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Common Adverse Drug Reactions: What to Watch Out For

Medically reviewed by Elfred Landas, MD · General Practitioner · Maxicare Primary Care Center

Written by Lorraine Bunag, R.N. · Updated Jul 07, 2021

Common Adverse Drug Reactions: What to Watch Out For

Medications are supposed to cure us of whatever is compromising our health. But if we develop common adverse drug reactions, they will cause us more trouble, especially if it is due to an allergy. What medications trigger allergies? What are the possible drug allergy treatments?

Drug Allergy vs Adverse Drug Reactions

Adverse drug reactions

When we say common adverse drug reactions, we are talking about “noxious and unintended responses” to the medication even though they are given under normal conditions of use. When a person develops adverse reactions to a drug, the doctor may discontinue the use of the medication, or at the very least reduce its dose.

Drug allergy

A drug allergy, on the other hand, causes adverse drug reactions, but they happen because our immune system abnormally reacts to the medication or its components. It is worth noting that you can be allergic to any drug depending on your immune system’s makeup. However, some drugs are more likely to cause an allergic reaction than others.

To sum it up, a person may experience common adverse drug reactions, but it does not automatically mean that they are allergic to the drug. After all, true allergic reactions to medication are fairly rare, accounting for only 5% to 10% of all the adverse drug reactions.

Why Do Drug Allergies Happen?

A drug allergy happens because the immune system considers the drug – or a component of that drug – as “foreign” or “dangerous.” When that happens, we can call the drug as an allergen – or a substance that causes allergic reactions.

Since the immune system feels that the allergen is attacking the body, it will create substances called “antibodies.” The role of these antibodies is to defend the body from the presumed danger by commanding the white blood cells to create histamines. This histamine will create allergic symptoms.

Common Drugs That Cause Allergic Reactions

Now that we have cleared up the difference between adverse drug reactions and allergic reactions, it is time list down the common drugs that cause allergies.


Antibiotics are medications used to treat bacterial infections – either to kill the bacteria or to reduce its growth. Typically, the doctor prescribes it after a laboratory test or a physical examination confirms the presence of infection.

If you have ever been confined in a hospital and the doctor prescribes you intravenous antibiotics, you probably know the drill. They will have to test first whether you are allergic to the antibiotic.

They do this by performing “intradermal skin testing” wherein they introduce a small amount of the medication under the surface of the skin. Afterward, you wait for about 20 to 30 minutes to see if the area where they injected the drug becomes swollen or irritated. If a reaction takes place, you may be allergic to the drug.

This skin testing is essential because antibiotics not only cause common adverse drug reactions, they also trigger an allergy.

Allergy Skin Tests: How Do Doctors Check for Allergies?


A specific drug that a lot of people claim to be allergic to is penicillin. However, we should clarify that not all people who report being allergic to this drug experience true allergic reactions.

If you experience common adverse drug reactions to penicillin, you are likely to develop symptoms like headache, nausea, diarrhea, and vaginal itching.

Sulfa Drugs

Sulfa drugs are also antibiotics. However, they contain substances called sulfonamides. The interesting thing about sulfa drugs is that the person may not be necessarily allergic to the sulfonamides group or sulfur in general. They are just allergic to the sulfa antibiotic drugs.

For instance, there are medications for diabetes and arthritis that contain sulfonamides and people do not necessarily need to avoid them just because they are allergic to sulfa antibiotics.

Still, Sulfa drugs cause common adverse drug reactions like nausea and vomiting, headache, dizziness, diarrhea, and lethargy.


NSAIDs or non-steroidal anti-inflammatory drugs are primarily used to reduce pain or fever. Common examples of NSAIDs are ibuprofen, mefenamic acid, aspirin, and naproxen. They are quite notorious for some common adverse drug reactions ranging from headaches and dizziness to stomach pain and ulcers.

As you will notice, many NSAIDs are over-the-counter medications, allowing people to have access to them even without a physician’s prescription. Despite being safe for most people, itis still possible for others to develop some allergic reactions to NSAIDs.


Insulin is a common drug given to diabetic patients as it helps control their blood sugar levels. However, it can cause allergic reactions, especially if it is animal-derived. If you are allergic to insulin, you may experience localized or systemic symptoms. When we say localized, it only affects certain parts of the body. When it is systemic, it affects the entire body.

Once again, you can develop adverse reactions even if your immune system is not involved. In those times, you are not experiencing allergic reactions.

Signs and Symptoms of Drug Allergy

If you have an allergy to certain medications, you may experience the symptoms within an hour after taking the drug. At times, you may experience them after a few hours, days, or even weeks later.

The most common symptoms of drug allergy are:

  • Itchy, watery eyes
  • Hives
  • Skin rashes
  • Itching
  • Runny nose
  • Wheezing
  • Fever
  • Shortness of breath
  • Swelling
  • Anaphylaxis

Signs and Symptoms of Anaphylaxis

Anaphylaxis is a life-threatening allergic reaction. Commonly, anaphylaxis reactions develop within minutes after taking the medication. Symptoms include:

  • Tightening of the air passages causing difficulty breathing
  • Lightheadedness or dizziness
  • Nausea or abdominal pain
  • Vomiting or diarrhea
  • A drop in blood pressure
  • Loss of consciousness
  • Seizure
  • Weak, rapid pulse

Allergy Symptoms You May Experience Days or Weeks After

  • Nephritis or inflammation of the kidneys
  • Drug-induced anemia
  • Serum sickness which may show as joint pain, swelling, fever, nausea, and rashes
  • DRESS or drug rash with eosinophilia and systemic symptoms. This shows up as rashes with high white blood cell count; it is also accompanied by swollen lymph nodes.

What to Do When You Experience Drug Allergy

If you suspect an allergic reaction and you experience mild symptoms, consult your doctor as soon as possible.

Should you develop severe reactions, especially related to anaphylaxis, go to the emergency room.

Drug Allergy Treatments

The goal of drug allergy treatments is to reduce the symptoms and, if possible, prevent severe reactions. Treatments could be:

  • Antihistamines for mild symptoms like hives, rashes, and itching.
  • Bronchodilators to relieve asthma-like symptoms such as wheezing and coughs.
  • Corticosteroids, which can be applied on the skin, given intravenously, or taken orally.
  • Epinephrine to treat anaphylaxis.

Key Takeaways

Once again, common adverse drug reactions are different from allergic reactions. Allergies are caused by our immune response. Since allergic reactions are dependent on a person’s immune system, we will have no way of knowing how a person will react to a drug allergen. Although we have drug allergy treatments, avoiding drug allergen is still the best course of action.

Learn more about Other Allergies here.


Hello Health Group does not provide medical advice, diagnosis or treatment.

Medically reviewed by

Elfred Landas, MD

General Practitioner · Maxicare Primary Care Center

Written by Lorraine Bunag, R.N. · Updated Jul 07, 2021

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