What is a drug interaction, and how does it differ from a side effect?

A drug interaction is a change in how a drug works in the body when taken with certain other drugs, foods, or dietary supplements, or when a person has specific medical conditions [1]. This interaction can make a drug less effective, more effective, cause unexpected side effects, or alter how one or both drugs work [1].

For example, aspirin may interact with blood thinners, statins with grapefruit, or ginkgo with blood thinners [1]. Some drugs can also interact with pre-existing health conditions; for instance, if you suffer from a peptic ulcer, taking aspirin may cause a problem [1].

The Difference Between Drug Interaction and Side Effects

While a drug interaction is considered a change in how a drug works due to external or internal factors, side effects are unwanted—and usually bothersome—effects caused by the drug itself [1]. Most side effects are mild, such as stomach aches, dry mouth, or drowsiness, and usually disappear after stopping the medication [1]. However, some side effects can be more serious [1].

Sometimes, a drug can interact with a disease you have and cause a side effect. For example, if you have a heart condition, some decongestants can cause a rapid heartbeat [1].

Common Types of Drug Interactions

• Drug-Drug Interactions: These occur when two or more drugs interact with each other. For example, mixing a sleep aid (sedative) with an allergy medication (antihistamine) can slow your reaction time and make driving dangerous [2].
• Drug-Food/Beverage Interactions: These result from drugs interacting with foods or drinks. For example, mixing alcohol with certain medications may lead to feeling tired or slowing down reaction times [2].
• Drug-Condition Interactions: These may occur when a pre-existing medical condition makes certain drugs harmful. For example, if you have high blood pressure, you may experience an unwanted reaction if you take a nasal decongestant [2].

How to Avoid Drug Interactions?

To reduce the risks of harmful drug interactions and side effects, it is essential to take preventative steps:

1. Read Labels Carefully: Read the label of every drug, whether prescription or over-the-counter, every time you use it [2]. Over-the-counter medication labels contain important information about ingredients, uses, warnings, and instructions [2].
2. Talk to Your Doctor or Pharmacist: When starting any new medication, discuss all the drugs you are taking (including over-the-counter medications, dietary supplements, vitamins, herbs, and minerals), as well as the foods you eat [2]. Ask your doctor or pharmacist the following questions:
   • Can I take this medication with other drugs? [2]
   • Should I avoid specific foods, drinks, or other products? [2]
   • What are the signs of a potential drug interaction that I should be aware of? [2]
   • How will the drug work in my body? [2]
3. Be Aware of Active Ingredients: Different over-the-counter medications may contain the same active ingredient. If you are taking more than one over-the-counter medication, pay attention to the active ingredients used in the products to avoid consuming too much of a specific ingredient [2].
4. Special Circumstances: Under certain conditions, such as pregnancy or breastfeeding, you must speak with your doctor before taking any medication [2].

When to Seek Medical Help?

If you suspect you are experiencing a drug interaction or a serious side effect, contact your healthcare provider immediately. In life-threatening emergencies, such as a severe allergic reaction (anaphylaxis) that may include difficulty breathing or severe swelling, seek emergency care right away [1]. You can visit Drug interactions: How to avoid complications and use your medication safely? (Arabic) for more information.

Medical references

• Drug Reactions
• Drug Interactions: What You Should Know