Your morning coffee might seem harmless, but caffeine can interfere with how some medications work, either reducing their effectiveness or increasing the risk of side effects. Combining coffee with cold and flu medications can increase stimulant effects, leading to jitteriness, insomnia, or a racing heart, especially if the medications already contain caffeine. Taking thyroid medication like levothyroxine with coffee can speed up digestion, reducing the absorption of the drug by up to 50%. Some antidepressants and antipsychotics compete with caffeine in the liver, slowing metabolism or raising drug absorption, sometimes dramatically. Caffeine may speed up how fast painkillers like aspirin work, but it can also increase the risk of stomach irritation or bleeding when combined. Coffee temporarily raises heart rate and blood pressure, which can counteract medications for heart conditions like arrhythmias or hypertension. To stay safe, talk to your doctor or pharmacist. A quick check-in can help you avoid side effects and get some peace of mind.