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Canada's obstetricians say a study showing how a popular pain reliever can turn a mother's milk into a toxic brew for newborns has raised warning bells, with one doctor asking the country's busiest maternity hospital to yank the product off its shelves.

"My suggestion is that all obstetric units across this country remove T3s [Tylenol 3] from their obstetric formulary," said perinatologist Peter von Dadelszen, associate professor of obstetrics and gynecology at the University of British Columbia.

"... I've actually contacted the hospital leadership [at BC Women's Hospital] asking that it be yanked completely so we no longer have it available."

Also yesterday, the Society of Obstetricians and Gynaecologists of Canada said it will meet next week with the Canadian Pediatric Society to discuss the best and safest pain relief for nursing mothers - with an eye to having a guideline on the subject by 2009, said its executive vice-president, André Lalonde.

"We don't want to panic people here. There's kind of a warning bell going out there, but we need a lot more studies to see it," Dr. Lalonde said in an interview from Ottawa. "The general advice is to take the smallest dose possible."

The reactions follow a study by Gideon Koren, Parvaz Madadi and colleagues showing how nearly one-quarter of babies whose mothers took codeine while breastfeeding showed signs of central nervous system depression, such as sedation or abnormal breathing.

Tariq Jamieson died in 2005 at 12 days old of a morphine overdose he got through his mother's breast milk.

Rani Jamieson, an accountant in Toronto, had been prescribed codeine after she gave birth. She later learned that she carried multiple copies of a gene capable of converting the common pain reliever into strong concentrations of morphine.

The Jamieson case was thought to be a rare pharmacological phenomenon; however, in the new study, 17 of 72 newborns showed symptoms of central nervous system depression, leading researchers to conclude it occurs more frequently.

That has led Dr. Koren, director of the Motherisk Program at the Hospital for Sick Children in Toronto, to conclude that codeine as a treatment for mothers cannot be considered safe for all breastfed infants.

Codeine is made by several drug companies, and is contained in Tylenol 3. The pain reliever, Dr. Koren estimates, is prescribed to as many as 120,000 Canadian women a year after childbirth.

Shellie Suter, spokeswoman of Janssen-Ortho Inc., which markets the drug in Canada, said the company could not comment on the study as it has not had time to review it sufficiently.

"The safety of patients who use our products is a priority for the company," Ms. Suter wrote in a prepared statement. "TYLENOL 3 (prescription Tylenol with codeine) is a safe and effective product when used according to the approved prescribing information."

Canadian pharmacies dispensed more than 5.3 million prescriptions for the codeine-and-acetaminophen combination pills last year, according to IMS Health, a private health-information and consulting-services company. Prescriptions for the drug have fallen slightly, with 5.4 million prescriptions filled in 2006 and 5.6 million in 2005.

No professional organization in Canada has guidelines on breastfeeding and codeine, but the American Academy of Pediatrics recommends it as compatible with nursing.

That guideline was already being revisited before the Clinical Pharmacology & Therapeutics study was published on Wednesday.

Now, experts are taking a closer look at it, said Ruth Lawrence, chairwoman of the section on breastfeeding for the American Academy of Pediatrics.

"This recent revelation about codeine is of concern because codeine has always been pretty much treated rather casually," Dr. Lawrence said in a telephone interview from Rochester, N.Y.

"... Probably the best advice to people is to be very cautious about using compounds that contain codeine."

Ruth Wilson, who is president of the College of Family Physicians of Canada and still delivers babies, said she rarely prescribes codeine to mothers.

"In my own practice if someone needs codeine, I think hard about it and make sure there is no other cause for that amount of pain," Dr. Wilson said. "In my own clinical experience, they [new mothers] can manage without it."

Health Canada has said it is studying proposed labelling changes that better identify the potential risk to nursing children from codeine in breast milk.

Codeine is rarely dispensed to mothers after childbirth in Europe, Britain or New Zealand, said Dr. von Dadelszen of BC Women's Hospital. He said other drugs can be used for pain relief.

Two years ago, he and others lobbied to tighten access to codeine at his hospital so that a specific order has to be made to prescribe it. (It no longer comes through regular postpartum orders.)

Yesterday, he pushed the issue further, asking hospital management to remove it for use after childbirth.

"Why use a constipating compound that relieves very little extra pain and is potentially dangerous for babies," Dr. von Dadelszen asked. "It has had tragic consequences in this country."