ASK DIS: Herbal Interactions: Rooibos

Also known as red bush tea, is native to South Africa.
It has gained much attention for clinical purposes in the case of nervous tension, allergies (dermatitis), and various indigestive problems.
Rooibos tea contains a large amount of flavonoids and acts as a potent antioxidant.
In Africa, it has been used to treat malignancies and inflammatory disorders.
Although no significantly active compounds exist in the leaves, red bush tea has a high vitamin C content. It is being investigated as an anti-cancer drug and as a prevention for brain damage caused by aging

There is no proven safe or effective dose of rooibos. Traditionally, 1 teabag or teaspoon to 8 ounces of hot water has been used

Avoid in individuals with a known allergy or hypersensitivity to Aspalathus linearis, its constituents or related members of the Fabaceae/Leguminosae family.
Other members of this family include peas, soybeans, clover, and peanuts.

Little evidence is available to describe the adverse effects of rooibos. Rooibos is likely safe when ingested as a tisane (herbal infusion) in food amounts. However, use cautiously in patients taking drugs or herbs metabolized by cytochrome P450 enzymes, as there is unclear evidence whether or not rooibos affects these enzymes
The Memorial Sloan Kettering Cancer Center reports rooibos demonstrates estrogenic activity
Sloan Kettering notes a case report of liver damaging after consuming rooibos
notes a lack of reports suggesting rooibos carries any risk of toxicity

Rooibos is not recommended in pregnant or breastfeeding women due to a lack of available scientific evidence.

There is mixed evidence on whether or not rooibos affects P450 metabolism. In theory, rooibos may interfere with the way the body processes certain drugs using the liver's "cytochrome P450" enzyme system. As a result, the levels of these drugs may be increased in the blood, and may cause increased effects or potentially serious adverse reactions.
contains a number of antioxidants. While usually associated with positive actions, some concern exists over whether or not antioxidant-rich supplements interfere with the actions of chemotherapy drugs

Evidences of use:

When looking at the main claim, the bioactives in Rooibos appear to be relatively potent antioxidant but even when tested in vitro (outside of a living body) they are not as potent as the Green Tea Catechins; the main bioactive, aspalanthin, also has a pretty poor absorption in living models
It is said that the tea can alleviate intestinal distress and it does appear to have some relaxing effects in the intestines, but there is no evidence in humans at this point in time (and for that claim, Peppermint would be a more prudent option)

References:

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