If you are currently being treated with any of the following medications, you
should not drink green tea or take green tea extract without first talking to
your healthcare provider:
Green tea may inhibit the actions of adenosine, a
medication administered in a hospital setting for an irregular (and usually
unstable) heart rhythm.
Green tea may increase the
effectiveness of beta-lactam antibiotics by reducing bacterial resistance to
Caffeine (including caffeine from green tea)
has been shown to reduce the sedative effects of benzodiazepines (medications
commonly used to treat anxiety, such as diazepam and lorazepam).
Beta-blockers, propranolol and metoprolol
caffeine from green tea) may increase blood pressure in people taking
propranolol and metoprolol (medications used to treat high blood pressure and
Blood Thinning Medications
Green tea should not be taken with
warfarin, a blood-thinning medication, because the herb contains vitamin K and,
thus, can render warfarin ineffective.
Similarly, green tea and aspirin should not be mixed because they both
prevent platelets from clotting. Using the two together, therefore, may increase
your risk of bleeding.
The combination of green tea and chemotherapy
medications, specifically doxorubicin and tamoxifen, increased the effectiveness
of these medications in laboratory tests. These results have not yet been
demonstrated in studies of people, however.
On the other hand, there have been reports of both green and black tea
extracts stimulating a gene in prostate cancer cells that may cause them to be
less sensitive to chemotherapy drugs. Given this potential interaction, black
and green tea (as well as extracts of these teas) should not be taken while
receiving chemotherapy for prostate cancer in particular.
The anti-psychotic effects of the medication
clozapine may be reduced if taken less than 40 minutes after drinking green tea.
When taken together with ephedrine, green tea may
cause agitation, tremors, insomnia, and weight loss.
Green tea has been shown to reduce blood levels of
lithium (a medication used to treat manic/depression).
Monoamine oxidase inhibitors (MAOIs)
Green tea may cause a
severe increase in blood pressure (called a "hypertensive crisis") when taken
together with MAOIs used to treat depression. Examples of MAOIs include
phenelzine and tranylcypromine.
Oral contraceptives can prolong the amount
of time caffeine stays in the body and may increase its stimulating effects.
A combination of caffeine (including
caffeine from green tea) and phenylpropanolamine (an ingredient used in many
over-the-counter and prescription cough and cold medications and weight loss
products)can cause mania and a severe increase in blood pressure. The FDA issued
a public health advisory in November 2000 to warn people of the risk of bleeding
in the brain from use of this medication and has strongly urged all
manufacturers of this drug to remove it from the market.