There are a few kinds of medication that can negatively interact with the polyphenols and caffeine in green tea. While some only cause a mild interaction, others may potentially cause serious health complications, so talk to your doctor before drinking green tea with any new prescription or supplement.
Some medications that can interact with green tea include the following:
1. Blood Thinners
People who take anticoagulant medications (blood thinners) like warfarin should review their green tea intake with their doctor.
Green tea contains vitamin K, which can make the medication less effective. Green tea also has other compounds that might increase the blood-thinning effect of these meds, which can be dangerous.
You may be able to drink some green tea while taking blood thinners, but the key is to have a consistent intake of vitamin K in your diet. Inconsistency causes shifts in the degree of anticoagulation, potentially lowering the drug’s effectiveness.
2. Statins
Drinking green tea may possibly reduce the absorption of some statins, like atorvastatin (Lipitor), according to a small study with 12 participants.
Green tea can affect other cardiovascular drugs, too. Polyphenols in green tea have been found to decrease the body’s distribution and absorption of rosuvastatin, a drug used for heart disease as well as for managing cholesterol.
That said, more studies surrounding green tea’s effect on statins are needed to further confirm these findings and to give more accurate guidance for green tea consumption.
3. Aspirin
Both aspirin and certain compounds in green tea can prevent your blood from clotting, and together they may increase your risk of bleeding. This hasn’t been thoroughly researched and applies more if you’re consuming higher doses of green tea or epigallocatechin gallate as a supplement.
Discuss with your doctor if you are on aspirin or have cardiovascular or clotting issues and are taking or plan to increase your green tea intake.
4. Certain Mental Health Medications
Green tea can reduce the blood levels of lithium in those who take the medication for mania or bipolar disorder. And if you stop drinking green tea abruptly while on lithium, it can cause your lithium levels to spike.
The caffeine in green tea can also reduce the sedative effects of certain benzodiazepines to treat anxiety, such as alprazolam (Xanax).
When taken with green tea, MAOIs (monoamine oxidase inhibitors) for depression can cause an abnormal spike in blood pressure, leading to a hypertensive crisis. Some of these medications include selegiline (Zelapar) and phenelzine (Nardil).
And because green tea acts as a mild stimulant, you shouldn’t drink it alongside other stimulants — like amphetamines (Adderall) for ADHD, for example.
5. Weight Loss Drugs
Ephedrine (Ephedra) is an ingredient that was once often found in weight loss supplements. However, the U.S. Food and Drug Administration (FDA) prohibited the sale of dietary supplements that have ephedra in 2004 because it presents an unreasonable risk of illness. There are still forms of it sold outside the United States.
6. Certain Antibiotics
Green tea, specifically the caffeine content, may make a certain class of antibiotics called quinolone antibiotics (which treat a variety of bacterial infections) more effective and increase the risk of side effects while taking them. Always talk to your doctor before taking antibiotics with caffeine to make sure there are no interactions.
Some examples of these types of antibiotics include the following:
ciprofloxacin (Cipro)
enoxacin (Penetrex)
grepafloxacin (Raxar)
norfloxacin (Chibroxin, Noroxin)
sparfloxacin (Zagam)
trovafloxacin (Trovan)
7. Beta-Blockers and ACE Inhibitors
The caffeine in green tea may increase blood pressure in people who take beta-blockers for high blood pressure or heart disease. Some of these medications include nadolol, atenolol, and bisoprolol.
A small study also found that taking green tea extract could reduce the absorption and effectiveness of the ACE inhibitor lisinopril (which is prescribed to reduce blood pressure).
8. Iron and Folic Acid
Talk to your doctor if you take iron supplements and want to drink green tea. Green tea can affect the way iron is absorbed in your body. The flavonoids in tea can bind to nonheme iron, keeping it from absorbing in your intestines.
Likewise, caffeine can also reduce the absorption of folic acid and may reduce your folic acid levels, especially in people who are pregnant.
9. Certain Herbs
There is some evidence to suggest that drinking caffeine while taking bitter orange extract can increase blood pressure and heart rate.
Talk to your doctor about any herbs or natural supplements you are taking. They can let you know whether you can drink green tea or take green tea extracts while using these substances. Note that supplements are not regulated by the FDA, so just like with green tea, it’s important to make sure they don’t interact with any of your other medications as well.