Side effects or allergic reaction?

Despite the fact that users are strongly encouraged to be able to differentiate between these two scenarios, a significant number of people continue to be confused. What is the true meaning of side effects and allergic reaction, and what is the distinction between the two?

15 Jan 2024 04:39pm
Sinar Daily AI generated image
Sinar Daily AI generated image

All medications, including Controlled Medicines, over-the-counter (OTC) medications, health supplements, and traditional products have the possibility to cause side effects or allergic reactions. According to statistics, side effects accounted for the most undesirable consequences of medications intake. In contrast, only five to ten percent of incidents are associated with symptoms related to medication allergies.

Despite the fact that users are strongly encouraged to be able to differentiate between these two scenarios, a significant number of people continue to be confused. What is the true meaning of side effects and allergic reaction, and what is the distinction between the two?

Side effects

Definition of side effects

Side effects are known, unwanted effects that are caused by a medication at its normal dose and could either be beneficial, harmful, or neutral. These effects are a consequence of the way the medicine functions in the body and are not related to the body's immune response. Side effects are typically indicated on the label and in the patient information leaflet.

Categories of side effects

In general, side effects fall into six categories, which are as follows:

a. Known side effects

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Most medications have side effects that are well known. For instance, certain first-generation antihistamine medications like promethazine, dexchlorpheniramine, and chlorpheniramine can cause drowsiness. On the other hand, aspirin has been linked to gastritis.

b. Side effects due to overdose

This side effect arises when a person takes medications in excess of the recommended dosage. Overdosing can have very serious and even deadly repercussions. An excessive intake of paracetamol (more than the recommended 4 grams per day) might produce liver failures, which is one example of a side effect associated with an overdose.

c. Side effects that occur indirectly

An example of an indirect side effect is when a patient takes antibiotics to treat an infection and develops diarrhoea. This is a result of the antibiotic's effect on the beneficial bacteria in the stomach.

d. Side effects due to drug interactions

Taking medicine with food or other medications can cause interactions. For example, when taken concurrently, warfarin and non-steroidal anti-inflammatory drug (NSAIDS) painkillers, including ibuprofen, diclofenac, mefenamic acid, and others, might increase the risk of gastrointestinal bleeding. Vitamin K-rich vegetables like spinach, broccoli, and kale might have an interaction with warfarin that may reduce the effects of warfarin.

e. Side effects that cause a disease or symptoms to worsen

An example of this type of side effect would be someone with asthma who is taking propranolol to treat their palpitations (tachycardia). Taking propranolol can cause the asthma to worsen and the patient to experience shortness of breath.

f. Side effects of an idiosyncratic nature

Certain medications may result in highly incomprehensible (idiosyncratic) side effects. For instance, levofloxacin and other quinolone-type antibiotics may have negative effects on tendons, although the exact mechanism underlying this response is still uncertain.

Reporting side effects

It is advisable to speak with a doctor or pharmacist when experiencing any side effects. The doctor might usually adjust the dosage regimen or discontinue the medicine that has been identified as the cause of the side effects based on the symptoms presented.

Additionally, patients are encouraged to report the side effects experienced through the National Pharmaceutical Regulatory Agency (NPRA) website. Reports collected indirectly can contribute to the improved safety of medications in Malaysia.

Allergic reaction

Definition of drug allergy

In short, an allergy reaction is a hypersensitivity reaction to the medicine. Allergic reactions occur when the body’s immune system begins to recognise the medication as a “foreign body" and hence produces antibodies that will react with the medication, causing allergic symptoms.

Symptoms and treatment of drug allergies

Allergic symptoms can range from mild to severe, with skin reactions being the most frequently involved. Commonly seen mild reactions include skin itchiness, rashes, and swelling. Loss of consciousness, shortness of breath, and anaphylaxis are symptoms of serious medication allergies.

The most serious form of allergic reaction is anaphylaxis, which is a life-threatening reaction involving several organs whose signs include tongue or throat swelling, fainting, difficulty breathing, very low blood pressure, and weak pulses. Anaphylaxis reactions usually occur rapidly, within seconds or minutes of exposure to the suspected medicines.

Depending on the severity of the symptoms, various measures can be taken to deal with the allergy symptoms. The first thing to do is to stop taking any medications that might be causing allergies. At the same time, the patient should be seeking any further examination by the doctor.

An examination by a doctor can determine whether the patient is truly allergic to a medicine. Plus, the doctor can ascertain whether the patient requires treatments to relieve the symptoms of the allergy. When an allergic reaction happens, antihistamine medications like diphenhydramine and chlorpheniramine are used to alleviate symptoms and slow down the reactive substances in the immune system.

Besides, corticosteroid medications can be used orally or by injection to alleviate inflammation. Examples of these medications are dexamethasone and prednisolone. Anaphylaxis and other severe allergy symptoms call for more intensive in-patient care that includes breathing support, blood pressure monitoring, and epinephrine injections.

Drug Allergy Card

A drug allergy card will be given to the patients identified by the doctor as having a medication allergy. The allergy card contains a serial number, the patient’s name, an identification number, the name of the medications that cause allergies, and brief descriptions of the allergic reactions experienced. This card is important so that healthcare professionals can be aware of the patient’s existing allergy, thereby preventing the patient from taking medications that can cause allergies.

Details of patients with drug allergies shall be noted in the Rekod Maklumat Pesakit yang Mengalami Alahan Ubat at each Ministry of Health Malaysia health facility. After that, this data will be forwarded to the Pharmaceutical Services Programme, which will create a database of individuals with medication allergies.

Patients should bring along this card at all times and show the card to doctor, dentist, pharmacist, nurse or other healthcare providers when receiving treatment or medication. Currently, there are several private facilities that have also established a recording system to monitor patients with allergies.


It is recommended that patients or the general public become familiar with steps to identify side effects and allergies by getting advice from a healthcare professional. Knowing about these two conditions can also help patients address side effects and medication allergies effectively.

If there are any inquiries regarding medicines, please call the National Pharmacy Call Centre (NPCC) at the toll-free number 1-800-88-6722 during weekdays from 8am to 5pm, except on public holidays.

Prepared by Benice Goh Sin Yee, pharmacist at Hospital Miri, Sarawak.