Is It a Drug Allergy or a Side Effect?

Reviewed by Carol DerSarkissian on November 11, 2019

When you start a new medication, you might feel queasy, run a fever, or get a rash. Are you allergic to the medicine, or are these just normal side effects?

It's an important question to get answered, because drug allergies can be serious. But only a handful of bad reactions to medicine are due to an allergy.

Tell your doctor right away if you notice any of these warning signs.

Drug Allergy Symptoms

An allergy means your body sees the medicine as harmful. It rejects the drug with an allergic reaction. This may be mild or strong. It can happen a few hours after you take the drug or not until 2 weeks later.

Mild allergy symptoms are:

Severe allergy warning signs can include:

Is It a Side Effect?

These can seem like an allergic reaction, but it’s just your body feeling sensitive to a new medication. It shouldn’t be dangerous, although you may feel sick for a while.


If you take several drugs for different reasons, you may be more likely to have side effects.

You might or might not have problems with a new drug, but the most common ones include:

Ask your doctor or pharmacist what to expect from the new treatment. You can also find side effects listed on the printout that comes with it and inside the package.

What to Do

Call your doctor if you have any symptoms of a drug allergy. They'll probably tell you to come in for an exam or tests to see if you're allergic to the medicine.

If you are, your doctor will tell you to stop taking it right away. They may give you something to help your body fight the allergy so you feel better.

Let them know if side effects are making you ill. You may be able to take a lower dose of the drug. Or they can prescribe something to ease your trouble like an antacid to calm an upset stomach. They might switch you to a different drug.


If you’re older and you take more than one drug for different health problems, your body may have a hard time breaking them all down. Talk to your doctor about your risk of side effects and what you can do to ease them.

Always follow these tips when you get a new drug:

  • Tell your doctor about any drug reactions you've had in the past.
  • Tell them about all the drugs, supplements, or vitamins you take for any reason.
  • Ask your doctor or pharmacist if you should take your medication in a particular way, like with food.

If you do have a drug allergy, let any new doctors or nurses you see know about it. You can get a bracelet or a card to put in your wallet that lists your allergies. This could save your life if you have to go to the emergency room or hospital and you’re unable to talk.

WebMD Medical Reference



American Academy of Allergy, Asthma and Immunology. “Medications and Drug Allergic Reactions: Tips to Remember”

American Academy of Family Physicians. “Drug Reactions.”

National Institutes of Health Senior Health. “Taking Medicines: Side Effects”

UCLA Food and Drug Allergy Care Center: “Drug Allergy Questions and Answers”

Casillas A. American Family Physician. November 2003

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