Signs of an Adverse Reaction to Medications

Pharmacist and patient discussing medication



Have you or your children ever experienced a “bad reaction” to a new medication? If so, you have suffered from what doctors and pharmacists call an “adverse drug reaction."


While all drugs are highly reviewed and regulated by Health Canada before ever hitting the shelves at your local pharmacy, adverse drug reactions to medications can still happen – even when you take your medications as prescribed. Usually, responses are mild, uncomfortable, and inconvenient but can also be life-threatening.   


Below, we cover more about adverse drug reactions, including what they are, the different types, and signs and symptoms to watch out for. Whether you suspect you are experiencing an adverse drug reaction or simply want to learn, our quick reference below can help prepare you to take care of yourself and your loved ones now or in the future.


If you suspect you or someone you know is currently experiencing a severe adverse reaction to a prescription medication or over-the-counter drug, we encourage you to seek immediate medical attention.


If your reaction is mild, book an appointment with your family doctor or speak to your local pharmacist as soon as possible. It is always critical to seek professional medical advice before changing your prescribed treatment plan or taking additional medications to address suspected reactions. 



What is an Adverse Drug Reaction?

An adverse drug reaction is an unintended, unwanted, and harmful response to a medication or drug that is accurately prescribed and correctly administered. In other words, the response to a medication or over-the-counter drug typically occurs due to no fault of you, your doctor, the drug manufacturer, or anyone else; something just didn’t sit well with your/your loved one’s system.


Because your body is always working to protect you and keep you in balance, adverse drug reactions result in negative, unpredictable outcomes that are not easily managed on your own. They will typically be quite evident and unpleasant, but that is by design. They signal that something is wrong and needs to be addressed immediately.


While you may not feel great at the time of an adverse drug reaction, you'll likely be happy later that your body did its job by sounding the alarms for you.



Are Adverse Drug Reactions the Same as Side Effects?

While many people use the terms “adverse drug reaction” and “side effect" interchangeably, they are not technically the same.


Pharmacist looking at medication bottle


Unlike adverse drug reactions, which are negative, unpredictable, and can require medical advice to resolve, side effects are generally anticipated and manageable. In some cases, side effects can even produce positive outcomes (such as weight loss or acne control).


If you experience manageable side effects, you will likely be advised to adjust your dose or to continue taking your medication as prescribed initially rather than discontinuing use. However, you should always discuss your unique situation with your local pharmacist or family doctor if you have any concerns with your treatment plan.



Types of Adverse Drug Reactions

Adverse reactions to medications can be allergic or non-allergic (idiosyncratic). Allergic reactions (or hypersensitivity) are caused by an immune system response. They occur most commonly with antibiotics, pain relievers, autoimmune disease drugs, and chemotherapy medications.


On the other hand, non-allergic reactions may present similarly to allergic reactions, despite not being triggered by the immune system. These reactions are most common with local anesthetics, opiates, aspirin, and radiocontrast media dyes used in imaging tests. Sometimes, there simply is no clear explanation for why an individual's non-allergic reaction occurred.


While many reactions are not due to incorrect dosing, this does not mean that human errors never occur. For example, you may be prescribed or administered too much medication for your unique personal health situation. Therefore, incorrectly taking or administering medication can cause dose-related adverse drug reactions.  


If you take multiple drugs to treat one or more health conditions, drug interactions can also cause adverse reactions – even if they do not cause reactions in other people. Your doctor and pharmacist are experts in avoiding negative drug interactions, but they can still happen unexpectedly.


Regardless of the reason or reaction, your doctor can advise you on what they believe caused the adverse outcomes. They may also opt to refer you to an allergist who can dive deeper into your unique sensitivities or allergies. Your local pharmacist can also complete a review of your medications to help investigate causes.



Common Allergic Drug Reaction Symptoms

Allergic drug reactions happen when the body's immune system kicks into overdrive after reacting to a medication. This drug hypersensitivity can happen even if you or a loved one only consumed a small amount. Reactions can occur when a drug is taken by mouth, injected, or applied topically. Usually, symptoms will occur within minutes of ingesting the drug.


Doctor on phone with patient


Allergic reactions typically result in symptoms related to the skin, nose, throat, lungs, ears, sinuses, and stomach. In addition, adverse drug reactions associated with hypersensitivity can come on quickly and range from mild to life-threatening.


