Why Stop Taking Antihistamines Before Allergy Testing

Why You Should Stop Taking Antihistamines Before Allergy Testing

If you are scheduled for an allergy test, talk to your provider about stopping certain medications beforehand to ensure the most accurate results. One of the most common medications patients forget to pause is over-the-counter (OTC) antihistamines, including Benadryl® (diphenhydramine), Claritin® (loratadine), Zyrtec® (cetirizine), and Allegra® (fexofenadine).

Board-certified allergy specialist, Katherine McCormack, MD, explains why these medications can interfere with your test results and how to prepare for a visit to the allergist.

What Antihistamines Do?

Antihistamines block the effects of histamine, a chemical your immune system releases during an allergic reaction. By reducing histamine activity, they help relieve symptoms such as:

• Sneezing and nasal congestion
• Itchy or watery eyes
• Skin rashes and hives

While this helps with day-to-day allergy management, it can complicate allergy testing.

How Antihistamines Interfere with Allergy Testing

Allergy skin testing works by introducing tiny amounts of common allergens into the skin to see how your body reacts. If you are allergic, your immune system releases histamine, creating a small red bump or itch at the test site. However, if you’ve recently taken an antihistamine, the medication suppresses this histamine response. This can lead to false-negative results, meaning your test might not accurately identify what you’re allergic to.

Discontinuing antihistamines is crucial before testing, as it allows your allergist to develop an effective treatment plan that may include allergy immunotherapy, lifestyle changes, or medication management.

When to Stop Taking Antihistamines Before Testing

Most antihistamines should be discontinued five to seven days before your appointment, but timing can vary by type and how long they stay in your system.

Your Boulder Medical Center allergy provider will give you personalized instructions and review your full medication list. Always check with your provider before stopping any prescribed medication.

Hidden Sources of Antihistamines

Many products contain antihistamines without patients realizing it. Common examples include:

• Cold and flu medications
• Sleep aids
• Some heartburn and stomach relief medications

It’s a good idea to give your allergist a list of everything you’re taking, including supplements and over-the-counter products, so your provider can review for hidden antihistamines.

Let’s Talk 

If you are scheduled for an allergy test, talk to your provider about stopping certain medications beforehand to ensure the most accurate results. If you are in or near Boulder County, you can schedule testing with our Allergy Team in Boulder or Louisville, CO.