Adenosine – Hospitals use adenosine to regulate unstable or irregular heart rhythms; green tea can inhibit its stabilizing effects.
Antibiotics, Beta-lactam – Green tea can essentially make beta-lactam antibiotics more effective; it can help reduce bacterial resistance to treatment
Benzodiazepines – Drugs like diazepam, lorazepam, and other medications often used to treat anxiety fall under the benzodiazepine family. Caffeine, like that found in green tea, can decrease the sedative-effects of these medications.
Beta-blockers, Propranolol, and Metoprolol – In general, caffeine can increase blood pressure in people taking blood pressure and heart disease meds like these.
Blood Thinning Medications (Including Aspirin) – The Vitamin K found in green tea makes blood thinning meds ineffective; green tea is also a no-no with aspirin in general because they both prevent the clotting of platelets, and when combined, can increase risk of bleeding.
Chemotherapy – Studies haven’t yet been conducted on humans, but some research suggests green tea can help increase the effectiveness of chemo meds (i.e., doxorubicin and tamoxifen). It is also suggested, however, that green and black tea can stimulate a gene in prostate cancer cells that make them stronger against the chemotherapy. In other words, prostate cancer patients should avoid both black and green tea while receiving chemotherapy.
Clozapine – If drinking green tea, wait at least 40 minutes before taking clozapine in order to preserve the anti-psychotic effects of this medication.
Ephedrine – Green tea mixed with ephedrine can cause insomnia, tremors, agitation, and weight loss.
Lithium – Used to treat manic depression, lithium’s levels in the blood can be reduced by green tea.
Monoamine Oxidase Inhibitors (MAOIs) – MAOIs, like phenelzine and tranylcypromine, are used to treat depression. Combining them with green tea can cause a hypertensive crisis, or severe increase in blood pressure.
Oral Contraceptives – Stimulating effects of green tea may be prolonged when combined with oral contraceptives, which tend to extend the amount of time caffeine stays in the body.
Phenylpropanolamine – In 2000, the FDA urged manufacturers to remove this longtime ingredient in over-the-counter and prescription cold and cough meds and weight loss products from the market. When phenylpropanolamine is combined with caffeine, the results may include mania and severe increase in blood pressure.