What are the symptoms of an adverse drug reaction?

Studies estimate that serious adverse drug reactions (ADRs) affect 6.7% of hospitalized patients and are the fourth leading cause of death in the United States [1.2.1]. Knowing what are the symptoms of an adverse drug reaction is crucial for medication safety.

Quick Summary

Recognizing an adverse drug reaction involves identifying symptoms that range from mild, like skin rashes or nausea, to severe, such as anaphylaxis. This overview details common and severe symptoms and what to do if you suspect a reaction.

Key Points

• ADR vs. Side Effect: An adverse drug reaction (ADR) is a harmful and unintended response, while a side effect is a known, often predictable effect of a drug [1.10.2].

• Common Symptoms: The most frequent ADR symptoms include skin rashes, hives, itching, nausea, diarrhea, and dizziness [1.3.1, 1.3.4].

• Severe Reactions are Emergencies: Anaphylaxis (difficulty breathing, swelling, low blood pressure) and Stevens-Johnson syndrome (flu-like symptoms followed by a blistering rash) require immediate medical attention [1.6.2, 1.7.1].

• Know the Risk Factors: Risk for ADRs is higher in older adults, those taking multiple medications (polypharmacy), and individuals with kidney or liver disease [1.11.1].

• Timing Varies: Reactions can happen within minutes of taking a drug, or they can be delayed, appearing hours, days, or even weeks later [1.4.1].

• Report Suspected Reactions: If you suspect an ADR, contact your doctor. Report the event to programs like the FDA's MedWatch to improve medication safety for all [1.9.3].

• Organ Damage is Possible: Some ADRs can cause serious damage to organs like the liver or kidneys, with symptoms such as jaundice, dark urine, or decreased urination [1.8.2, 1.4.1].

An adverse drug reaction (ADR) is a harmful and unintended response to a medication taken at a normal dose [1.10.2]. While the term is often used interchangeably with 'side effect,' ADRs are distinct in that they are always harmful, whereas side effects can sometimes be neutral or even beneficial [1.10.2, 1.10.3]. Recognizing the signs of an ADR is critical for preventing serious health consequences. These reactions can occur within minutes or after days or weeks of exposure [1.3.1, 1.4.1].

Distinguishing Adverse Drug Reactions from Side Effects

A key difference lies in predictability and severity. Side effects are often anticipated effects of a drug that are not part of the main therapeutic goal [1.10.3]. For example, drowsiness from an antihistamine is a known side effect. An ADR, however, is a noxious response that is not intended [1.10.2]. ADRs are broadly classified into two main types:

• Type A (Augmented): These reactions are predictable from the drug's known pharmacology and are often dose-dependent. They are common and an example is bleeding caused by anticoagulant medications [1.5.2, 1.10.3].
• Type B (Bizarre): These are unpredictable reactions that are not related to the drug's pharmacological effect and are not dose-dependent. They include things like drug allergies and idiosyncratic reactions, which may be influenced by patient-specific factors like genetics [1.10.3, 1.5.1].

Common Symptoms of an Adverse Drug Reaction

ADRs can affect nearly any part of the body, but some symptoms appear more frequently than others. Over 90% of ADRs do not involve an allergic immune system response [1.4.4].

Common Manifestations

The most frequently reported ADRs include a range of general and system-specific symptoms [1.3.4]:

• Gastrointestinal issues: Nausea, vomiting, and diarrhea are among the most common symptoms [1.3.4, 1.3.1].
• Skin reactions: Skin rashes, itching (pruritus), hives (urticaria), and redness (erythema) are very common [1.3.1, 1.3.4]. Skin disturbances are the most frequent type of allergic reaction [1.3.5].
• Neurological symptoms: Dizziness, headache, and drowsiness are also frequently reported [1.3.4, 1.3.5].
• General malaise: Symptoms like fatigue and fever can also indicate an ADR [1.3.4].

Severe and Life-Threatening ADRs

While less common, some ADRs are medical emergencies that require immediate attention. These reactions can result in hospitalization, permanent disability, or even death [1.5.1].

Anaphylaxis

Anaphylaxis is a rare but severe, life-threatening allergic reaction that can occur within minutes of taking a drug [1.6.2, 1.6.4]. It causes the immune system to release a flood of chemicals that can send the body into shock [1.6.4].

• Symptoms Include:
  • Tightening of airways and throat, causing difficulty breathing or wheezing [1.6.2]
  • Swelling of the lips, tongue, or face [1.4.2, 1.6.1]
  • A sudden drop in blood pressure (hypotension) [1.6.4]
  • A weak, rapid pulse [1.6.2]
  • Skin rash, hives, and itching [1.6.4]
  • Nausea, vomiting, or diarrhea [1.6.2]
  • Dizziness, fainting, or loss of consciousness [1.6.2]

Severe Cutaneous Adverse Reactions (SCARs)

This group of reactions involves severe skin damage.

• Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN): SJS and the more severe TEN are rare disorders usually caused by a reaction to medication [1.7.1]. They begin with flu-like symptoms (fever, sore mouth and throat, fatigue) followed by a painful red or purple rash that spreads and blisters [1.7.1, 1.7.2]. The top layer of the affected skin then dies and sheds [1.7.1]. These conditions are medical emergencies requiring hospitalization [1.7.2].
• Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS): This reaction can appear 2 to 8 weeks after starting a drug and involves a widespread rash, fever, swollen lymph nodes, and inflammation of internal organs like the liver, heart, or lungs [1.4.1].

