Green Tea Side Effects: What You Need to Know Before You Drink

When you sip green tea, a widely consumed beverage made from the leaves of the Camellia sinensis plant, often praised for antioxidants and metabolic benefits. Also known as unoxidized tea, it’s not just a calming ritual—it’s a bioactive compound with real physiological effects. Most people think of it as harmless, even healthy. But drinking it daily, especially in large amounts or as concentrated extracts, can trigger side effects you didn’t see coming.

The biggest culprit behind green tea side effects is caffeine, a stimulant naturally present in green tea, with about 20–45 mg per cup, less than coffee but enough to affect sensitive individuals. If you’re prone to anxiety, insomnia, or rapid heartbeat, even two cups a day might be too much. Then there’s iron absorption, a process that green tea’s tannins can block, especially when drunk with meals—this matters if you’re anemic or rely on plant-based iron sources. People with low iron levels or those taking iron supplements often don’t realize their tea is reducing the supplement’s effectiveness.

Some of the most serious risks come from green tea supplements, high-dose capsules or extracts that concentrate catechins like EGCG, sometimes to 100 times the level found in brewed tea. There are documented cases of liver damage linked to these supplements—some leading to acute hepatitis or even liver failure. The FDA has issued warnings, and doctors now ask patients: "Are you taking green tea pills?" before diagnosing unexplained liver issues.

Green tea can also interfere with medications. It affects how your body processes blood thinners like warfarin, certain antidepressants, and beta-blockers. If you’re on any prescription, check with your pharmacist before adding green tea extract to your routine. Even regular brewed tea can cause problems if you’re drinking a lot—say, five or more cups daily.

It’s not all bad news. For most healthy adults, one to three cups of brewed green tea a day is safe and may even help with focus and heart health. But if you’re pregnant, have a liver condition, suffer from anemia, or take meds regularly, you’re not just a casual drinker—you’re a risk-taker without realizing it. The side effects aren’t theoretical. They’re in medical journals, ER reports, and patient stories.

Below, you’ll find real-world comparisons and case-based guides on how green tea interacts with medications, supplements, and health conditions. No fluff. Just what you need to know to drink it safely—or avoid it altogether.