(HealthDayNews) — Allergic reactions to medications can occur with drugs you’ve taken before without incident — or to a drug that your doctor hasn’t prescribed to you before.

According to Health Canada, most allergic reactions occur within one hour of taking the medication.

Signs of an allergic reaction include:

• Hives, which are itchy, red and swollen patches on the skin.
• A skin rash.
• Itching of the lips, tongue and possibly face.
• Sensitivity of the skin to sunlight.

If you experience anything unexpected after starting a medication, tell your doctor immediately.