Coffee is one of the most widely consumed beverages in the world. The main component in coffee is caffeine, also found in other beverages such as tea, sodas, and energy drinks. 

Many people consume caffeine to improve performance and enhance mental alertness and memory. It is also used for health conditions like migraine or severe headache, ADHD, asthma, gallbladder disease, low blood pressure, and depression. Some studies have shown that caffeine protects brain cells and may reduce the risk of Alzheimer’s disease and Parkinson's disease.

Yet, caffeine intake can affect many over-the-counter and prescription drugs and lead to significant drug interactions. 

In this article, we will take a look at some caffeine-drug interactions. The goal is to help you understand how coffee consumption can affect your medications and which medications can interact with caffeine. 

What does caffeine do to the body?

Caffeine is a central nervous system stimulant. It crosses the blood-brain barrier and increases brain activity. It also leads to a slight increase in cortisol (the body’s primary stress hormone) and adrenaline blood levels. This is why many people feel more alert, focused, and refreshed after caffeine intake. 

Caffeine also affects other organ systems. For example, it can increase gastric acid secretion, raise blood pressure, and cause muscle twitching. In addition to that, caffeine is considered a mild diuretic; caffeine causes the kidneys to not reabsorb water, leading to increased urination.

Caffeine can have serious cardiovascular effects at larger doses, including heart rhythm abnormalities. With chronic use and large intakes of caffeine, it does carry a slight risk of bone mineral density reduction (bone thinning). 

How much dietary caffeine consumption is safe?

The U.S. Food and Drug Administration considers a daily intake of 400 mg of caffeine as safe for healthy adults. That’s roughly four cups of brewed coffee, 10 cans of soda, or two shots of energy drinks. It’s important to check the labels of caffeine-containing beverages since the caffeine content from different brands can vary widely. 

Why do caffeinated beverages affect drugs?

Studies have shown that caffeine consumption can affect the absorption, distribution, metabolism (breakdown), and elimination of many drugs. 

Caffeine interactions with medications can potentially increase the side effects of the drugs, leading to toxicity, or reducing the effectiveness of the drug therapy

For example, diuretic drugs (water pills) decrease potassium, and caffeine decreases potassium, so taking them together can lead to low blood potassium levels. 

That’s why it’s important to follow your doctor and pharmacist’s instructions on appropriate caffeine consumption while taking certain prescription drugs.

Caffeine Interactions with Medications

Here are some examples of medications with known caffeine-drug interactions. 

Ephedrine and Caffeine

Ephedrine is a stimulant drug used to treat allergic reactions and asthma. It is also used to treat hypotension (low blood pressure) under anesthesia. 

Since caffeine and ephedrine are stimulants, taking them together can lead to serious side effects, including increased heart rate, high blood pressure, and heart problems in the long run. 

Other drugs that can produce similar caffeine effects are stimulants like amphetamines and cocaine. 

Cardiac Drugs and Caffeine

Adenosine (Adenocard) and dipyridamole (Persantine) are prescription drugs used during cardiac stress testing. Adenosine is also used to treat certain types of heart arrhythmias. Persantine is used, along with other blood thinners, to prevent blood clot formation in patients who have undergone heart valve replacement. 

Caffeine can block the actions of adenosine and dipyridamole and make them less effective. Because of these drug interactions, your doctor may instruct you to stop coffee consumption and other caffeine-containing products 24 hours before a cardiac stress test. 

Caffeine Interactions with Anti-Seizure Medications

Caffeine can lower the effect of certain medications used to treat seizures. This can lead to an increase in seizures in some people. Examples of seizure medications that may be less effective with caffeine include:

• Carbamazepine (Tegretol)
• Ethosuximide (Zarontin)
• Felbamate (Felbatol)
• Phenobarbital (Luminal)
• Phenytoin (Dilantin)
• Valproate 
   

Caffeine Effects on Anticoagulants and Antiplatelet Drugs

Anticoagulants and antiplatelet drugs, also called blood thinners, reduce the risk of blood clotting. Caffeine can prevent the breakdown of anticoagulants like warfarin and increase blood levels of these drugs, leading to increased bleeding risk. Therefore, taking caffeine with anticoagulants can slow blood clotting and increase the risk of bruising and bleeding. 

Drug Interactions that Reduce Elimination of Caffeine

Drug interactions with certain medications can affect the metabolism of caffeine in the body, i.e., how quickly it is broken down and eliminated. Taking these medications with caffeine can increase the “caffeine buzz” you experience. It can also lead to an increased risk of side effects like headache, jitteriness, irritability, hyperactivity, and increased heart rate. 

Examples of medications that can cause an intensified effect of caffeine include:

• Quinolone antibiotics such as levofloxacin (Levaquin), ciprofloxacin (Cipro), and moxifloxacin (Avelox) 
• Cimetidine (Tagamet)
• Disulfiram (Antabuse)
• Estrogens such as in birth control pills
• Antidepressants like fluvoxamine (Luvox) 
• Verapamil (Calan) is used to treat high blood pressure, angina (chest pain), and irregular heartbeat

Effects of Caffeine on Drug Absorption

Caffeine increases gastric acid secretion and can lead to a decrease in gastric pH and changes in gastrointestinal function. This can affect the absorption of certain medications. 

For example, drinking 2-3 cups of coffee can reduce midazolam absorption by 75% (this medication is used for sedation during anesthesia). On the other hand, drinking 2 cups of coffee with a 650-mg dose of aspirin can significantly increase aspirin's absorption.

Other medications whose absorption and bioavailability can be affected by caffeine include:

• Antipsychotic medications such as phenothiazine and chlorpromazine
• Halofantrine (antimalarial)
• Ergotamine used for migraine treatment

Increased Side Effects Due To Caffeine-Drug Interactions

Caffeine consumption can decrease how quickly the body breaks down and eliminates certain medications. This can increase the medicine's effects and increase the risk of side effects. Examples of drugs that can have enhanced effects and more side effects with caffeine include:

• Clozapine (Clozaril), an antipsychotic medication
• Lithium, a mood stabilizer used to treat patients with bipolar disorder
• Antidepressants called MAOIs, such as phenelzine (Nardil), tranylcypromine (Parnate), and selegiline (Zelapar).
• Riluzole (Rilutek), a drug used in ALS patients
• Theophylline, a medication used to treat shortness of breath and wheezing caused by lung diseases
• Flutamide (Eulexin), a drug used to treat prostate cancer

Wrapping Up

There is no harm in drinking caffeinated beverages in moderation. Doctors advise limiting caffeine consumption to 400 mg per day or less, equivalent to four cups of brewed coffee. 

Some medications should not be taken with caffeine. Interactions between caffeinated beverages and prescription drugs can lead to potentially dangerous effects, such as making the drugs less effective, making your conditions worse, increasing your risk of side effects, or increasing the stimulant effects of caffeine. 

If you are not sure whether there is a drug interaction between your prescription drug and caffeine, ask your healthcare provider or pharmacist for further drug information. Make sure you follow their instructions to avoid caffeine or reduce its intake with certain medications. 

References:

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7397437/