Health Canada is urging people who bought a specific herbal product that's promoted as a sleep aid to return it to the store where it was purchased.

The product, called Eden Herbal Formulations Serenity Pills II, contains the undeclared drug estazolam, which can be habit-forming when used for a few months, an advisory says.

Users should talk to a health-care professional before they quit taking it because there's a risk of withdrawal symptoms. The product isn't authorized for sale in Canada.

Estazolam belongs in the class of drugs known as benzodiazepines, which should only be prescribed by a doctor. It should not be used by people with an allergy to any benzodiazepines, such as Valium (diazepam), Restoril (temazepam) and Ativan (lorazepam), or by people with sleep apnea or the neuromuscular disorder myasthenia gravis.

Side-effects can include dizziness, drowsiness, confusion, depression, loss of memory and hallucinations. Eden Herbal Formulations Serenity Pills II were distributed by the Evergreen Acupuncture Clinic in Calgary. The clinic has stopped selling it, but people may still have the pills in their medicine cabinets.

No adverse reactions connected to the pills have been reported in Canada.

It's the fourth warning in recent months related to estazolam. Previously, Health Canada said the undeclared drug was found in Salt Spring Herbals Sleep Well Dietary Supplement, Sleepees and Eden Herbal Formulations Sleep Ease Dietary Supplement.