- Green tea is rich in beneficial plant compounds but sipping on the tea isn’t completely risk-free.
- Many of the active compounds in green tea interfere with some medications, like blood thinners and stimulants.
- You may want to limit or avoid green tea if you’re pregnant, caffeine sensitive or have anemia.
Since around 3000 BC, people have enjoyed green tea for its many health benefits and its distinctive flavor. In recent years, research has uncovered its supportive connections to weight loss, improved focus, anti-aging effects and cancer prevention. “Green tea is rich in antioxidants and loaded with polyphenols, especially catechins (like EGCG), which can help fight inflammation and reduce oxidative stress,” says Sheeri Jonnala, M.S., RD. But it’s these same bioactive substances in green tea that may cause dangerous interactions with several medications.
“While green tea is widely considered a healthful beverage, there are certain circumstances where its use may not be appropriate or should be approached with caution,” says Jessica Beal, Pharm.D. Here are five medications that may interact with green tea.
1. Blood Thinners
Anticoagulant medications that thin the blood by reducing the clotting action of vitamin K, like warfarin (also known as Coumadin or Jantoven), may be less effective when taken with large amounts of green tea. One of the most important variables to consider when taking warfarin is the amount of vitamin K you’re consuming through food or supplements, and maintaining a consistent intake. “While the vitamin K content of green tea is much lower than that of leafy greens, large or sudden increases in green tea intake could reduce warfarin’s effectiveness, leading to a risk of clotting,” says Beal.
While a cup or two of green tea is unlikely to affect your INR levels (the measure of how long it takes your blood to clot), cases of reduced warfarin effectiveness have been reported with the intake of one gallon of green tea or more per day.
2. Stimulants
A cup of regular green tea contains about 30 milligrams of caffeine, a nervous system stimulant. While it has less caffeine than what you’ll find in a cup of coffee, it can still add up and interact with other medications that have stimulating effects on the body, such as those used to treat attention-deficit hyperactivity disorder (ADHD).
“When combined with stimulant medications, there can be an additive effect, leading to elevated heart rate, increased blood pressure, anxiety or insomnia,” explains Beal. If you take a stimulant medication, choosing decaffeinated green tea may be the best option.
3. Iron Supplements
Iron deficiency anemia is a major public health concern, affecting up to 18% of women and a smaller percentage of men around the world. Anemia can lead to extreme fatigue, brittle nails, restless legs and mood disorders, and is often treated with iron supplements to quickly and effectively increase levels.
Unfortunately, drinking green tea may not only interfere with the absorption of iron supplements but may also increase the risk of developing iron deficiency anemia in the first place. While the research is limited and somewhat contradictory, a few studies have found that compounds, including phytates, calcium, tannins, and specific polyphenols in green tea, may limit the absorption of non-heme iron, which is already poorly absorbed by the body., If iron deficiency is a concern, separating green tea from your iron supplements by an hour or two may help eliminate any absorption issues, Beal recommends.
4. Certain Mental Health Medications
Green tea may increase drug levels of antipsychotic medications such as Clozapine (Clozaril) or Olanzapine (Zyprexa) and the antidepressant Amitriptyline (Elavil), explains Beal.,,“Caffeine in green tea is metabolized by the liver enzyme CYP1A2, the same pathway used by these medications,” adds Beal, explaining that the caffeine competes for metabolism, increasing the drug levels and the risk of adverse effects like sedation, significant blood pressure changes or seizures.
Who Should Avoid Green Tea?
Aside from medications, here are some instances where you may want to avoid or limit the amount of green tea you drink:
- You’re pregnant or breastfeeding: While limiting caffeine to less than 200 to 300 milligrams per day during pregnancy and breastfeeding is recommended, green tea may also affect nutrient availability to a growing fetus. “Green tea can reduce folate absorption, a nutrient crucial for avoiding neural tube defects,” says Jonnala.
- You have anemia: “Green tea contains tannins and catechins that can bind non-heme iron and reduce absorption, making it harder to correct low iron levels,” says Beal.,
- You’re sensitive to caffeine: While green tea has much less caffeine than coffee or energy drinks, it may still impact your sleep, heart rate, anxiety levels or cause migraines if you’re sensitive to its effects.
- You have hypotension: Green tea catechins have several activities that may reduce blood pressure, with a large review of randomized controlled trials finding that green tea may play a role in lowering both systolic and diastolic blood pressure in people with or without hypertension.
Our Expert Take
Green tea is rich in antioxidants and powerful plant compounds that offer plenty of health perks, but it isn’t completely risk-free. Many of the active compounds in green tea that provide benefits can interfere with certain medications, including blood thinners, stimulants, iron supplements, blood pressure medications, and some mental health drugs.
Drinking green tea could also do more harm than good if you’re pregnant, caffeine sensitive, have anemia, or struggle with low blood pressure. If you love green tea but take a medication or have a health condition, it’s best to check with your doctor and pharmacist to make sure it’s a safe option.