OTTAWA -- Health Canada is advising consumers that it's received reports that some packages of the Alesse birth control pill that contain broken tablets or pills that are smaller than normal, potentially making the medication less effective.

The government says it's received complaints that in packages of both Alesse 21 and Alesse 28, there has been at least one pill that is roughly half the size of the others.

It says the reduced size may also reduce the medication's effectiveness at preventing pregnancy.

Health Canada says the complaints involved a package of Alesse 21, which contains 21 active birth control pills, that expires in August 2018, and a package of Alesse 28, which contains 21 active birth control pills and seven tablets that don't contain hormones, that expires in April 2019.

But the government says it's unsure whether the issue is isolated to those lots of pills, and it's working with Pfizer Canada to determine the scope of the issue.

Health Canada is advising consumers to check their pills before taking them, and not to take them if they look unusual, including a paler colour, jagged edges or a broken or smaller-than-normal tablet.

It advises consumers who find an odd pill not to take it, but to go to their pharmacy and get a replacement pack so they don't miss a day of the pill, which can increase the chance of pregnancy.

Health Canada is asking pharmacists to look at each blister pack of Alesse 21 and Alesse 28 before dispensing it to make sure the pills look normal.

Pfizer said in a statement that it is continuing monitor the situation and assess the need for further action.