Drug allergies occur when the immune system has an allergic reaction to a medication. Common symptoms include hives, rashes, swelling of the face or lips, and wheezing. Many antibiotics like penicillin are common causes of drug allergies. Treatment focuses on relieving symptoms with antihistamines, corticosteroids, or epinephrine, and avoiding the drug in the future. While drug allergies cannot be prevented, knowing your allergies and avoiding triggering medications can help prevent dangerous reactions.