Long-term use of several common allergy medications could lead to severe itching in rare cases, the U.S. Food and Drug Administration warns.

The itching is called “pruritus,” and it can be caused by over the counter or prescription forms of Zyrtec (cetirizine) or Xyzal (levocetirizine), both antihistamines that treat seasonal allergies. It typically occurs within a few days of stopping the medications, the FDA said.

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People who take the oral medications every day for months or years may be susceptible to the condition in exceptional cases, the administration stated in an alert this month.

“Reported cases were rare but sometimes serious, with patients experiencing widespread, severe itching that required medical intervention,” the administration said.

The FDA reported finding 209 cases worldwide, between 2017 and 2023, in people who stopped using the two medications.

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“Most patients who experienced pruritus after medicine discontinuation reported using these medicines for more than 3 months; however, some experienced this reaction after less than 1 month of use,” the administration said. Restarting the medication and then tapering it resolved the itching problem in most people, the FDA stated.

A warning will be added to the medications. Patients using the medications long-term should check with their health care provider about whether to continue.