Herbal Teas and Medications: Potential Interactions to Review

Many people reach for herbal teas thinking they’re harmless-just a warm, soothing drink. But if you’re taking prescription medications, that cup of chamomile, green tea, or hibiscus might be doing more than calming your nerves. It could be interfering with how your drugs work, sometimes in dangerous ways.

Why Herbal Teas Aren’t Just ‘Natural’

Herbal teas aren’t tea in the traditional sense. They don’t come from the Camellia sinensis plant. Instead, they’re made from roots, flowers, leaves, or seeds of other plants-chamomile, peppermint, ginger, hibiscus, St. John’s wort, and more. People drink them for sleep, digestion, immunity, or just because they taste good. But unlike prescription drugs, herbal teas aren’t tested for safety before they hit the shelf. The FDA treats them as food, not medicine. That means no required clinical trials, no standardized dosing, and no warning labels about interactions.

That’s a problem because many of these plants contain powerful compounds that interact with your body’s drug-processing systems. These interactions aren’t theoretical. They’ve been seen in real patients. A 2023 study found that drinking three cups of strong green tea daily cut the blood levels of the beta-blocker nadolol by 85%. That’s not a small drop-it’s enough to make the drug useless. And if your blood pressure spikes because the medication isn’t working, you could end up in the hospital.

Green Tea: The Silent Drug Thief

Green tea is one of the most popular herbal teas in the U.S., often consumed for its antioxidants. But its active ingredient, epigallocatechin gallate (EGCG), doesn’t just fight free radicals-it blocks the transporters your body uses to absorb certain medications.

Studies show green tea can reduce the effectiveness of:

• Atorvastatin (Lipitor): Blood levels drop by 31-39%
• Nadolol (Corgard): Bioavailability drops by up to 85%
• Simvastatin: Concentrations spike 2.3-fold due to P-glycoprotein inhibition, raising the risk of muscle damage
• Fluoroquinolone antibiotics (like ciprofloxacin): Absorption is blocked

These aren’t lab guesses. These are results from human trials. The mechanism? Green tea inhibits OATP1A1 and OATP1A2-proteins that help move drugs into your bloodstream. If those proteins are blocked, your medication doesn’t get absorbed. You’re paying for a drug that’s not working.

St. John’s Wort: The Mood Booster That Kills Other Medications

St. John’s wort is often used for mild depression. But it’s one of the most dangerous herbal teas when mixed with prescription drugs. It triggers enzymes in your liver-CYP3A4 and CYP2D6-that break down medications too fast. The result? Your drugs get flushed out before they can do their job.

Dr. Craig Hopp from the National Center for Complementary and Integrative Health says: “St. John’s wort speeds up processes that change the drug into inactive substances, leading to decreased drug levels in your body.”

That’s deadly with:

• Warfarin: Reduced effectiveness increases stroke risk
• Cyclosporine: Organ transplant patients can reject their new organ
• Birth control pills: Breakthrough bleeding and unintended pregnancy
• Antiretrovirals: HIV treatment fails
• Antidepressants: Risk of serotonin syndrome

Even if you’re not taking these drugs now, you might be soon. If you’re on St. John’s wort tea and your doctor prescribes a new medication, you need to speak up-before you take the first pill.

Chamomile, Hibiscus, and Blood Pressure

Chamomile tea is a bedtime staple. But it contains apigenin, a compound that can interfere with how your liver breaks down drugs. Early research suggests it might reduce the effectiveness of oral contraceptives and some antidepressants.

Hibiscus tea, on the other hand, is marketed for lowering blood pressure. And it works. But if you’re already taking lisinopril, enalapril, or another ACE inhibitor, hibiscus can push your blood pressure too low. There are documented cases of systolic pressure dropping below 90 mmHg-leading to dizziness, fainting, or even falls in older adults.

And it’s not just hibiscus. Licorice root tea can lower potassium levels, which is dangerous if you’re on diuretics or heart medications. Ginger and garlic teas can thin your blood. If you’re on warfarin, even small amounts can raise your INR and cause internal bleeding.

Who’s at the Highest Risk?

Not everyone who drinks herbal tea is in danger. But certain groups are at much higher risk:

• Older adults: 70% of adults over 65 use herbal supplements, but only 25% tell their doctors
• People on multiple medications: Polypharmacy increases interaction chances exponentially
• Patients with narrow therapeutic index drugs: These are medications where the difference between a helpful dose and a toxic one is tiny. Warfarin, digoxin, cyclosporine, lithium, and theophylline fall into this category. Even small changes in drug levels can be life-threatening
• People with kidney or liver disease: Their bodies can’t process herbs or drugs as efficiently

These aren’t edge cases. They’re common. In the U.S., over 40% of adults take at least one prescription drug. Nearly a quarter take herbal supplements. The overlap is huge-and mostly unmonitored.

What You Should Do Right Now

You don’t need to stop drinking herbal tea. But you need to be smart about it.

1. Make a list. Write down every herbal tea you drink, how often, and how much. Include blends with multiple herbs-many store-bought teas contain 5-10 ingredients you’ve never heard of.
2. Bring it to every doctor’s visit. Don’t wait for them to ask. Say: “I drink chamomile tea every night and green tea in the morning. Are these safe with my meds?”
3. Avoid herbal teas if you’re on warfarin, digoxin, cyclosporine, or theophylline. The risk isn’t worth it. Stick to plain water or decaf black tea.
4. Don’t assume “natural” means safe. The FDA has issued multiple warnings: “Natural does not mean safe.”
5. Watch for warning signs: Unusual bruising, dizziness, rapid heartbeat, confusion, or sudden changes in how you feel after starting a new tea. These could be signs of an interaction.

What Your Doctor Should Be Asking

Most doctors don’t ask about herbal teas because they assume patients won’t mention them. But patients don’t think of tea as a “supplement.” They think of it as a drink.

Healthcare providers need to ask directly: “Do you drink any herbal teas? Even just once a week?”

And they need to check for interactions using updated tools. The FDA and European Medicines Agency have both added interaction warnings for 17 common herbal teas. But many clinics still rely on outdated databases.

If your doctor doesn’t know about hibiscus and lisinopril interactions-or green tea and nadolol-it’s up to you to bring the information. Print out a simple list. Show it to them. Your life might depend on it.

The Bigger Picture

The herbal tea market is booming. It’s projected to hit $11 billion by 2027. Companies are marketing blends for “heart health,” “liver detox,” and “immune support.” But none of these claims are reviewed by the FDA. And none of them come with interaction warnings.

Meanwhile, the number of Americans taking five or more prescription drugs is rising. Older adults are drinking herbal teas to feel better. But they’re not telling anyone. That’s a recipe for disaster.

The science is still catching up. Only 17% of known herb-drug interactions have been confirmed in human trials. That means there are probably dozens more we don’t know about yet. But we know enough to be cautious.

You don’t have to give up your tea. But you do have to be informed. Your medications are carefully dosed for a reason. Herbal teas can change that balance-and you won’t always feel it until it’s too late.