How Coffee Can Affect Your Medications – What Science and Experts Say

Coffee is a beloved daily ritual for millions, but few realize it may interfere with medications ranging from thyroid pills to antidepressants. According to a detailed report by Dipa Kamdar, Senior Lecturer in Pharmacy Practice at Kingston University and published by The Conversation UK on May 30, 2025, caffeine can alter how drugs are absorbed and metabolized in the body—potentially reducing effectiveness or increasing side-effects. Here’s what every coffee drinker should know to stay safe while on medication.

For many people, the day doesn’t officially begin until that first sip of coffee. It’s energizing, comforting, and consumed by billions worldwide. However, new insights from Dipa Kamdar, Senior Lecturer in Pharmacy Practice at Kingston University, highlight a critical but often overlooked concern: coffee may interfere with the way certain medications work in the body.

The report, published by The Conversation UK, underscores that while caffeine boosts energy, it can also amplify side-effects, reduce drug absorption, and affect how long medications stay active in the system. Here’s a closer look at the main interactions and what you can do to avoid complications.

1. Cold and Flu Medications

Many cold remedies, such as those containing pseudoephedrine (e.g., Sudafed), are stimulants—just like caffeine. When taken together, these stimulants may cause restlessness, insomnia, headaches, rapid heartbeat, and even increased blood sugar and body temperature, especially for people with diabetes.

Caffeine can also intensify the side effects of asthma medications like theophylline and ADHD treatments such as amphetamines, potentially leading to jitteriness or disrupted sleep.

2. Thyroid Medications

If you’re taking levothyroxine for hypothyroidism, coffee timing matters. Studies show that drinking coffee within an hour of taking the pill can reduce its absorption by up to 50%, leading to decreased effectiveness and the return of symptoms such as fatigue or weight gain.

This interaction is mainly seen with tablet forms of the drug. To ensure maximum effectiveness, levothyroxine should be taken on an empty stomach with water, followed by a 30–60 minute wait before consuming coffee or food.

This rule also applies to osteoporosis medications like alendronate and risedronate (bisphosphonates), which also require an empty stomach to be absorbed properly.

3. Antidepressants and Antipsychotics

The interaction between caffeine and mental health medications is complex. For example:

• SSRIs (sertraline, citalopram): Lab studies suggest that caffeine may bind to these drugs in the stomach, potentially reducing their absorption and effectiveness.

• Tricyclic antidepressants (TCAs) like amitriptyline and imipramine: These drugs and caffeine are metabolized by the same liver enzyme (CYP1A2), which can lead to slower drug breakdown and increased side-effects or prolonged caffeine stimulation.

• Clozapine, a powerful antipsychotic, is also broken down by CYP1A2. Studies reveal that drinking just 2–3 cups of coffee can raise clozapine levels by up to 97%, increasing risks of drowsiness, confusion, or even more serious health issues.

4. Painkillers

Some over-the-counter pain medications (e.g., aspirin, paracetamol) include added caffeine to speed up absorption. Coffee may enhance this effect by increasing stomach acidity and emptying speed.

While this might help the drug work faster, it could also increase the risk of stomach irritation or bleeding, especially when multiple sources of caffeine are consumed.

5. Heart Medications

Caffeine can raise blood pressure and heart rate for several hours after consumption. This could counteract the benefits of medications prescribed for hypertension or arrhythmia. While patients with heart conditions don’t necessarily need to give up coffee entirely, monitoring intake and opting for decaffeinated coffee may be advisable in some cases.

Practical Tips to Stay Safe

To enjoy coffee while staying safe on your medications, consider the following expert recommendations:

• Take levothyroxine and bisphosphonates on an empty stomach with water, and wait at least 30–60 minutes before consuming coffee or food.

• Be mindful when using cold/flu medications, ADHD drugs, and asthma treatments alongside caffeine, as stimulant effects may be amplified.

• If you are on antidepressants, antipsychotics, or heart medications, discuss your caffeine habits with your doctor to adjust dosages or timing if needed.

• Watch for signs like insomnia, jitteriness, or heart palpitations — these could be clues that caffeine is affecting your medication.

• Metabolism varies: some people handle caffeine better than others. If you feel off after your coffee, consult your doctor or pharmacist.

Final Thoughts

Coffee is a powerful beverage that goes beyond flavor and energy—it’s a bioactive compound capable of altering the effects of several medications. While most people can still enjoy their daily brew, timing, dosage, and personal sensitivity matter.

As Dipa Kamdar emphasizes in her article for The Conversation UK, “A short conversation with your pharmacist or doctor might save you weeks of side-effects or reduced treatment effectiveness – and help you enjoy your brew with peace of mind.”