When Hunter Sego realized the insulin he needed to manage his type 1 diabetes cost more than $1,400, he called his mother in a panic. His family had insurance. He did not believe it was possible a one-month supply of “life-saving” medication could cost so much.

The price tag was correct.

Sego, then a student and football player at DePauw University, began to ration his insulin, using a quarter of what had been prescribed. He lost weight. His grades dropped. He struggled on the field.

Fortunately, his mother found out and stopped him from limiting his insulin intake – a practice that is increasingly common and potentially deadly.

On Sunday, Sego and his mother, Kathy, drove seven hours from Indiana to join a caravan of roughly a dozen patients with type 1 diabetes on a bus to Canada with Bernie Sanders. The Americans – wearing glucose monitors on their arms and shirts that said “diabetic” – set out to buy insulin for a fraction of its cost at home.

Sanders’ northern sojourn, a trip his campaign sponsored, was designed to highlight the rising cost of prescription drugs in the US, which the senator said was the result of “incredible corruption and greed” on the part of the US pharmaceutical industry.

“How does it happen 10 minutes away from the American border in Michigan, people here are paying one-10th of the price for the vitally important drug they need to stay alive?” Sanders asked, calling the disparity a “national embarrassment”.

In his remarks outside of the Olde Walkerville Pharmacy in Windsor, Sanders vowed that as president he would appoint an attorney general to investigate the pharmaceutical industry for what he described as “collusion” between the major drug companies.

“Prices go up and up and up at the same level for the same companies,” he said. “So what you do is you throw these people in jail if they engage in price-fixing.”

The greed of the pharmaceutical industry – the corruption of the pharmaceutical industry – is scandalous Bernie Sanders

The trip came just two days before the second Democratic debate in Detroit. Among 20 candidates over two nights, healthcare is expected to be a major flashpoint.

Sanders has exchanged barbs with former Vice-President Joe Biden, who has called the senator’s healthcare policies “risky”. Sanders has accused Biden, whose healthcare plan would build on the Affordable Care Act, of not being honest about Medicare for all.

Sanders’ signature proposal, which would give the US something similar to Canada’s national healthcare system, has framed the party debate. Several leading candidates support some version of it.

The bus took about an hour to drive six miles across the Detroit river to Windsor, Ontario. Sanders listened as people told their stories.

Quinn Nystrom, a type 1 diabetic who organizes caravans out of Minnesota, said she knew people who had lost limbs, been hospitalized or even died as a result of rationing medicine.

“Insulin is our oxygen,” she said, stressing that caravan trips are not a sustainable solution to the problem, especially because many cannot afford to take a day off of work or find the fee to apply for a passport.

“What [the pharmaceutical companies] are doing to Americans is price-gouging us and they’re holding us hostage and people are dying,” she said.

When the bus arrived at the pharmacy, around 100 Canadians greeted the passengers. Some held signs that said “Insulin is a human right”. A little girl held a Sanders plush toy with a button on the back that said: “Push to activate the revolution.” An elderly man played accordion while trying to finagle a moment with the senator.

In Canada, insulin does not require a prescription. When the American group finished their purchases, Sanders drew gasps from the Canadian crowd.

Sanders talks with type 1 diabetes advocate Quinn Nystrom as they ride the bus across the border. Photograph: Rebecca Cook/Reuters

Citing a Yale study, he told them that one in four American diabetics ration their insulin because of cost. That prince for one vial has risen astronomically in two decades, he said, as pharmaceutical companies have spent “hundreds of millions of dollars on campaign contributions” and “billions of dollars lobbying Congress”.

“Shame!” someone shouted.

Another yelled: “Disgrace!”

“They buy and sell politicians, Republicans and Democrats,” the senator said, “to make sure that they can continue to charge the American people any price they want. This is not just insulin, it is prescription drug after prescription drug.”

Kathy and Hunter Sego paid $1,000 for 25 vials of insulin, enough for about six months. They estimated it would have cost $10,000 more for the same supply back home.

Speaking to the crowd at the pharmacy, she described the hardship of choosing to pay the electricity bill or for son’s medicine. On at least two occasion’s their power has been turned off.

“How can that be that in the United States of America that I am paying so much for insulin?” she asked, fighting back tears.

Pharmaceutical companies are price-gouging us and they’re holding us hostage and people are dying Quinn Nystrom

Sanders’ Medicare for All plan would cap the out-of-pocket costs for prescription drugs at $200 per year. Earlier this year, he introduced a package of bills aimed at lowering prices. The legislation would allow the government to directly negotiate with drug manufacturers, to obtain lower prices for Medicare beneficiaries. It would also enable US consumers to import pills from Canada and other industrialized countries and it would set drug prices based on what they cost in those other places.

“This resonates in Canada as well,” said Nada Temerinski, 29, who had come from Montreal.

Unlike Sanders’ vision for the US, Canada has a private heath insurance since its system does not cover the cost of all benefits, such as prescription drugs. Instead, a review board negotiates prices in part based on rates in other countries.

“I would hope that it inspires Canadian politicians,” Temerinski said of Sanders’ work. “I’m hoping as America moves further left, that Canada does as well and ideally we could move towards prescription-free.”

Rachael Lockwood, of Grand Rapids, Michigan, was sharing insulin prescribed for one child with type 1 diabetes between two when another son was diagnosed.

“We were desperate,” she said. On Sunday, she and her three children aged seven, 12, and 16, made their second trip to Canada for the insulin.

In 2016, she voted for Donald Trump in hopes that a businessman might be able to fix the nation’s problems. But now that she is a “medical refugee,” as one member of the caravan described them, forced to travel abroad for affordable medicine, her perspective has changed. Trump, she said, will not be her choice in 2020.

This was not Sanders’ first trip to Canada for prescription drugs. He said he had made a similar trip from Vermont to Montreal, with women with breast cancer.

“It never ends,” he said, shaking his head. “The greed of the pharmaceutical industry – the corruption of the pharmaceutical industry – is scandalous and we have got to take them on.”