As a nutrition support pharmacist, you must take into account some important points regarding the interaction between drugs and green tea (Camellia sinensis). Many patients don't realize green tea may interfere with some medications. People often drink green tea for its possible health benefits or take green tea supplements for weight loss or other reasons. But now there's evidence of possible drug interactions...
Catechins in green tea seem to inhibit an organic anion-transporting polypeptide (OATP) that aids GI absorption of certain drugs. This OATP transporter is also inhibited by orange, apple, and grapefruit juice. This interaction is different than the better known one between grapefruit and some 3A4 drugs like atrorvastatin (Lipitor), simvastatin (Zocor), erythromycin (Erythrocin), Brilique, etc.
In one study, drinking 12 ounces (350 mL or 1.5 cup) of green tea twice daily or 1 cup 3 times per day for 2 weeks DECREASES nadolol levels by 85% and reduces blood pressure (BP) lowering effects (NOTE; nadolol is not available in Egypt). But the amount of catechins in green tea varies between products. Until we know more, caution patients on nadolol to avoid green tea or monitor their BP to make sure the drug is working. ANOTHER EXAMPLE, In healthy humans, taking green tea extract 300 mg or 600 mg along with atorvastatin reduces plasma levels of atorvastatin by approximately 24%. Atorvastatin is a substrate of organic anion-transporting polypeptides (OATPs). Research shows that two of the major catechins found in green tea, epicatechin gallate (ECG) and epigallocatechin gallate (EGCG), inhibit OATPs. Some OATPs are expressed in the small intestine and are responsible for the uptake of drugs and other compounds, which may have resulted in reduced plasma levels of atorvastatin. Do not take this combination.
| Table (1). Dosage and Administration of Green Tea | |
|---|---|
| ADULT/CHILDREN | Dosing & Administration |
| Adult | Green tea has most often been used as a beverage, a powder, or an extract. Doses of green tea generally provide up to 2500 mg catechins or 700 mg of epigallocatechin-3-gallate (EGCG) daily. |
| Green tea extract and beverages are often standardized to total catechin or EGCG content. Green tea beverages are typically standardized to contain 178-823 mg of total catechins per cup. | |
| Consuming green tea may reduce the absorption of iron from plant foods. To prevent this interaction, separate intake of green tea from meals. | |
Additionally, certain foods may reduce the absorption of active green tea constituents.
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| Children | Research is limited; typical dosing is unavailable. |
Monitor patients if they use green tea with other drugs absorbed via OATP such as atenolol (Blokium), ciprofloxacin (Cibrobay), levofloxacin (Tavanic), or levothyroxine (Eltroxin). If problems occur, recommend avoiding green tea or switch to a drug that doesn't rely on OATP for GI absorption. Tell patients not to worry about black tea, it doesn't have a high concentration of catechins. Green tea contains caffeine. In excessive amounts, caffeine can reduce potassium levels due to stimulation of the sodium-potassium pump and diuretics can also cause lower potassium levels. ALSO, concomitant use of green tea may reduce activity and bioavailability of supplementary folic acid as it appears to inhibit the enzyme dihydrofolate reductase. This enzyme is responsible for converting folic acid to its active form. Remember, drinking green tea may worsen anemia in people with iron deficiency. Use with caution.
REFERENCES
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Misaka S, Yatabe J, Müller F, Takano K, Kawabe K, Glaeser H, Yatabe MS, Onoue S, Werba JP, Watanabe H, Yamada S, Fromm MF, Kimura J. Green tea ingestion greatly reduces plasma concentrations of nadolol in healthy subjects. Clin Pharmacol Ther. 2014 Apr;95(4):432-8. Available at: https://ascpt.onlinelibrary.wiley.com/doi/10.1038/clpt.2013.241
Shitara Y, Maeda K, Ikejiri K, Yoshida K, Horie T, Sugiyama Y. Clinical significance of organic anion transporting polypeptides (OATPs) in drug disposition: their roles in hepatic clearance and intestinal absorption. Biopharm Drug Dispos. 2013 Jan;34(1):45-78. Available at: https://onlinelibrary.wiley.com/doi/10.1002/bdd.1823
Abdelkawy KS, Abdelaziz RM, Abdelmageed AM, Donia AM, El-Khodary NM. Effects of Green Tea Extract on Atorvastatin Pharmacokinetics in Healthy Volunteers. Eur J Drug Metab Pharmacokinet. 2020 Jun;45(3):351-360. Available at: https://pubmed.ncbi.nlm.nih.gov/31997084
Alemdaroglu NC, Dietz U, Wolffram S, Spahn-Langguth H, Langguth P. Influence of green and black tea on folic acid pharmacokinetics in healthy volunteers: potential risk of diminished folic acid bioavailability. Biopharm Drug Dispos. 2008 Sep;29(6):335-48. Available at: https://onlinelibrary.wiley.com/doi/10.1002/bdd.617
Norager CB, Jensen MB, Weimann A, Madsen MR. Metabolic effects of caffeine ingestion and physical work in 75-year old citizens. A randomized, double-blind, placebo-controlled, cross-over study. Clin Endocrinol (Oxf). 2006 Aug;65(2):223-8. Available at: https://pubmed.ncbi.nlm.nih.gov/16886964