Green tea catechins and how they change drug levels in people
What it found
In clinical studies, green tea lowered the amount of most tested drugs reaching the bloodstream by 18 to 99 percent.
One drug level rose by 50 percent, while four others were not affected.
What they found
Studies in people
Lower drug levels
Most analyses, about 72 percent, found that drinking green tea lowered the amount of drug reaching the bloodstream by 18 to 99 percent. This happened with ten different medicines, including some for cholesterol, blood pressure, and allergies.
Higher drug levels
One analysis, about 6 percent, found a 50 percent rise in the amount of sildenafil reaching the bloodstream when taken with green tea.
No change in levels
For 22 percent of the analyses, green tea did not change drug levels. The unaffected medicines included fluvastatin, pseudoephedrine, simvastatin, and tamoxifen.
Real patient reports
Case reports linked changes in drug levels from green tea to changes in how well medicines worked or their side effects. Examples involved the drugs nadolol and erlotinib.
Other findings
How interactions happen
Green tea catechins are thought to block proteins that help pull drugs through the gut wall. They may also push drugs back into the gut or make them harder to dissolve.
What the authors conclude
- They say more research is needed to use existing evidence to predict other important interactions between green tea and medicines.
- The authors advise developing clear guidance for patients and doctors about drinking green tea while on medication.
How it was done
People often drink green tea or take it as a supplement while also using prescription medicines. They may not know that compounds in green tea can change how well those medicines work.
The authors gathered results from clinical studies looking at how green tea catechins changed drug levels in people taking real medications. They examined data for multiple drugs to see if green tea raised or lowered the amounts reaching the bloodstream.
What it can’t tell you
- We summarised it from the abstract only.
- This work gathers past studies rather than testing new treatments, so it cannot prove green tea directly caused every change seen.
- Not all medicines have been studied with green tea, so scientists do not yet know which other drugs might be affected.
Who paid
- Authors work at
- University of Sydney, Australia
The paper
- Title
- Green Tea Catechins as Perpetrators of Drug Pharmacokinetic Interactions
- Type
- ReviewThe authors read earlier studies and describe what they found. It isn’t a new study.
- Evidence
- Studies in people
- Summarised from
- Abstract only
- Cite
- Kyriacou NM, Gross AS, McLachlan AJ (2025). Green Tea Catechins as Perpetrators of Drug Pharmacokinetic Interactions. Clinical pharmacology and therapeutics. doi:10.1002/cpt.3547PubMed 39748104DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error