Almost 200 cancer patients in New Brunswick are learning they were treated with watered-down chemotherapy drugs.

It’s an error that is affecting more than 1,000 Canadians, and 186 of them were treated at the Saint John Regional Hospital.

“To me, it just ups the ante. It just ups the stress level,” says cancer patient Dan Drost.

“All of a sudden, people which previously would never have thought ‘Am I sure I’m getting what I’m supposed to get?’ Now they’re going to question it.”

Dr. John Dornan, the hospital's chief of staff, estimates the affected patients received an average of 10 per cent less chemotherapy medication than they should have.

He also says it’s unclear what impact the lower-than-intended dose of cyclophosphamide would have on a patient’s chance of recovery.

“I don’t think it would, but we’re studying that to see if the dilution of a drug that we’ve given by anywhere between two and 20 per cent will have an impact on the disease.”

The hospital said in a statement that the affected drug was purchased from Marchese Hospital Solutions beginning in March 2012 and it is working with the supplier to determine the cause of the error.

Marchese Hospital Solutions said it is concerned by the questions raised about the quality of its work and it is addressing those issues.

"Our preliminary investigation of this issue leads us to be confident that we have met the quality specifications of the contract," the company said on its website.

Dr. Eshwar Kumar, the CEO of the New Brunswick Cancer Network, says the hospital stopped using the supply as soon as it learned of the problem last Thursday and is now mixing the drug themselves.

Moncton resident Lorna Savoy has struggled with bouts of breast cancer for 15 years. She is concerned about the impact on patients who have endured chemotherapy.

“In Saint John I understand they’ve been using that supplier for over a year, so to think of going through chemo and then to be told it was less than optimum, it would be just devastating,” she says.

At the provincial legislature in Fredericton, Premier David Alward said he was concerned after hearing about the diluted dosages.

"We feel for anyone who is dealing with cancer to start with, and then to get this news," Alward said.

The Saint John Regional Hospital has acquired a new supply of chemotherapy medication and is in the process of contacting affected patients.

On Tuesday, four Ontario hospitals announced they were contacting close to 1,000 cancer patients because of the same problem.

A total of 990 patients treated or being treated at the London Health Sciences Centre, the Windsor Regional Hospital, Lakeridge Health in Oshawa and Peterborough Regional Health Centre are affected.

Concerned patients are being asked to call their oncologist.

With files from CTV Atlantic's Mike Cameron and The Canadian Press