7 medications that may interact with green tea

People use green tea, either as a beverage or supplement, to support cholesterol, promote weight loss, and for other potential health benefits. But even natural products like green tea can interact with medications, so it’s important to know which medications to watch out for.

1. Warfarin

Warfarin, a blood thinner, may interact with green tea:

• Why it matters: Green tea contains vitamin K, which may affect how warfarin works. Warfarin is known as a narrow therapeutic index drug. This means that the difference between an effective dose and a dangerous dose is very narrow. When taking warfarin, it is generally advisable to maintain a consistent intake of vitamin K.
• What could happen: Drinking green tea may cause changes in your international normalized ratio (INR), a measure of the time it takes for your blood to clot. This could make warfarin either less effective (and increasing your risk of blood clots) or too strong (increasing your risk of bleeding).
• What to do: If you consume green tea, either in your diet or as a supplement, consult your healthcare professional before combining it with warfarin. People who take warfarin are monitored very closely to make sure their INR stays within a safe and effective range.

2. Nadolol

Another drug that may interact with green tea is Nadolol, a beta blocker:

• Why it matters: Nadolol is generally used to treat hypertension (high blood pressure) and prevent angina (chest pain).
• What could happen: Large amounts of green tea may make nadolol less effective. In one study, drinking 700 milliliters (mL) per day of green tea for two weeks reduced the amount of nadolol in the blood by about 85%, making it much less effective in controlling blood pressure and/or chest pain.
• What to do: If you are taking nadolol, consult your healthcare professional before using or drinking green tea.

3. Statins

Statins, a type of medication used to treat high cholesterol, may potentially interact with green tea:

• Why it matters: Statins are the most widely prescribed type of cholesterol-lowering medication.
• What could happen: Green tea may lower levels of the statin Lipitor (atorvastatin) by reducing its absorption by approximately 25%, which may reduce its effectiveness. Some data suggest that this type of interaction might also occur with the statins Crestor (rosuvastatin) and Zocor (simvastatin).
• What to do: If you are taking a statin, check with your healthcare professional about the safe consumption of green tea.

4. Evista (Raloxifene)

Research has shown that green tea may interact with raloxifene, although how this interaction occurs is not fully understood:

• Why it matters: Evista (raloxifene) is a medicine commonly used to prevent and treat osteoporosis (a disease that weakens bones). It is also used to reduce the risk of developing invasive breast cancer.
• What could happen: Drinking green tea while using raloxifene may reduce the absorption of raloxifene, which may affect its effectiveness.
• What to do: If you are taking raloxifene, consult your healthcare professional before consuming green tea or using green tea supplements.

5. Velcade (bortezomib)

Velcade (bortezomib), a type of targeted cancer treatment, has been shown to interact with green tea:

• Why it matters: Velcade (bortezomib) is a medicine used to treat certain types of cancers, including multiple myeloma and mantle cell lymphoma.
• What could happen: Green tea may make this medication less effective by stopping it from killing cancer cells.
• What to do: It is recommended to avoid consuming green tea during treatment with bortezomib. Check with your healthcare professional for more information and personalized medical advice.

6. Tacrolimus

Tacrolimus (known by the brand names Prograf, Astagraf XL and Envarsus XR) is an immunosuppressant that may also interact with green tea:

• Why it matters: Tacrolimus is commonly used to prevent organ rejection after transplantation. Like warfarin, it is a drug with a narrow therapeutic index.
• What could happen: There have been reports of green tea interacting with tacrolimus, potentially resulting in elevated tacrolimus levels and increased suppression of the immune system, which could lead to serious side effects.
• What to do: If you are taking tacrolimus, consult your healthcare professional before adding green tea to your diet.

7. Sildenafil

Research has suggested that sildenafil (brand names Viagra and Revatio) may interact with green tea:

• Why it matters: Sildenafil is commonly used to treat erectile dysfunction (the inability to get or maintain an erection) as well as pulmonary hypertension (high blood pressure in the arteries of the lungs).
• What could happen: Some research has shown that green tea increases sildenafil levels in the body, which could potentially lead to more serious side effects, such as dizziness, headaches, flushing, or prolonged, painful erections.
• What to do: Check with your healthcare professional before combining green tea and sildenafil.