Police in Trois-Rivières, Que. say they have opened a criminal investigation after receiving a complaint that a daycare worker allegedly gave children melatonin without their parents' consent.

Police spokesperson Luc Mongrain confirmed the investigation was started on May 17 and that investigators are set to speak with parents and daycare staff to see whether they will refer the case to prosecutors.

The incident happened at La Garderie Sportive des P'tits Samouraïs in Trois-Rivières, a city between Montreal and Quebec City.

Melatonin is a natural hormone produced by the brain, particularly during the evening, to induce sleep, Dr. Alain Vadeboncoeur explained in an interview with Noovo Info.

The natural or synthetic product is widely available locally in pharmacies and health food stores.

Vadeboncoeur, an emergency room physician and former head of the ER at the Montreal Heart Institute, said while it is a relatively mild product, there can be side effects and it probably shouldn't be the first choice to regulate sleep.

When it comes to children, there are certain medical conditions for which melatonin is an option. But the fact that a child is "rambunctious" or "refuses to go to sleep" is not a reason to administer it, he said.

"It's not a daytime medication either. It's for sleeping at night basically," Vadeboncoeur said.

Last February, The Associated Press reported that an ex-daycare director in Indianapolis was charged after being accused of giving children melatonin gummies without parental consent to get them to sleep. In that case, the former director and a current employee allegedly gave the gummies to 17 kids between the ages of one and four

Several parents told local police their children had problems, including trouble sleeping and developing a rash.

With files from Noovo Info