Health Canada has ordered a drug for attention deficit hyperactivity disorder be taken off the shelves after learning it has been linked to 20 sudden deaths and 12 strokes in the U.S.

The drug in question is Adderall XR. It's made by Shire Biochem Inc. and was approved for sale in Canada just over a year ago. Prescriptions have been issued for about 11,000 Canadians since then.

Shire maintains the drug is safe, and Health Canada's decision to suspend sales is at odds with the U.S. Food and Drug Administration. The drug remains on the market in the United States with a revised warning label, saying it should not be used in patients with heart problems.

But Health Canada is asking people taking Adderall XR or parents of children on it to consult their physicians immediately to select alternatives.

As well, manufacturers of other related drugs for ADHD have been asked by Health Canada to provide a thorough review of their worldwide safety data.

People taking related ADHD drugs should not stop their treatment but could consult their doctors if they have concerns, the department said.

None of the deaths or strokes associated with Adderall XR were reported in Canada, said department spokesman Ryan Baker.

But he noted the agency has received eight reports of adverse reactions ranging in severity from convulsions to minor skin rash. "It's not been determined yet whether these reactions were a result of Adderall XR use,'' he said.

Shire's chief executive, Matthew Emmens, said in a statement late Wednesday that the company "remains confident in the safety and efficacy" of the drug. The company also said it "strongly disagrees with the conclusions drawn by Health Canada.''

Of the 20 cases of sudden death linked to the drug, 14 were in children. Two of the 12 strokes were suffered by children taking the drug.

Dr. Robert Peterson, director general of the Therapeutic Products Directorate noted that most of the victims had had no history of cardiac problems before their sudden deaths.

"The adverse events that were identified are very rare, but they are also catastrophic,'' he said in a conference call.

He also noted that the deaths occurred in patients who were taking the prescription as directed, within the recommended dosage levels.

Adderall is a stimulant within the amphetamine family. Peterson says the mechanism by which the drug causes adverse effects is not yet known but will be the subject of further investigation.

Health Canada began a review the drug's safety data in November 2004 following international reports of adverse reactions. They also chose to conduct a preliminary review of safety data for the other related drugs for ADHD treatment in Canada.

In the U.S., a related immediate-release form of the drug, called simply Adderall, is also available. But it has never been approved for sale in Canada.

The U.S. Food and Drug Administration said it had evaluated the same reports as Health Canada but doesn't believe the data warranted the same action in the United States.

"At this time, FDA cannot conclude that recommended doses of Adderall can cause sudden unexplained death, but is continuing to carefully evaluate these data,'' the agency said on its website.