An allergic reaction is an immune system response to a trigger, called an allergen. The immune system protects the body from germs and other invaders. But sometimes it reacts too strongly and causes an allergic reaction.
Medicines, pollen, certain foods, pets, insect stings, and other substances can cause allergic reactions. A drug allergy is a potentially harmful immune system reaction to a medicine. Many medicines can cause an allergic reaction, but it is more common with certain types of medicines. These include antibiotics, pain relievers like nonsteroidal anti-inflammatory drugs (NSAIDs), and some chemotherapy.
Most allergic reactions are mild and can be treated with over-the-counter medicines, such as antihistamines, which work by blocking the body’s allergic response.
Severe allergic reactions can be life-threatening and need immediate medical treatment. Families should know the symptoms of allergic reactions and have a plan for emergencies. Avoiding allergens can help prevent future reactions.
Symptoms of an allergic reaction to medicine
Drug allergy signs and symptoms can range from mild to severe and may worsen over time. Symptoms of a mild allergic reaction can include:
Localized skin redness, rash, hives or itching
Itching of the eyes, tongue, or throat
Runny nose, sneezing, or watery eyes
Nausea, vomiting, or diarrhea
Contact your health care provider for instructions, even if symptoms appear mild.
Anaphylaxis symptoms
A drug allergy can cause a serious, life-threatening reaction called anaphylaxis. Symptoms of anaphylaxis may include those listed above but may also include:
Extensive skin reactions, such as rashes covering large amounts of the body, blistering or peeling of the skin
Pale or blue skin
Swelling of the mouth, tongue, lips, throat, or eyes
Coughing, wheezing, shortness of breath, or trouble breathing
Trouble swallowing
Low blood pressure (feeling faint or dizzy)
Fast or weak heart rate
Confusion, decreased alertness, or loss of consciousness
Seek emergency help right away if your child has signs of anaphylaxis.
Steps to take if your child has a severe allergic reaction
Discuss an allergy action plan with your care team. If appropriate, always keep epinephrine with you or your child, and make sure family and friends know how to use it in an emergency.
If your child has symptoms of a severe allergic reaction, seek medical care right away. Severe allergic reactions can lead to death. Do not wait to see if symptoms get better or worse.
Steps to take during a severe allergic reaction:
Give epinephrine immediately, if available.
Call for emergency medical services right away (911 in the U.S.).
Monitor your child’s pulse, breathing, and alertness until help arrives. If your child becomes unresponsive, start CPR.
Always seek medical care after a severe reaction or if you give epinephrine. It is important to monitor symptoms and make sure the reaction is completely gone.
How to prevent allergic reactions to medicines
Work with your care team to identify, prevent, and treat drug allergies.
To identify medicine allergies, your health care provider or pharmacist will ask questions such as:
What were your child’s symptoms?
When did the reaction occur?
Have your child’s medicines changed?
What medicine caused a previous reaction?
Does anything make it better or worse?
To prevent drug allergies:
Work with your health care provider to make sure your child’s medicine list is up to date with all medicines and known allergies.
If your child has a known drug allergy, be aware that related medicines might cause similar reactions
Let all health care providers know about the medicines your child takes. This includes over-the-counter medicines, vitamins, and supplements.
Watch for symptoms of an allergic reaction, especially when starting a new medicine.
If your child has a drug allergy, your care team can:
Stop the medicine that causes the reaction
Change the medicine dose or type
Add medicines to ease allergy symptoms
Always talk to your health care provider before making changes to your child’s medicines.
Common questions about drug allergies
What medicines are most likely to cause an allergic reaction?
Any type of medicine can cause an allergic reaction. But some have a higher risk. These include:
Genetic traits that affect how the body responds to medications (pharmacogenetics)
A history of other allergies, such as to medications, foods, or environmental triggers
Being young or middle-aged
Being female
Having certain health conditions, such as asthma or autoimmune disorders, might also increase the risk of drug allergy.
Can a drug allergy develop at any time?
Yes. Some people react after the first dose. Other people react after several doses.
Can someone “grow out of” a drug allergy?
Yes, in some cases, a person can become less sensitive to a medicine over time, but this is rare. A health care provider or pharmacist can answer questions about whether your child’s medicine allergies may change. If your child has had an allergic reaction to a medicine, consider seeing an allergist or immunologist before taking the medicine again.
How long does it take for a reaction to occur after taking a medicine?
Most allergic reactions occur within hours of taking the medicine. In rare cases, they may occur later. To identify what caused the allergic reaction, your care team may ask:
When the reaction happened
If the medicine is known to cause allergic reactions
What happened when your child stopped or restarted the medicine
If there are other possible causes
What is anaphylactic shock?
Anaphylactic shock is a severe allergic reaction that can cause the body to go into shock. As the body reacts to the allergen, the blood vessels become wider. When this happens, the blood pressure drops. Blood flow is reduced, and cells do not get enough oxygen, especially in the brain. Anaphylaxis can be fatal without immediate treatment.
Tips for families
Make an action plan and share it: Have a plan with steps to take during an allergic reaction. Keep a list of allergies, current medicines, and emergency contact numbers. Share the action plan with people at school, work, or other places your child spends time.
Wear medical identification: Patients at risk for severe allergic reactions should wear a medical ID bracelet or necklace. This helps emergency responders give care quickly.
Keep emergency supplies: Always carry epinephrine if needed. Teach family and friends how to use it in case of an allergic reaction.
What symptoms of a drug allergy should we watch for?
Could my child’s drug allergies change over time?
Should my child wear a medical ID bracelet or necklace?
Should I carry epinephrine?
What should I do if my child has an allergic reaction?
What emergency warning signs should we watch for?
Key points about allergic reactions to medication
A medicine or drug allergy happens when the immune system mistakenly sees a medicine as harmful and reacts against it.
Allergic reactions can be mild or severe. Mild reactions sometimes can be treated with over-the-counter medicines. Severe reactions can be life-threatening and need immediate medical care.
Symptoms of an allergic reaction include rash, hives, itching, shortness of breath, coughing, tightness in the throat, and swelling of the face or neck.
Families should have an allergy action plan. Keep a list of your child’s medicines, allergies, and emergency contact numbers.
People at risk for severe allergic reactions should carry epinephrine and wear a medical bracelet or necklace.
Talk to your health care provider or pharmacist if your child has any signs or symptoms of a drug allergy.
Side effects are unintended effects or unwanted symptoms that occur because of medicines or other treatments. Learn how to manage and cope with side effects.
