What’s the difference between a side effect and a drug allergy?

When you go to the pharmacy counter to fill out a new prescription, you may notice that the pharmacist or pharmaceutical technician always asks if you have any known drug allergy.

It is essential to record allergies to avoid giving drugs that may cause allergic reactions. Allergic reactions can range from rash or hives to allergic reactions.

But did you know that many patients report that their medications are “allergic,” in fact only as side effects? It can lead to unnecessary drug retention. Read on to learn more about the difference between adverse drug reactions, drug allergies, and side effects.

How to Tell Drug Allergy from Side Effects

Doctors call these unnecessary or unexpected symptoms “adverse reactions,” and they are not uncommon.

However, the American Academy of Allergy, Asthma, and Immunology says that true allergies account for only a small number of these reactions, about 5% to 10%. On the contrary, many reactions are side effects, troublesome, but not severe.

They are often mild, like stomach pain or drowsiness, and go after you stop taking medicine. The actual drug allergies you should know are different, with reactions ranging from mild to life-threatening.


Adverse drug reaction (ADR) can be defined as an adverse drug reaction during routine clinical use. ADRs can be divided into two subtypes: type A and type B. ‘

Type A ADRs are dose-dependent and predictable; they increase the known pharmacological effects of the drug and can be mild, moderate, or severe. Examples of Type A adverse reactions include drug overdose, drug side effects, and drug interactions.

Type B adverse reactions are rare, unpredictable, and have nothing to do with drug dosage. Examples of Type B adverse reactions include drug intolerance and drug characteristics.

The drug classes that most commonly cause ADR in adults are adrenal corticosteroids, antibiotics, anticoagulants, anti-tumor and immunosuppressive drugs, cardiovascular drugs, non-steroidal anti-inflammatory drugs (NSAIDs), and opioids.


Side effects can be defined as “undesirable side effects that occur regardless of the dosage.” Before the drug enters the market, the side effects of the drug will be extensively studied and monitored during clinical trials. Since side effects are primarily predictable, doctors or pharmacists will warn patients about possible effects during treatment.

Unlike drug allergies, after taking the drug for a few weeks, the side effects usually subside on their own over time. Many patients believe that they are allergic to a particular medicine because they feel nauseous while taking the drug.

As mentioned above, drug allergy caus by an overreaction of the immune system. The feeling of nausea has nothing to do with the immune system. Certain drugs can cause nausea for many reasons.

For example, non-steroidal anti-inflammatory drugs can irritate the stomach wall and cause sickness. In this case, eating something before taking medicine can usually relieve nausea. Although the definition of side effects includes “undesired effects,” I want to point out that not all drug side effects are undesirable.

 Certain types of drugs are even use because of their side effects. An example of this is the drug mirtazapine (Remeron) used in patients with anorexia because of its potential to increase appetite and cause weight gain.

Should I Get Medical Help?

If you have difficulty breathing or have a severe allergic reaction, go to the emergency room or call 911.

These are life-threatening situations. Most drug allergies respond to treatment, but you must take them seriously and act quickly.

 If your body does not feel normal or correct in response to prescription drugs. Call your doctor to see your symptoms and when they start. The side effects may be temporary until your child uses this medicine. Or they may indicate that you need a different form of treatment.

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