Canadian regulators have suspended sales of the once-daily version of Adderall, a popular drug used to treat attention deficit hyperactivity disorder (ADHD). Health Canada said the drug carries a risk of sudden death in children. Later, the U.S. Food and Drug Administration (FDA) issued an advisory about the drug.

"Health Canada has suspended the market authorization of the product due to safety information concerning the association of sudden deaths, heart-related deaths, and strokes in children and adults taking usual recommended doses of ADDERALL and ADDERALL XR," the agency said in a statement.

Health Canada said its decision came as a result of a review of safety information provided by the manufacturer, which indicated there were 20 international reports of sudden death in patients taking either ADDERALL or ADDERALL XR.

"These deaths were not associated with overdose, misuse or abuse. Fourteen deaths occurred in children, and six deaths in adults. There were 12 reports of stroke, two of which occurred in children. None of the reported deaths or strokes occurred in Canada," the agency said.

The FDA said it has examined the same study data as the Canadian health authorities but had not concluded the risk of sudden death was "strong enough" to justify suspending sales of the drug.

The FDA's advisory said only that Canada had suspended all sales of the Shire Pharmaceutical Group medication, which is used by 700,000 Americans.

Shire said there have been 20 reports of sudden deaths by Adderall users since the drug was introduced in Canada in 1994. The company said the deaths were "extremely rare" and noted that more than 38 million prescriptions have been filled.

Shire said it "steadfastly disagrees" with the Canadian health authority's decision.

But Health Canada said a review of safety data for other stimulants authorized for use in the treatment of ADHD in Canada indicated that, "The incidence of serious adverse reactions leading to death was higher in ADDERALL and ADDERALL RX combined than in the other drugs of this class."

The FDA sought stronger warnings on the drug's labels after it studied the same statistics reviewed by Canada. But Health Canada, in its suspension letter, said the risk of sudden death "cannot be managed by label changes."

Health Canada said patients taking drugs of the same class for the management of ADHD should NOT discontinue their medication, and should consult with their physician if they have any concerns or questions.

Health Canada also said that consumers should not flush unused drugs down the toilet or sink to avoid contaminating ground or municipal water systems but should return any unused product to their pharmacy.