Allergic drug reactions typically present as:


  • Fever
  • Swelling
  • Rashes
  • Hives
  • Itching
  • Watery eyes
  • Runny nose
  • Shortness of breath
  • Wheezing


Please evaluate the severity level if you experience any of the symptoms above. Next, call your doctor to make an appointment if symptoms are manageable and mild. Your local pharmacist may also be able to evaluate your situation. However, seek immediate medical attention if your symptoms are severe or life-threatening.



Less Common Allergic Drug Reaction Symptoms

Other types of allergic drug reactions can take days, weeks, or months to present and usually last longer than hypersensitivity-related adverse reactions. These types of responses are less common but are important to be aware of (as they can cause significant inflammation in the joints, kidneys, and skin). In addition, they can affect red blood cells and cause anemia.


Less common signs of drug allergy or drug-allergy-induced conditions include:


  • Joint pain, fever, nausea, swelling, and skin rash
  • Fatigue, shortness of breath, and irregular heartbeat
  • Swollen lymph nodes, general swelling, high white blood cell counts, and the resurgence of a hepatitis infection
  • Fever, confusion, swelling, and blood in the urine


If you or a loved one experience any symptom clusters above, do not delay booking an appointment with your doctor.



About Anaphylactic Adverse Drug Reactions

The most severe type of allergic drug reaction is called anaphylaxis. Anaphylactic adverse drug reaction severity varies, but immediate medical attention is recommended. This type of reaction is rare with drugs and medications but can be life-threatening.


Patient holding head and neck


Anaphylaxis can also occur due to food allergies and insect stings. Drug-related anaphylactic responses are most common in older adults, people with cardiovascular diseases, or individuals with asthma that is not adequately managed. Physical exertion, alcohol consumption, and infections can also increase the likelihood of severe anaphylaxis.


When anaphylaxis occurs, the reaction tends to impact multiple parts of the body simultaneously, including the skin, digestive tract, cardiovascular system, and airways.



Signs of Anaphylactic Drug Reactions


Symptoms of anaphylactic drug reactions include:


  • Trouble breathing due to tightening of the throat and airways
  • Dizziness or light-headedness
  • Seizure
  • Loss of consciousness
  • Drop in blood pressure
  • Vomiting
  • Diarrhea
  • Rapid, weak pulse
  • Nausea or cramps in the abdomen


As the situation can escalate within minutes, do not wait to call 911 or rush to the hospital if you suspect anaphylaxis is occurring.


Early signs include:


  • Headache
  • Confusion
  • Having a metallic taste in your mouth
  • Burning sensations on your palms or the soles of your feet
  • Tingling, itching, or burning sensation of the roof of your mouth 




In conclusion, while all drugs are highly reviewed in Canada before they ever make it to market, adverse drug reactions still occur across the country every day. These reactions range in severity and happen for different reasons - some of which are mysteries even to the most highly trained medical professionals.


Everyone is unique and responds to their prescribed medications and over-the-counter drugs in different ways. For this reason, it is always wise to take the initiative to learn about adverse drug reactions and what to do if you believe one is occurring. Your knowledge of adverse drug reactions could save a life or simply help relieve symptoms sooner for yourself or a loved one.


Adverse drug reactions are typically allergic but can also be non-allergic or dose-related. Adverse reactions are different from side effects because they are often negative, unwanted, unanticipated, and require medical attention (unlike side effects which are known and expected).


Reactions can occur immediately after consuming medication (either topically, by mouth, or via injection) or take days, weeks, or even several months to present symptoms.


Symptoms of adverse drug reactions vary but typically affect the skin, eyes, nose, throat, and lungs. If you have even mild reactions to prescribed medications or over-the-counter drugs, speak to a pharmacist near you and book an appointment with your family doctor. For severe reactions, seek immediate medical attention.



Seek Advice From Cook's Pharmacy

If you wish to speak to a trusted local pharmacist about your medications, Cook's Pharmacy is here to help! Reach out to any of our convenient locations in Kitchener, Waterloo, Cambridge, Wellesley, or New Hamburg today!



Any medical or pharmaceutical information on this site is provided as an information resource only and is not to be used or relied on for any diagnostic or treatment purposes. This information does not create any patient-pharmacist relationship, and should not be used as a substitute for professional diagnosis and treatment.


Please consult your healthcare provider before making any healthcare decisions or for guidance about a specific medical condition.


Cook’s Pharmacy and its subsidiaries expressly disclaim responsibility and shall have no liability, for any damages, loss, injury, or liability whatsoever suffered as a result of your reliance on the information contained in this site.




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