Women who are pregnant or may become pregnant should avoid the wakefulness-promoting drug modafinil, sold as Alertec, to prevent serious harm to the fetus, Health Canada warns.

In a notice to health-care professionals on Thursday, Health Canada said Alertec has been associated with "cases of major fetal congenital malformations, including congenital cardiac anomalies."

The drug is sold in 100 mg tablets, including generic tablets, to treat adults with excessive sleepiness.

Modafinil is prescribed to treat sleepiness from conditions such as narcolepsy (which can manifest with sudden attacks of sleep that cannot be controlled), obstructive sleep apnea and shift work disorder.

Health Canada said findings from international reports showed Alertec may cause harm to an unborn baby. The regulator added:

Women who are pregnant, or plan to become pregnant, must not use Alertec.

Hormonal birth control methods, such as birth control pills, injections, implants, intrauterine devices or patches, may not work as well when used at the same time as Alertec. Women who use these types of birth control may have a higher chance of getting pregnant while taking Alertec, and for two months after stopping it. Patients should talk to a health-care professional about birth control methods that are right for them.

Women should take a pregnancy test within a week before starting treatment with Alertec and ensure they are not pregnant.

The drug is a non-amphetamine-based stimulant that is also used to treat attention deficit hyperactivity disorder.

When animal studies pointed to "developmental toxicity," the U.S. Food and Drug Administration asked the drug's maker, Teva Pharmaceutical Industries, for a registry of women taking the drug to shed light on pregnancy and fetal outcomes.

In February 2019, Teva Canada Innovation informed Health Canada of the results of its 2018 annual report from that registry for modafinil as well as armodafinil —​​​​​​ a similar medication not listed in Health Canada's database of drugs approved for sale in this country.

"The frequency of major congenital anomalies (17.3 per cent) and cardiac anomalies (4 per cent) associated with the exposure to modafinil and/or armodafinil was above the frequency observed in the general population (3 per cent and 1 per cent, respectively," Health Canada said in its letter on Thursday.

Since the drug went on sale, there have also been reports of congenital malformations and of low fetal growth, as well as cases of babies who demonstrated poor physical development, the regulator said.

In 2007, Health Canada also warned of serious skin and allergic reactions related to Alertec.

The earliest listing in the database for Alertec sales in Canada dates back to 1999.

Information on how widely used the drug is, including in pregnancy, is not readily available.