Organ-Specific Damage

• Drug-Induced Liver Injury (DILI): This can range from mild, asymptomatic cases to severe liver failure. Symptoms include jaundice (yellowing of skin and eyes), dark urine, fatigue, nausea, and pain in the upper right abdomen [1.8.2, 1.8.3, 1.8.1].
• Drug-Induced Kidney Injury (Nephritis): Symptoms can include fever, blood in the urine, general swelling, and confusion [1.4.1].

Comparison Table: Mild vs. Severe ADR Symptoms

Symptom Category	Mild/Moderate Reaction Examples	Severe/Life-Threatening Reaction Examples
Skin	Localized rash, itching, mild hives [1.3.1]	Widespread blistering rash, skin peeling (SJS/TEN), extensive hives [1.7.1, 1.4.2]
Respiratory	Runny nose, cough [1.4.1, 1.3.2]	Wheezing, shortness of breath, tightening of the throat (anaphylaxis) [1.6.2]
Cardiovascular	Rapid heartbeat (tachycardia) [1.3.4]	Sudden drop in blood pressure, weak and rapid pulse, loss of consciousness [1.6.2]
Gastrointestinal	Nausea, mild diarrhea, stomach upset [1.3.5]	Severe abdominal cramps, persistent vomiting or diarrhea [1.6.1]
General	Fatigue, low-grade fever [1.3.4]	High fever with rash, general swelling, feeling of impending doom [1.4.1, 1.6.5]

Risk Factors for Adverse Drug Reactions

Several factors can increase a person's risk of experiencing an ADR:

• Age: Older adults and very young children are more susceptible [1.11.3]. Older adults often have multiple health issues and take several medications (polypharmacy) [1.11.1].
• Polypharmacy: The use of multiple drugs increases the risk of drug interactions and ADRs [1.11.1].
• Genetics: Inherited genetic variations can affect how the body metabolizes certain drugs [1.11.3].
• Pre-existing conditions: Impaired kidney or liver function can alter how a drug is cleared from the body [1.11.1].
• Gender: Women may be more susceptible to certain types of ADRs [1.11.2].

What to Do and How to Report

If you suspect an ADR, contact a healthcare provider immediately. For severe symptoms like trouble breathing or swelling of the face, seek emergency medical care [1.3.2]. It is also vital to report ADRs. In the United States, patients and healthcare professionals can report adverse events to the FDA's MedWatch program. This can be done online, by phone, or by submitting a form [1.9.3, 1.9.4]. Reporting helps the FDA monitor the safety of products on the market.

Visit the FDA's MedWatch reporting page

Conclusion

Understanding the potential symptoms of an adverse drug reaction is a fundamental aspect of medication safety. Symptoms can vary widely, from a mild, temporary rash to a life-threatening emergency like anaphylaxis or Stevens-Johnson syndrome. Knowing your risk factors, recognizing warning signs, and communicating promptly with a healthcare professional are essential steps. Reporting suspected ADRs is a critical action that contributes to the safety of medications for everyone.

Frequently Asked Questions

What is the difference between an adverse drug reaction and a side effect?

An adverse drug reaction (ADR) is a harmful and unintended response to a medication used at a normal dose, such as an allergic reaction [1.10.2]. A side effect is a known, secondary effect of a drug that is not the primary therapeutic purpose, like drowsiness from an antihistamine. Side effects are often predictable, whereas many ADRs are not [1.10.3].

How quickly can an adverse drug reaction occur?

An adverse drug reaction can happen very quickly, within minutes to an hour after taking a drug, especially in the case of severe allergic reactions like anaphylaxis [1.4.1, 1.6.2]. However, other reactions, particularly skin rashes, can be delayed and may not appear for hours, days, or even weeks [1.4.1].

What are the most common symptoms of an ADR?

The most commonly reported symptoms include skin issues like rash, hives, and itching, as well as gastrointestinal problems like nausea, vomiting, and diarrhea. Dizziness and headache are also common [1.3.4, 1.3.1].

What is anaphylaxis?

Anaphylaxis is a rare, severe, and potentially fatal allergic reaction. Symptoms include difficulty breathing due to throat and airway constriction, a rapid and weak pulse, a sudden drop in blood pressure, hives, and swelling of the face or tongue. It is a medical emergency that requires immediate treatment [1.6.2, 1.6.4].

Can an ADR develop even if I've taken the drug before without any problems?

Yes. Your body can develop a sensitivity to a drug over time. You might not have a reaction the first time you take a medication, but your immune system can develop antibodies that trigger a reaction on subsequent exposures [1.6.3].

What should I do if I think I'm having an adverse drug reaction?

If you experience mild symptoms, you should contact your healthcare provider for advice. If you have severe symptoms like trouble breathing, widespread rash with blisters, or swelling of your face or throat, you should seek emergency medical care immediately [1.3.2].

How can I report an adverse drug reaction?

In the United States, patients and healthcare providers can report adverse drug reactions to the FDA through the MedWatch program. You can submit a report online, by phone (1-800-FDA-1088), or by mail using a specific form [1.9.3, 1.9.4].