The signs of an allergic reaction can range from mild to life threatening. Some allergic reactions can occur without any previous symptoms of an allergy. Make sure you talk to your doctor or pharmacist right away if you experience anything unexpected after starting a new medication.

Most allergic reactions occur within one hour of taking the medication, and involve the following common signs and symptoms:

• hives (itchy, slightly red and swollen patches on the skin)
• skin rash
• itching of the lips, tongue and/or face
• sensitivity of the skin to sunlight (an itchy and scaly rash when skin is exposed to sun)

Within 1-2 weeks of taking a medication, these additional signs and symptoms may be present:

• fever
• muscle and joint aches
• swollen throat glands (lymph nodes)
• changes in urine colour

Low blood pressure, wheezing, and other signs may indicate a potentially life-threatening reaction known as anaphylaxis (see "Types of drug allergy").