by Hellwig J

Drug Interactions: What You Need to Know

IMAGE You might know that certain prescription medications can interact with one another and cause potentially harmful side effects. But did you know that interactions can occur not only with prescription medications, but also with over-the-counter medications, supplements, and foods and beverages? Medications can even interact with diseases or conditions you may have. Fortunately, with a little careful planning, you can avoid serious drug interactions.

Types of Drug Interactions

There are 3 basic types of drug interactions:

Drug-Drug Interactions

These occur when one drug interferes with another drug, affecting how one or both act in or are eliminated from the body. These interactions can occur between prescription drugs, over-the-counter drugs, and even herbal or other dietary supplements, including vitamins. For example, vitamin E and aspirin both act to thin the blood. Taking these together could cause excessive bleeding. And combining antidepressants with the pain medication tramadol could cause seizures.
It is particularly important to remember that herbal products, which many people regard as natural alternatives to drugs, still behave like drugs in the body. For example, the herb called St. John’s wort can reduce blood levels of certain medications. Furthermore, if a person is already taking St. John’s wort along with another drug, stopping the herb may cause drug levels to rise, potentially leading to dangerous complications.

Drug-Food/Beverage Interactions

Drug-food/beverage interactions occur when a prescription or over-the-counter medication interacts with food or beverages. For example, taking the antibiotic tetracycline with a glass of milk can lessen the absorption of the antibiotic in the body and make it less effective. Grapefruit juice can block enzymes that metabolize numerous drugs, including some blood pressure-lowering drugs, anti-depressants, antihistamines, and the drug cyclosporine, thereby increasing blood levels of these drugs. Toxicity could result.

Drug-Condition Interactions

These occur when a prescription or over-the-counter medication interacts with a disease or condition. For example, decongestants, such as those found in many over-the-counter cold remedies, can cause an increase in blood pressure, which could be dangerous for people who already have high blood pressure.

Symptoms of Drug Interactions

The most common symptoms of drug interactions tend to be less serious and include the following:
  • Nausea
  • Headache
  • Heartburn
  • Lightheadedness
More serious—but less common—symptoms and results of drug interactions include the following:
  • Sharp increase or decrease in blood pressure
  • Irregular heartbeat
  • Buildup of toxins that could damage vital organs, such as the liver or heart
Consult your doctor or pharmacist if you experience any unusual side effect after taking a medication, no matter how mild or severe.

How to Avoid Drug Interactions

The key to avoiding drug interactions is to become informed about the potential interactions between all the drugs and dietary supplements you take by talking with your doctor and pharmacist.
Some steps you can take include:
  • Read the labels of all over-the-counter and prescription medications and dietary supplements carefully. Pay particular attention to the correct dosage and to the potential side effects and interactions associated with the drug or supplement.
  • Make sure you understand the benefits as well as the potential risks of any medication you are taking. Look specifically for the warning labels of over-the-counter medications.
  • Keep a record of all the medications and supplements you take, and share it with all the doctors and pharmacists involved in your care.
  • Talk to your doctor before taking any new medication or supplement.
  • Use one pharmacy for all your prescription medications.
  • Ask your pharmacist whether you should take a particular medication with food or on an empty stomach and if there are any foods or beverages that could interact with the drug.
  • Report any side effects you experience from any medications to your doctor or pharmacist.
  • Take medications only as directed and do not take any medications that were prescribed for someone else.
  • Purchase supplements and vitamins from a reputable source.
  • Look for a United States Pharmacopeia (USP) notation on the bottle of your supplement. USP is an organization that sets standards for prescription and OTC medications, healthcare products, food ingredients, and supplements.


United States Pharmacopeia (USP)
US Food and Drug Administration


Canadian Medical Association
Health Canada


Drug interactions: what you should know. US Food and Drug Administration website. Available at: Updated September 25, 2013. Accessed April 22, 2015.
Avoiding drug interactions. US Food and Drug Administration website. Available at: Updated November 28, 2008. Accessed April 22, 2015.
Mallet L, Spinewine A, Huang A. The challenge of managing drug interactions in elderly people. [review]. Lancet. 2007;370:185-191.
Neuvonen PJ. Interactions with the absorption of tetracyclines. Drugs. 1976;11(1):45-54.
Sansone R, Sansone L. Tramadol. Psychiatry. 2009 April;6(4):17-21. Available at: Accessed April 22, 2015.
Schardt D. St. John's worts and all. Nutrition Action Health Letter website. Available at: Accessed April 22, 2015.

Revision Information

Health Library Search

Only show results from the selected categories.

2 Cholera condition

Cholera is an infectious disease that affects the intestinal tract....

3 Rickets condition

Rickets is disease that affects the bones. It causes them to soften and weaken....

Non-polio enteroviruses are a group of viruses that cause infections throughout the body. In most cases, enteroviruses do not lead to an illness or only cause a mild inf...

Biliary atresia is a blockage of bile ducts in infants. The bile ducts are tubes that let a fluid called bile pass from the liver to the gallbladder. Bile is made in the ...

Eosinophilic esophagitis is an inflammation in the esophagus due to an overreaction of the immune system. The esophagus is the tube that delivers food from your mouth to ...

Bacteremia is the presence of bacteria in the bloodstream. Most bacteremia will usually not lead to serious infection, most people will never be aware of it. However, ba...

11 Hypokalemia condition

Potassium is a mineral that is needed to help the heart, kidneys, and other organs function. Hypokalemia is lower than normal levels of potassium in your blood. All cell...

12 Hypocalcemia condition

Calcium is a mineral needed for bone health, muscle movement, and nerve function. Hypocalcemia means the level of calcium in the blood is lower than normal....

13 Hyperkalemia condition

Potassium is a mineral that is needed to help the heart, kidneys, and other organs function. Hyperkalemia is higher than normal levels of potassium in your blood. Potass...

14 Hypercalcemia condition

Calcium is a mineral needed for bone health, muscle movement, and nerve function. Hypercalcemia is higher than normal levels of calcium in your blood. Short-term or acut...

Wernicke encephalopathy is a brain disorder. It can be associated with a variety of symptoms such as confusion, lack of muscle coordination, and eye movement difficulties...

16 Taking Your Preemie Home lifestyle - women's health

Sulfites are compounds that are used to make foods and beverages last longer. Sulfite sensitivity is an abnormal reaction to these compounds. Foods that may contain sulf...

A baby who is small for gestational age (SGA) has a significantly lower weight than other babies of the same gestational age. Gestational age is the number of weeks into ...

Neurofibromatosis is a genetic disorder that causes tumors in the nervous system. Tumors develop in the nerves or the tissue that surrounds the nerves, called the myelin ...

Functional abdominal pain is pain that occurs with normal activity in the intestine. The pain recurs on a regular basis somewhere in the abdominal area. It is not caused ...