Drug Interactions

Drug interactions usually occur when taking more than one drug at the same time, and the risk changes based on age, underlying diseases and lifestyle. Some drug interactions can be deadly.

When a person takes a drug, it’s critical that he or she first consider the potential for interactions with other substances in the body. Drugs can react to other medications, health supplements and even food or alcohol. There are a few instances when such reactions are the goal because they increase the effectiveness of the drugs, but more often, mixing medicines can lead to unwanted and dangerous side effects.

How Drug Interactions Occur

Drug interactions can occur in numerous ways — from combining drugs outside the body to the manner in which the body processes the drug. Such interactions also can vary from person to person because of changes in the absorption, distribution, metabolism and excretion of the drug within the body. Because of this, drug reactions largely are unpredictable, even with known interactions.

Particularly dangerous reactions can occur when a person takes two or more drugs that have similar properties because the effects are magnified. Also dangerous is a situation in which the person ingests drugs with opposite properties that cancel the medicinal benefit of both drugs. Another common adverse interaction can occur when one drug alters the concentration of a substance that is normally present in the body.

Factors that Affect Drug Interactions

There are some common factors that increase the risk of drug interactions. These include a genetics, age, diet, exercise, underlying diseases, current medications and the period of time that elapses between the administration of the two drugs.

But even allowing for these factors does not guarantee that a drug will be risk-free. Some interactions can take weeks to develop, and some can dissipate after a few weeks, with seemingly no explanation. And when medication is not taken on a regular basis, or if it’s only taken as needed, drug interactions are much more difficult to predict.

Who is At Risk

Older patients typically take more medicines than their younger counterparts, which increases the potential for adverse interactions. The Wall Street Journal reported that more than 2 million Americans between the ages of 57 and 85 are at risk of major drug-drug interactions, according to a 2008 study published in the Journal of the American Medical Association.

In addition, patients are most vulnerable when they are introducing a new drug or when they are withdrawing from a medication.

Types of Drug Interactions

About 40 percent of U.S. residents have prescriptions for four or more medicines, according to a 2008 consumer update from the U.S. Food and Drug Administration (FDA). That means that a large number of patients have the potential for drug interactions and reactions, which can occur when medications are taken with other drugs, dietary supplements, food and/or alcohol.

Drug Interactions with Other Drugs

Interactions between drugs can include not just prescription medicines, but also over-the-counter (OTC) medicines. Many OTC drugs were once prescriptions and are not as benign as some consumers are led to believe. When taking combinations of medicines, it is vital that patients read labels on OTC drugs and ask pharmacists and doctors to check for dangerous drug interactions with their prescription medicines. One frequent adverse reaction happens when a person unknowingly overdoses on a common ingredient, such as acetaminophen (Tylenol).

The Washington Post reports that unintentional drug poisonings caused 20,000 deaths in 2004, according to a report by the Centers for Disease Control and Prevention (CDC).

Drug Interactions with Supplements

Consumers often make the assumption that because they are readily available, supplements must be safe. In and of themselves, that may be true, but when combined with drugs, supplements can cause serious adverse reactions.

The FDA cites research that shows at least half of American adults regularly use dietary supplements, which are defined as “products taken by mouth that contain a dietary ingredient.” According to the agency, these include vitamins, minerals, amino acids, and herbs or botanicals.

St. John’s wort, vitamin E, ginseng and Ginko biloba all have been touted for their ability to boost certain health aspects. Unfortunately, they also interact with various widely prescribed drugs and cause life-threatening reactions.

Because supplements are not strictly regulated, the levels of active ingredients in each dose can vary. In addition to the uncertainty of how the supplement will affect a patient each time it’s taken, the danger is compounded by unknown interactions with other medications. Furthermore, patients are risking their health by taking dietary and herbal supplements that have no proven effectiveness.

Drug Interactions with Food

Food affects the rate and degree at which a medicine is absorbed by the body. The most common interaction between a drug and food causes a slowed absorption, making the medicine less effective. However, some medicines are intended to be taken with food because doing so prevents stomach irritation.

The opposite is true, too: Drugs can directly interfere with the absorption of nutrients, such as vitamins and minerals, from foods. Drugs also can indirectly affect a person’s nutrition by increasing or decreasing his or her appetite.

In addition, patients need to be aware that alcohol can trigger adverse responses in the body when taken with drugs. Taken with a sedating medication, alcohol can intensify the drowsiness. This can be especially dangerous if the patient has to drive or operate heavy machinery.

Drugs with Known Interactions

With so many prescription and over-the-counter medicines available to consumers, it is vital that they check, and even double-check, for interactions. In the United States, three of the most commonly used prescription drug classes — antidepressants (SSRIs), blood pressure medication (HCTZ) and cholesterol drugs (statins) — can have a host of interactions if patients are not informed and then misuse them.

Antidepressants (SSRIs)

The most widely prescribed class of antidepressants today are selective serotonin reuptake inhibitors (SSRIs). They work to elevate the serotonin levels in the brain, which is thought to ease the symptoms of depression.

