NEW YORK, July 19: For many people, a day isn’t complete without coffee. It’s energizing and widely enjoyed worldwide. However, caffeine in coffee can interfere with some medicines, affecting how well they work or causing unwanted side effects. Tea also contains caffeine but usually in smaller amounts, so its impact differs.

Here’s what you need to know about coffee’s effects on common medications—and how to use them safely.

Caffeine is a stimulant, as is pseudoephedrine, a common decongestant in cold remedies like Sudafed. When taken together, they can amplify side effects such as jitters, headaches, rapid heartbeat, insomnia, and restlessness. Some cold medicines already contain caffeine, increasing these risks.

Studies also show that combining caffeine and pseudoephedrine can raise blood sugar and body temperature, which is especially important for people with diabetes. Similar concerns exist for ADHD medications like amphetamines and asthma drugs such as theophylline, which share chemical similarities with caffeine.

Levothyroxine, used for underactive thyroid, is sensitive to timing. Drinking coffee too soon after taking it can reduce absorption by up to 50%. Caffeine speeds up digestion, giving the drug less time to be absorbed, and may bind to it in the stomach. This means less medication reaches the bloodstream, potentially causing hypothyroid symptoms like fatigue and weight gain to return.

The same caution applies to osteoporosis drugs like alendronate and risedronate, which need to be taken on an empty stomach, with a 30-60 minute wait before eating or drinking.

Caffeine’s interaction with mental health medications can be complex. SSRIs (like sertraline and citalopram) may have reduced absorption due to caffeine binding in the stomach. Older antidepressants, tricyclic antidepressants (TCAs) such as amitriptyline, are broken down by the same liver enzyme that processes caffeine (CYP1A2). This can slow drug metabolism, increasing side effects or prolonging caffeine’s effects, leading to jitteriness.

Clozapine, an antipsychotic metabolized by CYP1A2, can have its blood levels nearly doubled by drinking 2-3 cups of coffee, raising risks of drowsiness, confusion, or serious complications.

Some over-the-counter painkillers contain caffeine to speed absorption and enhance effectiveness. Coffee can make the stomach more acidic and empty faster, helping drugs like aspirin absorb quicker. While this might help relieve pain sooner, it can also increase side effects like stomach irritation or bleeding, especially combined with other caffeine sources. Although serious cases are rare, caution is advised.

Caffeine can temporarily raise blood pressure and heart rate for a few hours after consumption. For people on blood pressure medications or drugs for irregular heart rhythms, caffeine might reduce their effectiveness. This doesn’t mean heart patients must avoid coffee entirely, but they should monitor their symptoms and consider limiting caffeine or switching to decaf if needed.

How to stay safe

Coffee is more than just a comforting ritual; it’s a powerful chemical that can affect how your medicines work. To avoid problems:

When in doubt, ask your pharmacist or doctor whether your medicine and coffee make a safe pair. A quick chat can help you avoid side effects and enjoy your coffee worry-free.