Signs and symptoms of a serious drug allergy often occur within an hour after taking a drug. Other reactions, particularly rashes, can occur hours, days or weeks later.

Drug allergy signs and symptoms may include:

• Rashes
• Itching
• Nausea
• Vomiting
• Diarrhoea (or occasionally constipation)
• Lethargy
• Headaches
• Blurred vision

All the known side effects from a drug are listed in the patient information guide that comes with the drug. These are listed in order of frequency (the most common will be first on the list).

Anaphylaxis from a drug allergy

Anaphylaxis is a rare, life-threatening reaction to a drug allergy that causes the widespread dysfunction of body systems. Signs and symptoms of anaphylaxis include:

• Tightening of the airways and throat, causing trouble breathing
• Nausea or abdominal cramps
• Vomiting or diarrhea
• Dizziness or lightheadedness
• Weak, rapid pulse
• Drop in blood pressure
• Seizure
• Loss of consciousness