Dr. Jennifer Blake said women who have been taking the birth-control pill Freya-28 in the last few months should speak to their doctors and temporarily use an additional method of contraception, such as a condom.
On Tuesday, Health Canada issued a notice of recall for Freya-28 after a pharmacy reported that a package had been found that contained a placebo pill in place of an active one.
Packages of the pills sold by Mylan Pharmaceuticals should have 21 white pills containing active ingredients, laid out in three rows, and a single row of seven green placebo pills.
Two lots of the product that were sold across Canada — 3739F001B and 3739F002B — have been recalled. The company's other birth-control product, Freya-21, is not affected.
The lots contained a total of more than 79,500 individual blister packs of the 28-day contraceptive, company spokeswoman Nina Devlin confirmed Wednesday. Almost 76,300 of those had been distributed country-wide between May 10 and Aug. 22, when the packaging mix-up was reported to the company.
The drug, a generic version of the brand-name contraceptive Marvelon, is packaged for Mylan by Famy Care Ltd., a Mumbai-based pharmaceutical company.
Health Canada said missing one or more active pills could reduce the contraceptive's effectiveness and result in an unplanned pregnancy.
Blake said the risk of conception depends on when in a woman's menstrual cycle the extra placebo pill might have been taken.
"So if you missed a pill at the very beginning or at the very end — if that was the pill that was incorrect, towards the beginning or the end — then that means instead of having seven days of placebo pills, you've had eight days of placebo pills," she said Wednesday from Ottawa.
"And that's assuming that that was the only error in this batch."
Missing a pill containing active ingredients at a critical point in a woman's cycle could allow an egg to escape, and ovulation and conception to occur, Blake said.
"If it's absolutely smack, plum in the middle of the month, then the chances are that you're going to be OK — but we don't know."
Women using birth control pills take the drugs for 21 days of each menstrual cycle. Because of the risk that they might not remember to resume taking their pills at the right time, many oral contraceptives are packaged with a pill for each of the 28 days in a cycle — 21 are drug and seven are placebo.
The Freya-28 recall is the second for an oral contraceptive this year. In April, Alysena 28 was pulled from the market when it was discovered one lot contained too little active drug and too much placebo, leaving women who took it vulnerable to becoming pregnant.
The lot sold by generic drug maker Apotex contained about 50,000 faulty packets, which were sold across Canada.
"I was so disturbed to see that this had happened again," said Blake, calling it "twice too often."
Consumers using Freya-28 can return unopened packages to their pharmacists and are asked to report any adverse reactions potentially related to recalled pills to Health Canada. As of Tuesday, Mylan said no adverse effects had been reported.