Parents of young children may need a prescription for over-the-counter fever and pain medication due to a shortage at some pharmacies, Toronto's Hospital for Sick Children is warning.

In a letter sent to caregivers, the hospital said some pharmacies across the country are dealing with supply shortages of liquid Tylenol and Advil.

"If your child requires the liquid form of acetaminophen, you will now require a prescription," the letter says. "It cannot currently be sold over the counter because it has to be repackaged from large bottles into smaller bottles by the pharmacist."

In a statement to CTV News Toronto, a SickKids spokesperson said that pharmacies such as Shoppers Drug Mart, in addition to SickKids' inpatient pharmacy, are impacted by the nationwide shortage. The hospital says that children staying overnight at SickKids will be able to get the medication, but those who visit the hospital and then go home will need to get a prescription from their health-care provider.

“While some retail pharmacies may have adequate supply of these over-the-counter medications, other pharmacies may only have them available in large quantities that must be dispensed by a pharmacist. For this reason, the medication may require a prescription,” Sarah Warr, senior communications advisor for SickKids, said.

"The health and safety of our patients is our top priority and we continue to closely monitor this situation," Warr said. "We have been working with our vendors and clinical partners to develop and implement strategies to help preserve our remaining supply."

Jen Belcher, vice president of strategic initiatives and member relations for the Ontario Pharmacists Association, says this recommendation doesn't mean customers can’t buy liquid Advil and Tylenol over the counter.

“The prescription does make it easier in the sense that it provides instructions for dispensing of that product. But ultimately, liquid Tylenol has not changed from an over the counter drug to a prescription-only product,” she told CP24.

Belcher explained that the shortage is impacting smaller bottles that are normally sold over the counter, which is why they are recommending parents get prescriptions in some cases so that pharmacists can use larger stock bottles to fill those requests.

SickKids also recommends that parents consider other forms of medication, including chewable tablets.

"Speak to your pharmacist or health-care provider first to ensure you give your child the right dose," the letter adds.

The shortage comes a month after the Ontario Pharmacists Association warned that heightened demand and supply chain constraints were fueling a shortage of cold and flu medication.

"If you go to pharmacies across Ontario and other provinces, you're likely to see a number of different gaps on our shelf," Belcher told CTV's Your Morning in July.

"(The medication) could be back by fall when we return to regular cold and flu season but it's really hard to predict at this point in time and I couldn't say with any degree of confidence, unfortunately."

At the time, Belcher said some children's painkillers were on backorder.

CTV News Toronto has reached out to the Ministry of Health as well as Shoppers Drug Mart for more information on how the shortage is impacting Ontarians.

It is unclear how many pharmacies are affected.