4 Ways Caffeine Can Impact Your Medications, According to Dietitians

Caffeine is an essential part of many people’s daily routines. Whether in the form of a morning cup of coffee, an afternoon pick-me-up or a soda with dinner, caffeine is a widely consumed stimulant that can impact your body in various ways.

Alongside its energizing qualities, caffeine has a complex relationship with medications that shouldn’t be overlooked. Understanding how caffeine interacts with certain medications is critical for managing your health effectively and avoiding potential complications. Here, we’ll cover caffeine’s impact on certain medications, discuss its potential risks and side effects, and provide expert guidance for safe caffeine consumption. Keep reading to learn more.

What Is Caffeine?

Caffeine is a natural stimulant that belongs to a class of compounds called xanthines, and it's the most widely consumed psychoactive drug in the world. It’s most commonly found in coffee beans, tea leaves, cacao beans and kola nuts. Caffeine is also added to many common beverages and supplements, like energy drinks, sodas and pre-workout supplements.

Drinking caffeine works on your brain to keep you awake and alert, pushing back feelings of tiredness. It can help you feel more focused, stay more alert and even perform better physically, which is why so many people turn to it for a quick pick-me-up. However, caffeine should be consumed in moderation, as too much can lead to adverse effects such as restlessness, anxiety and insomnia.

Lauren Harris-Pincus, M.S., RDN, an author and founder of NutritionStarringYOU.com, tells EatingWell, “Caffeine is the most commonly consumed central nervous system stimulant. It can impact memory, learning and performance by keeping you alert and less fatigued. Caffeine is most commonly found in coffee, tea, cola and cocoa, as well as in guarana and yerba mate.”

4 Ways Caffeine Can Impact Your Medications

While caffeine is a widely beloved stimulant touted for its energizing effects and health benefits, Harris-Pincus cautions that caffeine’s positive qualities may be influenced when combined with certain drugs or medications, stating, “Caffeine may increase or decrease the effectiveness of certain medications, depending on how the drugs are metabolized.”

1. May Increase Bleeding Risk with Blood Thinners

Caffeine can interact with blood thinners like warfarin (Coumadin) and increase the risk of bleeding, cautions Harris-Pincus. Warfarin works by inhibiting the activity of vitamin K, which is crucial for blood clotting. Caffeine can interfere with the metabolism of warfarin, potentially causing blood thinning and increasing the risk of bleeding, according to research.

2. Could Reduce Thyroid Medication Absorption

Harris-Pincus says that caffeine consumption can interfere with the absorption of certain thyroid medications, such as levothyroxine (Synthroid), used to treat hypothyroidism. Caffeine may reduce the absorption of levothyroxine in the gastrointestinal tract, leading to reduced effectiveness, suggests a 2022 study.

3. May Intensify ADHD Medication Effects

Medications like methylphenidate (Ritalin) and amphetamine (Adderall) are commonly prescribed to help improve focus and concentration in those with attention deficit/hyperactivity disorder. However, caffeine can interact with these medications and may increase their stimulant effects. “Meds for ADHD, such as Adderall and Ritalin, combined with caffeine can increase feelings of anxiety, insomnia, jitters and potential heart problems,” says Harris-Pincus.

4. Could Alter Estrogen Levels with Oral Contraceptives

According to the National Institutes of Health, caffeine can interact with oral contraceptives and impact how your body metabolizes estrogen. Some studies suggest that caffeine may increase estrogen levels in women taking oral contraceptives. Harris-Pincus tells us, “Oral contraceptives can inhibit the enzyme responsible for breaking down caffeine so that you may feel prolonged or more significant effects.”

Related: What Happens to Your Body When You Drink Coffee Every Day

Who Should Avoid Caffeine?

Those who are pregnant should limit their caffeine intake, as it may raise the risk of miscarriage, premature birth and other pregnancy complications, according to a 2023 review. If you have anxiety or panic attacks, caffeine might make things worse by making you feel more nervous or jittery. Additionally, if you have certain heart issues, high blood pressure, or gastroesophageal reflux disease (GERD), caffeine could potentially worsen your symptoms.

“Those with high blood pressure, heart arrhythmias, gastroesophageal reflux, migraines, sleep disorders, taking certain medications or are pregnant or breastfeeding should speak with their doctor about how much caffeine is advisable for them to consume,” says Harris-Pincus.

Related: What Happens to Your Body When You Drink Coffee During Your Menstrual Cycle

Side Effects of Caffeine Supplements

Common side effects of caffeine supplements include jitteriness, nervousness, restlessness and increased heart rate. Some people may also experience gastrointestinal issues such as stomach upset, diarrhea or acid reflux. In some cases, consuming large amounts of caffeine can lead to caffeine overdose, also known as caffeine toxicity. Symptoms of caffeine overdose include dizziness, rapid or irregular heartbeat, anxiety, fever and nausea.

“Some people are sensitive to caffeine and may experience unpleasant side effects like jitters, nausea, an increase in heart rate and blood pressure, trouble sleeping or anxiety,” says Harris-Pincus.

How Much Caffeine per Day Is Safe?

While there’s no specific daily recommended intake for caffeine, the NIH states that doses of up to 400 milligrams a day are considered safe. However, caffeine sensitivity can vary widely depending on factors such as age, sex and weight. Some people may experience side effects at lower doses, while others may tolerate higher amounts without issue.

“The consensus is to limit total caffeine intake to 400 milligrams per day for adults, assuming you are not sensitive to its stimulant effects. An 8-ounce cup of coffee can contain anywhere from 95 to 200 milligrams of caffeine, a can of cola has around 40 milligrams, and a cup of tea contains 14 to 60 milligrams,” says Harris-Pincus.

Related: How Much Caffeine Is Too Much? Here's What a Dietitian Has to Say

The Bottom Line

Caffeine is one of the world's most widely consumed and enjoyed dietary compounds. However, caffeine can interact with certain medications. Being aware of these interactions is essential, as they can impact the effectiveness and safety of your medical treatment. Caffeine may affect the absorption, metabolism or side effects of certain medications, including blood thinners, oral contraceptives and medications for the thyroid and ADHD. If you’re taking any medications, speak with your health care provider or pharmacist about how caffeine may interact with your medication regimen. If you need to limit your caffeine intake, there are many other beverages and foods you can enjoy instead, such as herbal teas, decaffeinated coffee or caffeine-free soft drinks.