Some popular SSRIs are:

  • Prozac
  • Zoloft
  • Paxil
  • Lexapro
  • Unfortunately, SSRIs can have a host of unpleasant side effects and life-threatening complications, such as suicidal thoughts and behaviors in young adults and birth defects for babies whose mothers took the drugs during pregnancy. One serious complication, serotonin syndrome, can occur when an SSRI interacts with other drugs, especially pain medications, that contain the same ingredients. The onset of serotonin syndrome can occur within minutes and can be deadly if not treated immediately.

    St. John’s wort, a dietary supplement used to treat depression, can cause serotonin syndrome when it is combined with an SSRI. SSRIs also are known to interact with OTC antihistamines, causing extreme drowsiness.

    There are no proven interactions with food when a patient takes an SSRI. At least one study, however, suggests that eating kiwifruit, which has high natural levels of serotonin, can boost the effectiveness of SSRIs. Also, certain SSRIs can cause an upset stomach or heartburn if they are taken on an empty stomach.

    Blood Pressure Medication

    Some of the most common medications used to treat high blood pressure, or hypertension, are diuretics known as hydrochlorothiazides (HCTZ). Blood pressure is a measure of the force that blood exerts on vessels as it moves through the body. If it is high, the body must worker harder to pump the blood, which strains the heart and ultimately can lead to a heart attack or stroke. HCTZ drugs essentially pull the extra water from the body, decreasing the volume of blood so the body doesn’t have to work as hard.

    HCTZ drugs should not be taken with heart-rhythm medication because the combination can lower potassium levels to the point that fatal cardiac arrhythmia can occur. OTC decongestants also should not be used when a patient is taking HCTZ drugs because they decrease the effectiveness of the blood-pressure medication.

    One food interaction has been documented for HCTZ drugs. Glycyrrhizin — found in black licorice, some sweeteners and herbal teas — can have a negative effect on potassium levels, which can damage the heart.

    Cholesterol Drugs (Statins)

    Approximately 24 million people in the United States take a prescription from a class of medicines called statins to lower their cholesterol. The body needs cholesterol to function, but high levels of the substance can lead to plaque buildup in arteries, which can eventually block blood flow and lead to heart attacks and stroke. Statins work by halting the action of a chemical in the liver that is needed to make cholesterol.

    One of the most common side effects of statins is muscle soreness. Mixing statins with certain drugs, dietary supplements or foods can damage muscles and even lead to kidney failure. For this reason, patients are advised not to mix statins with prescription oral fungal (yeast infection) medication, vitamin B complex or grapefruit juice.

    How to Prevent Drug Interactions

    Preventing drug interactions is a task that all patients should take seriously. To each doctor’s visit, patients should take a list of medications they are taking, including dietary supplements. This is the first step in avoiding a dangerous drug interaction because a doctor will be able to create a more educated treatment plan if he or she knows which medicines are being taken.

    When receiving new prescriptions, patients should ask their doctor if they will interact with their current medications. The doctor should have checked this before issuing the prescription, but patients should not assume that has happened. In an increasingly busy healthcare setting, things slip through the cracks, and it is the patient’s responsibility to safeguard his or her health.

    When dropping off a new prescription at the pharmacy, patients should ask about drug interactions. It’s also a good idea for patients to use the same pharmacy for all of their prescriptions so that interactions will be spotted more easily in the computer system.

    Patients also can take charge of their health by using an online tool to check interactions each time they are prescribed a new drug, they buy an OTC medicine or they pick up a dietary supplement.

    Hide Sources

    1. Payne, J. (2007, February 27). A Dangerous Mix. The Washington Post. Retrieved from http://www.washingtonpost.com/wp-dyn/content/article/2007/02/23/AR2007022301780.html
    2. Goldstein, J. (2008, December 24). Millions of Older Americans at Risk from Drug Interactions. The Wall Street Journal. Retrieved from http://blogs.wsj.com/health/2008/12/24/millions-of-older-americans-at-risk-from-drug-interactions/
    3. Qato, D. et al. (2008, December 24). Use of Prescription and Over-the-counter Medications and Dietary Supplements Among Older Adults in the United States. The Journal of the American Medical Association. Retrieved from http://jama.jamanetwork.com/article.aspx?articleid=183125
    4. U.S. Food and Drug Administration. (2012, July 19). Drug Interactions: What You Should Know. Retrieved from http://www.fda.gov/drugs/resourcesforyou/ucm163354.htm
    5. U.S. Food and Drug Administration. (2008, November 28). Avoiding Drug Interactions. Retrieved from http://www.fda.gov/forconsumers/consumerupdates/ucm096386.htm
    6. Bobroff, L., Lentz, A. and Turner, R. (May 2009). FOOD/DRUG and DRUG/NUTRIENT INTERACTIONS: What You Should Know About Your Medications. University of Florida.