While anyone can have an allergic or nonallergic reaction to a drug, a few factors can increase your risk. These include:

  • Having a past allergic reaction to the same drug or another drug. Even if past reactions have been mild, you may still be at risk of a more severe reaction.
  • Taking a similar drug to one that caused a reaction in the past. For example, if you've had a reaction to penicillin, you also may be sensitive to some other antibiotics.
  • Having a weakened immune system from conditions such as the Epstein-Barr virus or HIV/AIDS.
  • Having a history of other allergies, such as hay fever.
  • Taking several drugs at the same time, or taking frequent doses of the same medication.

Those who have a greater risk of developing a more severe reaction to medications include people with:

  • Asthma
  • Heart disease
  • High blood pressure
Oct. 14, 2011

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