U.S. presidential hopeful Bernie Sanders travelled to Canada Sunday with a group of Americans living with diabetes, purchasing insulin at a Windsor, Ont., pharmacy for far less than across the border.

In the U.S. the cost of a vial of insulin is about $340 ($450 Cdn). In Canada, the same vial will average about $30. On Sunday, an "insulin caravan" rolled through the border city of Windsor, carrying about 15 people with Type 1 diabetes.

According to Sanders, the massive price difference is a result of "pharma's greed."

"Over the last 20 years, the pharmaceutical industry has spent hundreds of millions of dollars of campaign contributions. They buy and sell politicians — Republicans and Democrats," Sanders told a crowd of supporters outside the pharmacy.

"They continue to charge the American people any price they want."

I just boarded the bus in Detroit with diabetics, on our way to Windsor, Canada, to buy affordable insulin.<br><br>Americans are paying $300 for insulin. In Canada they can purchase it for $30. We are going to end pharma’s greed. <a href="https://t.co/PuR520Y7Qy">pic.twitter.com/PuR520Y7Qy</a> —@BernieSanders

One of the travellers was Hunter Sego, who has had Type 1 diabetes for 16 years since he was seven. Through tears, his mother, Kathy Sego, told the crowd about her family's struggle to afford a specific type of insulin.

She said Hunter felt like a burden to the family because he needed four or five vials of NovoLog insulin a month, which costs about $1,500.

"My son decided he would take it upon himself to ration his insulin," she said. "It was pretty scary as a mom to know that your son felt that he was a burden to you."

Hunter explained the effects of rationing his insulin, including muscle decay and energy shortages.

"This should not be going on in America," said Sanders.

Also in the caravan was Sahil Mehta, who said his father "does a lot of business in India" and would bring insulin from there to the U.S. for him.

"He can get four times the amount there," said Mehta.

WATCH: A family is telling their story of having to ration insulin because of high prices in the U.S. <a href="https://t.co/nCi5zlavmp">pic.twitter.com/nCi5zlavmp</a> —@sanJmaru

Outside the pharmacy, about 30 supporters of the Vermont senator gathered outside the Olde Walkerville Pharmacy in Windsor. One of them was eight-year-old Clara Whited from Windsor, who has Type 1 diabetes.

Her mother, Rebecca, said she has family in the U.S. and could not fathom being unable to afford a life-saving drug for her daughter.

"When I see headlines of people passing away because they're having to ration their insulin and they can't afford it [and] when you live with someone with Type 1, I can't imagine," she said.

"What if it was your mother? Your brother? Any family member? I would give anything I could to afford the insulin to buy it — but we shouldn't need to do that."

Eight-year-old Clara Whited of Windsor has Type 1 diabetes. Her parents say it's 'devastating' that children in the U.S. are dying because life-saving medicine is too costly. (Sanjay Maru/CBC)

"This is not a new thing. This has been happening here in Canada all the time, especially the pharmacies closer to the border," said John George, operations manager of the pharmacy

"We feel bad for them. But we do our best. Our pricing here is a lot more moderate."

In a letter this week, 15 groups representing patients, health professionals, hospitals, and pharmacists warned Health Minister Ginette Petitpas Taylor of the potential for drug shortages in Canada from Americans coming across the border.

"The Canadian medicine supply is not sufficient to support both Canadian and U.S. consumers," the letter reads. "The supply simply does not, and will not, exist within Canada to meet such demands."

Americans are allowed to take 90 days worth of insulin across the border at a time, according to Diabetes Canada.

A reporter asked Sanders if he was concerned that Canada will see a drug shortage for this reason.

"I don't believe that is the case," he said immediately before leaving Windsor.