TORONTO (Canadian Press) -- Consumers should avoid taking a daily dose of the antidepressant Celexa in excess of 40 milligrams, as higher doses can cause abnormal heart rhythms, the drug's Canadian distributor says.

Lundbeck Canada said Monday that a research study found that doses of Celexa (citalopram hydrobromide) above 40 mg can affect electrical activity of the heart.

Celexa is used to treat depression and is available as 20-mg and 40-mg tablets, with 20 mg per day the maximum recommended dose for patients who are 65 or older, have liver problems, or take the heartburn treatment cimetidine at the same time.

Celexa should not be taken by consumers with the heart condition known as congenital long QT syndrome or if they have known QT interval prolongation, which is a change in the electrical conductivity of the heart.

High doses of Celexa can cause changes to the electrical activity of the heart that can lead to life-threatening abnormal heart rhythms.

Anyone taking Celexa or a generic version of the drug who experiences symptoms of abnormal heart rhythms, such as heart palpitations, dizziness, fainting or seizures, should contact their health-care professional immediately, Health Canada said.

Before starting treatment with Celexa, patients should inform their doctor of any heart problems, other medications being taken and whether they have had low blood levels of potassium and-or magnesium.

Those already taking the medication should consult with their doctor to ensure they are taking the correct dose. The doctor also should be consulted before stopping or reducing the dosage.

(c) The Canadian Press, 2012