Canadian researchers are calling for changes to guidelines on Diclectin, one of the most commonly prescribed drugs for morning sickness, after it was discovered that the drug isn't associated with a reduced risk of birth defects despite previous research claims.

In a commentary published Tuesday in the Journal of Obstetrics and Gynaecology Canada, Canadian researchers examined the data on pyridoxine-doxylamine.

Pyridoxine-doxylamine, known in Canada as Diclectin, is commonly prescribed to pregnant women to help manage nausea and vomiting during their first trimester. It has been prescribed to 33 million women worldwide since the 1950s, and is used in about half of all Canadian pregnancies that result in a live birth.

The Society of Obstetricians and Gynecologists of Canada lists the drug as the "standard of care" for pregnant women with morning sickness.

But despite its regular use in Canada, St. Michael's Hospital family physician Dr. Nav Persaud found himself questioning the drug after speaking with a patient about it.

"When prescribing the drug to one of my patients she had a lot of questions," Persaud said in a statement. "I found myself making strong statements about its safety and realized that I should know more."

This led Persaud to go through Diclectin's safety data.

As he went back and sifted through the research, he found that the number of patients that took part in the original studies on the drug -- numbers commonly cited by doctors and health agencies -- was actually lower than what was initially reported.

Close to 130,000 patients took part in those original studies, not more than 200,000 as was previously stated in a 1997 meta-analysis, he found.

As well, the drug was also incorrectly reported as being associated with a decrease in the risk of birth defects, such as limb malformations and congenital heart defects, he said.

"The numbers didn't add up," Persaud said. "Despite claims that it reduced the risks of birth defects, data was much closer to natural average of birth defects – between three and five per cent of all pregnancies."

The guidelines on the drug's use should be changed in light of this new knowledge, Persaud said, particularly because there are other anti-nausea alternatives available to pregnant women.

One of these alternatives, pyridoxine without doxylamine, has stronger safety data and is frequently prescribed in other countries, he said.

However, Persaud said that none of the treatments prescribed for morning sickness are overly effective. As well, all of them carry their own small risks.

"No medication is completely safe," he told in a telephone interview. "You always have to weigh the benefits versus the risk, and overall none of these medications are very effective.

"Nausea and vomiting in pregnancy is a self-limited condition, in most cases it gets better without any treatment. And the added benefit of taking Diclectin versus waiting or using lifestyle measures is quite small, and that's the case with all of these treatments," he said.

Persaud said he'd like the Canadian guidelines to more closely resemble those from other countries that first recommend lifestyle modifications to combat morning sickness, such as eating small meals. He also thinks Diclectin should not be considered the first-line treatment.

"There are a number of other medications and treatments that are reasonable options for nausea and vomiting in pregnancy, and in my opinion they are better options," he said.

Persaud said he's already changed his own practice, and now recommends his patients try alternatives, including vitamin B6.