice a racing or very slow pulse, or bruise easily while taking warfarin.
Speak to a Clinician First If
- You take blood pressure medicine or a diuretic such as hydrochlorothiazide
- You take chloroquine, simvastatin, warfarin or another medicine with a narrow margin
- You take insulin or another glucose-lowering medicine
- You are pregnant, trying to conceive or breastfeeding
- You have kidney disease, kidney stones or blood pressure that already runs low
Frequently Asked Questions
Who should not drink hibiscus tea? +
People who are pregnant or breastfeeding, anyone with low blood pressure, and anyone on blood pressure drugs, diuretics, chloroquine, simvastatin or warfarin without agreement. Kidney disease is a 6th reason to ask first.
What not to mix with hibiscus tea? +
Chloroquine, simvastatin and acetaminophen all showed changed levels in small human studies, and hydrochlorothiazide did in rats. Also avoid stacking 2 hibiscus products.
Can I drink hibiscus tea if I take high blood pressure medicine? +
Only with your prescriber's agreement. We found only 2 trials adding hibiscus to a blood pressure drug, both supervised, and the animal studies show unpredictable effects.
How does hibiscus tea interfere with blood pressure medicine? +
In 2 ways. Its own effect can add to the drug's, and it can change drug levels: in rats it cut captopril exposure by over 80% but roughly doubled losartan's.
Why do I feel weird after drinking hibiscus tea? +
Possibly a fall in blood pressure, or its tartness on an empty stomach. In a 16-day study, a few sensitive volunteers reported nausea and dizziness.
Why do I pee so much after drinking hibiscus tea? +
Hibiscus acts as a mild diuretic. In a 4-week trial it increased urine volume more than lisinopril did.
Are there any dangers to drinking hibiscus tea? +
For most healthy adults, few in the short term. The dangers are interactions, pregnancy and low blood pressure; 1 case report from 2026 also linked it to a sharp INR rise on warfarin.
Can hibiscus tea make low blood pressure worse? +
It may. 0 trials included people with low blood pressure, and its effect is a fall in pressure, so skip it if your readings already run low.
Does hibiscus affect warfarin? +
Possibly. A 2026 case report described a 59-year-old woman whose INR rose sharply after drinking hibiscus tea and settled after she stopped. 1 case cannot prove cause.
Is hibiscus tea bad for the liver? +
Not at usual amounts in the studies we read. Rats given 200 mg/kg daily for 270 days showed no chronic toxicity, and a 2025 review found only a minor enzyme rise in people.
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