Rooibos tea is caffeine-free and generally well tolerated, but certain people should limit or avoid it. Those with existing liver conditions, people on specific medications, anyone undergoing cancer treatment, and individuals with hormone-sensitive conditions all have reasons to be cautious. Here’s a closer look at each group and why rooibos may pose a problem.
People With Liver Conditions
At least one documented case of acute liver injury has been linked to daily rooibos consumption. A 52-year-old man developed signs of acute hepatitis and liver failure after drinking rooibos and buchu tea daily for about a month. His liver enzymes spiked to extreme levels, and a biopsy confirmed toxin-mediated liver injury. He recovered fully after stopping the tea.
The case was published in the ACG Case Reports Journal, and the authors noted that a South African hepatologist was aware of additional anecdotal cases of liver injury tied to rooibos and buchu tea, though the exact mechanism remains unclear. Because the tea in that case also contained buchu (another South African herb), it’s difficult to pin the damage on rooibos alone. Still, if you already have liver disease, elevated liver enzymes, or are taking medications that stress the liver, this is a real reason for caution.
People Taking Blood Sugar or Cholesterol Medications
Rooibos can interfere with the same enzyme systems your body uses to break down certain drugs. Lab research published in the journal Molecules found that rooibos extracts inhibit three key liver enzymes involved in processing common diabetes and cholesterol medications. The affected drug classes include thiazolidinediones (a type of diabetes pill), sulfonylureas (another class of blood sugar medication), and statins like atorvastatin.
When these enzymes are slowed down, medication can build up to higher-than-intended levels in your bloodstream, increasing the risk of side effects. Both fermented (red) and unfermented (green) rooibos showed this inhibitory effect, and the inhibition grew stronger with higher doses and longer exposure. If you take any of these medications, drinking large amounts of rooibos tea could change how your body processes them.
People Undergoing Cancer Treatment
Memorial Sloan Kettering Cancer Center specifically flags rooibos tea as a potential concern during chemotherapy. The antioxidant compounds in rooibos may interfere with the action of certain chemotherapy drugs, which sometimes work by generating cell-damaging molecules to kill cancer cells. Flooding your system with antioxidants during treatment could theoretically blunt that effect.
There is also a striking case involving a 38-year-old woman with acute myeloid leukemia who had undergone a bone marrow transplant. She was drinking more than 2 liters of rooibos tea per day, and this reduced the concentration of tacrolimus, an anti-rejection drug critical to preventing graft-versus-host disease. The drug levels dropped enough that she developed the very complication the medication was supposed to prevent. This is a clear example of how heavy rooibos consumption can alter drug levels in a clinically dangerous way.
People With Hormone-Sensitive Conditions
Rooibos contains quercetin, a plant compound with phytoestrogenic activity, meaning it can interact with estrogen receptors in the body. Research published in Physiological Research found that both rooibos extract and quercetin alone were able to bind to and downregulate estrogen receptors in ovarian cells. They also altered hormone output, increasing testosterone release while decreasing estrogen production, and blocked the effects of follicle-stimulating hormone on cell growth.
For most people drinking a cup or two of rooibos, these effects are unlikely to be noticeable. But if you have a condition that’s sensitive to hormonal shifts, such as certain breast cancers, endometriosis, or uterine fibroids, even mild estrogenic activity from a daily herbal tea is worth knowing about. The same applies if you’re taking hormonal therapies where precise estrogen levels matter, like hormone replacement therapy or fertility medications.
People on Blood Pressure Medications
A study in healthy volunteers found that a single serving of rooibos tea significantly inhibited angiotensin-converting enzyme (ACE) activity within 30 minutes, with the effect still measurable at 60 minutes. ACE is the same enzyme targeted by a widely prescribed class of blood pressure drugs. If you’re already taking medication to lower your blood pressure, adding a natural ACE inhibitor on top could push your blood pressure lower than intended, potentially causing dizziness, lightheadedness, or fainting. The effect was especially notable in people with a specific genetic variant of ACE (the ACE II genotype).
This doesn’t mean rooibos is dangerous for everyone with high blood pressure. For some people, the mild blood pressure-lowering effect could even be welcome. But if your blood pressure is already well controlled with medication, or if you’re prone to low blood pressure episodes, it’s worth factoring in.
What About Iron Absorption?
One common concern with tea is that it blocks iron absorption, which matters for people with anemia. Rooibos actually performs well here. A study comparing rooibos tea, black tea, and plain water found that iron absorption averaged 7.25% with rooibos, compared to just 1.70% with black tea and 9.34% with water. The difference between rooibos and water was not statistically significant, meaning rooibos barely affects iron uptake at all. So if you’ve been avoiding tea because of iron concerns, rooibos is a much better option than black or green tea.
What About Kidney Stones?
Oxalates in food and drinks can contribute to calcium oxalate kidney stones, which is why people prone to stones often monitor their oxalate intake. Rooibos is low-risk here. Analysis of herbal teas found that a cup of herbal tea (including rooibos varieties) contains a maximum of about 6 mg of oxalate. For comparison, a cup of black tea can contain 50 to 100 mg or more. If kidney stones are a concern for you, rooibos is one of the safer hot beverages available.
How Much Is Too Much
No official upper limit has been set for daily rooibos consumption. Most of the concerning cases involve either very high intake (over 2 liters per day in the tacrolimus case) or combination with other herbs like buchu. A few cups a day appears safe for healthy adults without the risk factors described above. The problems tend to emerge at high volumes, with long daily use, or when rooibos is combined with medications or other herbal supplements that share similar metabolic pathways.
If you fall into any of the groups above, you don’t necessarily need to eliminate rooibos entirely. But drinking it in large quantities or using concentrated rooibos supplements carries more risk than an occasional cup. Letting your healthcare provider know you drink it regularly helps them account for potential interactions with any treatments you’re receiving.