Caffeine, found in coffee and tea, is broken down in the liver by an enzyme called CYP1A2. Some medications also rely on this enzyme for processing, and they can compete with caffeine. This is particularly important for a drug called clozapine, which is used to treat schizophrenia. Caffeine can slow down how the body processes clozapine, which can make its effects—both helpful and harmful—stronger. If someone suddenly stops drinking caffeine, the body might start processing clozapine more quickly, which can lead to a sudden worsening of psychotic symptoms. Caffeine can also affect how the body handles lithium, a medication used to treat bipolar disorder. It helps the body get rid of lithium through urine, which can lower the amount of lithium in the blood. If someone stops consuming caffeine suddenly, lithium levels might rise, which can be dangerous. Therefore, people taking lithium or clozapine should inform their doctor if they change how much caffeine they consume, as this may require adjusting their medication dose. On the other hand, certain medications, such as ciprofloxacin, norfloxacin, and fluvoxamine, can slow down the breakdown of caffeine in the body. This can lead to higher levels of caffeine in the blood, increasing the risk of side effects like restlessness, trouble sleeping, nausea, heart palpitations, and sweating, especially in people who drink a lot of coffee or tea. Patients taking these medications should be informed about the need to limit their caffeine intake. This advice also applies to people taking theophylline, a drug similar to caffeine used for respiratory conditions. In addition to caffeine, tea contains compounds called tannins, which can bind to iron and reduce how much of it is absorbed from the digestive tract. For this reason, it is recommended that people taking iron supplements should avoid drinking tea around the time they take their medication to ensure proper absorption. Sources: "Foods, beverages, tobacco, health and medications," Health Insurance, October 2025; public medication database; drug interaction thesaurus, National Agency for the Safety of Medicines and Health Products.