Concordia has exclusive rights to market Ulesfia, a head-lice treatment. 

This story has been updated. 

The FDA issued a warning letter to Shionogi over its co-pay assistance program, telling the drugmaker that it omitted risk information about Ulesfia, a head lice treatment.

Shionogi had marketed a co-pay assistance voucher that claimed the drug is the number-one prescribed branded treatment for head lice. It failed, however, to provide any risk information about the benzyl alcohol formulation, according to the FDA’s Office of Prescription Drug Promotion.

Concordia Healthcare since 2013 has exclusively licensed the rights to Ulesfia. “We are working with Ulesfia’s NDA holder to address the FDA’s correspondence,” a spokesman for Concordia said in an email.

See also: Omitting risk info in ads is top reason for FDA warning

The voucher provided links to sites that published full prescribing information, but the regulator said that wasn’t enough.

“By omitting the risks associated with Ulesfia, the voucher fails to provide material information about the consequences that may result from the use of the drug and creates a misleading impression about the drug’s safety,” the FDA said.

Research conducted by Johnson & Johnson executives shows that about 60% of warning letters and untitled letters from 2013 to 2015 were issued because drugmakers failed to cite risk information in their promotional materials. Untitled letters are issued for less serious violations than warning letters.

The company has until April 13 to respond to the FDA.