How Your Meds Interact With Your Diet
AIIM Pharmacist Bryan Spencer discusses food and Rx and how they can interact.
Grapefruit gets most of the attention, but your daily tea, coffee, and even cola can also change how well your medications work. These everyday beverages interact with drugs through two main pathways: caffeine competes with certain drugs for the same liver enzyme, while the natural compounds in tea block the "doorways" (transporters) that let drugs into your bloodstream. Here is what the science shows.
Green tea: often lowers drug absorption
Green tea (Camellia sinensis) is one of the most studied. A 2025 clinical review found that in most human studies, drinking green tea decreased the amount of drug that reached the bloodstream, by anywhere from 18% to 99% (Kyriacou et al., Clinical Pharmacology & Therapeutics, 2025). Affected medications included the cholesterol drugs atorvastatin and rosuvastatin, the heart medications nadolol and celiprolol, and the allergy drug fexofenadine.
The mechanism is mostly in the gut: green tea compounds called catechins (especially EGCG) block uptake transporters (called OATP) that normally pull drugs into the body, and the tannins can bind drugs directly. Green tea tannins can also reduce absorption of iron, making it less effective for treating anemia. Because nadolol levels can drop substantially, people taking it for blood pressure should be especially cautious.
Coffee and caffeine: can raise drug levels
Caffeine works the opposite way. It is broken down by a liver enzyme called CYP1A2, the same enzyme that processes many medications. When you drink coffee with these drugs, they compete, and drug levels can rise (van Dam et al., New England Journal of Medicine, 2020).
Documented examples include the antipsychotic clozapine (levels up to roughly doubled), as well as theophylline, lithium, and the sleep aids melatonin and zolpidem (Belayneh & Molla, BioMed Research International, 2020). Among antidepressants, the ones most affected are those cleared by CYP1A2, including fluvoxamine, duloxetine, mirtazapine, trazodone, clomipramine and imipramine (Spina & de Leon, Journal of Neural Transmission, 2015). Caffeine can also add to the effects and toxicity of stimulants, including amphetamines, methylphenidate and pseudoephedrine, raising the risk of high heart rate, elevated body temperature, and (with amphetamine-type drugs such as MDMA) dangerous overheating (Kennedy & Wightman, Sports Medicine, 2022; Vanattou-Saïfoudine et al., British Journal of Pharmacology, 2012). Caffeine may also increase bleeding risk when combined with warfarin.
Cola and energy drinks
Caffeinated cola drinks share caffeine's effects and are also acidic, which can change how some drugs dissolve. Reports link cola consumption to increased levels of methotrexate, carbamazepine, and phenytoin, and to reduced effectiveness of lithium and warfarin (Nomani et al., Clinical Nutrition, 2019).
Herbal teas
"Caffeine-free" does not mean interaction-free. Chamomile tea can inhibit the CYP3A4 enzyme; a case report described elevated levels of the transplant drug cyclosporine in someone drinking it regularly (Bertuccioli et al., Journal of Medicinal Food, 2022). Chamomile, valerian, and kava also have sedative effects that can add to those of opioids or sleep medications. Rooibos tea inhibits several CYP enzymes in laboratory testing (Fantoukh et al., Journal of Agricultural and Food Chemistry, 2019).
The bottom line
If you take a medication with a "narrow safety window," such as warfarin, lithium, clozapine, thyroid medication, or transplant drugs, talk with your pharmacist or doctor before making tea, coffee, or herbal infusions a daily habit. Keeping your intake consistent and separating tea from medications by a couple of hours can help, but personalized advice is always best.