People who regularly use the allergy medications Zyrtec or Xyzal may experience severe itching when they stop, the U.S. Food and Drug Administration said in a new warning.

Although the itching, called pruritus, is rare, the FDA said hundreds of people reported the condition after they stopped taking the medications cetirizine or levocetirizine daily for at least a few months.

In some cases, the itching got so bad it required medical attention, the FDA said.

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Now, the agency is reviewing the prescription version of the drugs to include a new warning about the severe itching risk, as well as requesting the manufacturers of the over-the-counter version to add a warning label.

Users who experience severe itching after stopping these medications should contact their health care professional, the FDA said.

The FDA also said if you are considering taking these allergy pills on a regular basis, consider this new risk and discuss it with your health provider beforehand.