Drug Reactions Differ From Side Effects

Before prescribing any drug for our patients--even over-the-counter products--we always ask first if they are allergic to any medications. Many patients think they are, because of adverse reactions they’ve experienced while taking drugs. Studies show, however, that only about 10% of their reactions are really caused by an allergy.

Allergic drug reactions occur when your body’s immune system reacts inappropriately to a medication. The role of the immune system is to recognize harmful foreign substances (like viruses and bacteria) and eliminate them from your body. Unfortunately, it occasionally responds to medications this way (the risk of an allergic reaction for most drugs is 1% to 3%).

Drug allergies can affect any organ in the body. Allergic reactions involving the skin are the most common and the easiest to recognize. Rashes due to drug allergy are generally red and raised and can appear on almost any area of your body. Raised welts, or “hives,” are another common manifestation of a drug allergy. An allergic reaction can also cause your hands, feet, face or lips to swell temporarily. Although the swelling is upsetting and uncomfortable, it is generally not dangerous.

Allergic reactions less frequently affect internal organs, including the liver (resulting in hepatitis), the gastrointestinal tract (producing cramps and diarrhea) and the brain (triggering seizures). In cases of severe allergy to a medication, a life-threatening reaction known as anaphylaxis can occur. Blood vessels throughout the body dilate, causing a dangerous fall in blood pressure, and the throat and airways frequently swell, making it difficult to breathe.

Allergic reactions generally occur shortly after you have started taking a new medication. The possibility of an allergic reaction should be the first thing you and your doctor think of whenever adverse symptoms appear after a medication is prescribed. You can also develop an allergy to a medication you have been taking for a long time, although this occurs much less commonly.

It is important, although sometimes difficult, to differentiate a drug allergy from a drug side effect, because the two are treated differently. A side effect is an undesirable consequence of the way a drug works in your body. For example, aspirin prevents heart attacks by interfering with the ability of your blood to clot. But this also makes you more prone to bleed, so a bloody nose is considered a side effect of taking aspirin.

Although bothersome, side effects of most medications are usually not dangerous and can often be controlled by adjusting the dosage of the drug or switching to a similar alternative drug. Usually, your doctor will be able to distinguish an adverse side effect to a drug from an allergic reaction by reviewing your medical history and examining you. In some cases, skin testing may aid in the diagnosis.

Because a drug allergy can have very serious consequences, the most important step to take after recognizing the problem is to discontinue the medication. Allergic symptoms usually subside without further treatment once the drug is stopped, although it may take several days for that to happen. However, do not stop taking a prescribed medication without informing your physician. Your doctor will almost always be able to prescribe an alternative medication.

In the event of an anaphylactic reaction to a drug, you should seek emergency medical attention immediately, and a medication called epinephrine must be administered as quickly as possible.

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Here are some steps you can take to reduce your risk of experiencing a drug reaction:

Minimize the number of medications you take. Take medications only when they are absolutely necessary. Cholesterol-lowering medications, for example, should be used only when dietary changes fail to bring cholesterol levels under control.

Maintain a complete list of the medications you use. Include the generic and brand name of each drug you take along with the dates that you take the medication. Keep a written record of any side effects or allergic reactions you have to each medication.

Make certain that your physician and pharmacist have a complete list of medications to which you are allergic. Share this list with any new physician you see. If you have a drug allergy, consider wearing a MedicAlert bracelet or necklace identifying all the medications to which you are allergic. This will prevent you from accidentally receiving any of those medications in the event of an emergency.

For more information, contact MedicAlert at (800) 633-4260 or https://www.medicalert.org.

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Dr. Jonathan Fielding is the director of public health and the health officer for the Los Angeles County Department of Health Services. Dr. Valerie Ulene is a board-certified specialist in preventive medicine practicing in Los Angeles. They can be reached by e-mail at [email protected].