What Are the 3 Main Drug Interactions?

Medically Reviewed on 10/5/2022
3 Main Drug Interactions
A drug interaction occurs when a meal, supplement, or drug alters how your body processes the medication.

Most of the time, medications improve our quality of life. They reduce aches and pains, fight infections, and manage many other conditions such as high blood pressure and diabetes

However, they can also cause adverse effects such as drug interactions, side effects, and allergies.

What is a drug interaction?

If you use multiple medications and see various medical professionals, you may be more vulnerable to drug interactions, which occur when a meal, supplement, or drug alters how your body processes medications. Such interactions may increase the potency of a drug—making a typical dose into an overdose—or decrease its potency or make it completely ineffective. 

According to researchers at Harvard Medical School, individuals must understand their medications and become aware of their responses to them. Their research focuses more on investigating how people might effectively control their drugs to prevent negative effects.

3 types of drug interactions

  1. Drug–drug interactions:
    • Drug-drug interactions are described as a pharmacologic or clinical reaction to the administration of a drug combination that differs from the expected effects of the two drugs when given alone. Drug interactions can have negative effects on people, reduce the effectiveness of treatments, or even cause injury. Although there are more than 100,000 different possible medication interactions, the majority never really have a negative effect. Drug interactions occur occasionally but not frequently. Using data from prescription drug claims, a survey of two sizable health plans estimated the probability of probable drug interactions to be between 6.2 and 6.7 percent per year.
    • A drug interaction occurs when one drug affects the cytochrome enzyme that processes another. For instance, the antibacterial Flagyl (metronidazole) inhibits the enzyme CYP2C that breaks down the blood thinner Coumadin (warfarin). When the two drugs are used simultaneously, the blood thinner may remain in the body longer, increasing the risk of life-threatening bleeding.
    • Dilantin (phenytoin), an antiseizure medication, increases the excessive production of CYP3A4, an enzyme that metabolizes estradiol (a substance used in low-dose contraceptives).
    • In other cases, two medications taken for unrelated purposes may have the same outcome, simulating an overdose. This can occur when over-the-counter painkillers such as aspirin, Motrin (ibuprofen), Aleve (naproxen), and, to a lesser extent, Tylenol (acetaminophen) are combined with blood thinners such as warfarin and clopidogrel. The combination can cause significant bleeding because the painkillers have anti-clotting properties.
  2. Drug–food interactions:
    • Drug–food interactions (or drug-nutrient interactions) occur when a food alters a drug's anticipated effect. For instance, grapefruit juice enhances the effects of several antihypertensive medications, whereas milk reduces the absorption of antibiotics such as tetracycline or ciprofloxacin.
    • Grapefruit juice inhibits the enzyme that breaks down statins, and those who take a lot of Lipitor (atorvastatin) or Zocor (simvastatin) may have muscle discomfort and other adverse effects from a statin "overdose."
    • Warfarin and fish oil supplements together may have a similar effect, increasing the danger of life-threatening hemorrhage. Iron supplements can reduce the effects of Synthroid (levothyroxine), a drug used to treat an underactive thyroid.
  3. Drug–condition interactions:
    • When a medication affects an underlying illness or condition, this is referred to as a drug–disease (or drug–condition) interaction. Drug interactions with diseases can increase the risk of unfavorable outcomes. For instance, aspirin makes people with peptic ulcers more prone to bleeding; oral decongestants, which are commonly present in over-the-counter remedies for colds, allergies, and coughs, can increase heart rates in people with high blood pressure.


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How can a person avoid drug interactions?

You can take the following actions to prevent drug interactions:

  • Inform your healthcare practitioner of all prescription and over-the-counter medications you are currently taking or plan to take. Moreover, let your doctor know if you use any herbal remedies, dietary supplements, or vitamins.
  • Inform your healthcare practitioner of any additional illnesses you may have, such as diabetes or high blood pressure.
  • Ask your doctor or pharmacist the following queries before taking a medication:
    • What is the purpose of the drug?
    • How should I administer the medication?
    • Should I avoid any certain meals or beverages, as well as other medications, while taking this medication?
    • Can I safely use this medication along with the other medications I currently take?
    • Do I need to be aware of any potential drug interactions?
    • What symptoms indicate a medication interaction?
    • What should I do if a drug interaction occurs?
  • Follow the advice of your doctor when using medications. Always read the written instructions and information provided with a drug. Important details concerning potential drug interactions are included on the labels and packaging inserts of medications.

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Medically Reviewed on 10/5/2022
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