Drug Allergies: Do Symptoms Show Right Away?

In our latest question and answer, the pharmacist discusses whether or not allergy symptoms show right away after taking a drug.


If I'm allergic to a drug, would I show symptoms right away?

Asked by May On Mar 16, 2018

Answered by
Medical Content Reviewed By PharmacistAnswers Staff

On Mar 17, 2018

An allergic reaction can be caused by any medication you ingest or even come in contact with. Although symptoms of an allergic reaction to a medication can manifest soon after taking or coming into contact with it, this is not always the case.

Some allergic reactions happen only after the medication has built up to certain levels in your system or after many exposures to the medication.

Lastly, some allergies can manifest later in life, to medication you weren't initially allergic to.  In addition, some individuals can often "outgrow" allergies they may have had as children or earlier in life.

To sum it all up:

  • Some allergies occur almost immediately after consuming or coming into contact with an offending medication.
  • Other allergic reactions are delayed and can happen days later.
  • You can develop allergies later in life to medication you were not previously allergic to.
  • You can "outgrow" allergies you had earlier in life.

It is possible to allergic to any medication.  The most common drug allergy is with penicillin, with allergies being reported in nearly 10% of individuals. Other commonly reported drug that induce allergic reactions include:

  • Aspirin
  • Opioids
  • Amoxicillin
  • Ibuprofen
  • Naproxen
  • Sulfamethoxazole 

Types Of Drug Allergies

A drug allergy occurs when the immune system identifies the drug taken as a foreign or threatening substance. Our bodies release chemicals that cause allergy symptoms, which can sometimes be severe (as discussed below).

Allergic reactions have different classifications and are often grouped by how quickly they occur:

Type I Drug Allergy Reactions

Type I drug allergies generally occur within 72 hours of taking a medication you are allergic to. A severe reaction, that occurs almost immediately after taking a medication, is known as anaphylaxis. Anaphylaxis can be extremely serious and requires immediate medical attention. Signs of anaphylaxis include:

  • Swollen throat
  • Hives
  • Wheezing
  • Chest tightness
  • Trouble breathing

Late Drug Reactions (Type II, III, IV)

Late drug reactions typically occur more than 72 hours after taking a dose of a medication. Late drug reactions can be mild in nature (e.g. rash, itching) or can be serious (e.g. serum sickness).

Drug Allergy Symptoms

Allergies to medication can manifest as a wide variety of symptoms, regardless when they occur. You should seek medical attention immediately if you are experiencing any severe symptoms or if any of the mild symptoms seem to be getting worse or are interfering with quality of life. 

Examples of mild allergy related symptoms include:

  • Itching
  • Rash
  • Hives
  • Swelling
  • Itchy, watery eyes
  • Fever

Examples of more severe allergy related symptoms can include:

  • Shortness of breathe/trouble breathing
  • Swelling
  • Nausea
  • Dizziness
  • Diarrhea
  • High heart rate
  • Low blood pressure

About the Pharmacist

Dr. Adam DeRue Pharm.D

Dr. Adam DeRue is a Doctor Of Pharmacy and registered pharmacist.

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