Corrections & Clarifications: This story has been updated to reflect royalty payments for a 1923 patent.

Meaghan Carter died alone on the sofa of her suburban Dayton, Ohio, apartment last Christmas.

Like most people with Type 1 diabetes, the 47-year-old nurse had a kit of essential supplies within reach. It contained two empty vials of her preferred insulin, a partial vial of inexpensive Walmart insulin and a half-filled container of testing strips to measure blood glucose levels.

Uninsured, between jobs and with $50 in a bank account, Carter probably had attempted to stretch a limited supply of insulin until she got a final paycheck from her last job, family members say. She was scheduled to begin a new nursing job the following week that offered health insurance.

“There was no insulin at all in the refrigerator,” says Mindi Patterson, Carter’s sister-in-law. “She had gauze, bandages and all her nursing supplies. She had plenty to take care of others but not enough to take care of herself.”

The cost of insulin for diabetics such as Carter has drawn national scrutiny as Congress examines factors contributing to the nation’s escalating prescription drug prices. All people with Type 1 and some with Type 2 diabetes need the drug, but regular price hikes make insulin difficult to afford for the uninsured and those whose coverage requires significant cost sharing.

Patient advocates are becoming increasingly vocal about the affordability of a drug invented nearly a century ago by scientists who took steps to make the medicine inexpensive. One group staged protests outside the offices of the nation's three dominant insulin makers.

Canadian scientists discovered insulin in 1921, treated the first diabetic patient in 1922 and sold the patent to the University of Toronto for 3 Canadian dollars. The university administered the patent and received royalty payments from drug companies that sold human insulin.

The price of modern versions of a drug that more than 7 million Americans need to live nearly tripled from 2002 to 2013, according to one study. Type 1 diabetics paid an average of $5,705 for insulin in 2016 – nearly double what they paid in 2012, according to the Health Care Cost Institute.

Diedre Waxman lives in Newton, Mass., and has Type 1 diabetes. Diagnosed six years ago, Waxman has adopted a strict diet, so she doesn’t need as much insulin, which she purchases from Canada. Erin Clark for USA TODAY

Patient advocates say people have resorted to extreme measures such as taking less than the doctor prescribed to make it last longer, acquiring the drug from friends or getting it from less expensive pharmacies in Canada or Mexico.

More: Lack of insulin could affect 40 million people with diabetes by 2030, study finds

Last month, the powerful Senate Finance Committee asked the three dominant insulin makers detailed questions about the drugs' price increases. The price for one vial of Eli Lilly's Humalog surged from $35 in 2001 to $234 in 2015. From 2013 to this year, Novo Nordisk's Novolog jumped from $289 to $540 and Sanofi’s Lantus from $244 to $431, according to a committee letter.

A vial of insulin loses potency after being opened for 28 days. The amount of insulin a patient needs varies depending on such factors as age, weight, diet and overall health.

Among things senators want to know: How do drugmakers set insulin prices, and what’s the role of rebates and discounts to middlemen pharmacy benefit managers?

Senators are not limiting questions to Big Pharma. The nation's largest pharmacy benefit managers, who drew scrutiny for their increasingly powerful role as middlemen in the drug supply chain, will appear before the committee April 3.

Drugmakers say they've taken steps to address prices, offered co-pay cards to limit out-of-pocket expenses and funded patient-assistance programs that provide free medication to thousands of vulnerable Americans.

Sanofi pledged to limit annual price increases to less than the average health spending rate.

This month, Eli Lilly unveiled a half-price version of Humalog called insulin lispro for $137.50 for a single vial. It's the same drug as Humalog, only with a different label.

In a statement, Eli Lilly CEO David Ricks said the lower-cost insulin is a "bridge that addresses gaps in the system until a more sustainable model is achieved."

Simeon Taylor, a University of Maryland School of Medicine diabetes researcher, says Type 1 diabetics without adequate insurance coverage are vulnerable to price increases because they can't live without the drug.

"Insulin is not an optional medication,” says Taylor, who formerly worked for Eli Lilly and the National Institutes of Health. “People have to buy insulin no matter what the cost is. That gives a lot of strength to the people selling insulin.”

'Whole system needs to be evaluated'

Some suggest that a simple across-the-board price cut might not work for all patients under the system.

The American Diabetes Association convened an Insulin Access and Affordability Working Group to study rising insulin prices and affordability of the life-sustaining medicine. The group's study concluded that a complex supply chain from the drug factory to the pharmacy might promote higher prices.

Pharmacy benefit managers, which negotiate drug prices on behalf of health insurers, demand rebates from drug manufacturers. Their leverage: placing the drug on an insurer’s formulary – the list of drugs that the insurance company will cover for insured consumers.

A drugmaker that offers a lower rebate might be excluded from a prescription drug plan or be placed on a less favorable tier that requires consumers to pay a larger portion on the tab.

More: Insulin costs nearly doubled from 2012 to 2016, report says

The ADA's working group's report found that even though drugmakers' "list prices" for insulin have surged, their "net prices" have grown at a more modest rate. The list price is how much the drugmaker charges. The net price is money the drugmaker gets after fees, discounts and rebates to wholesalers or pharmacy benefit managers.

Consumers are not privy to these behind-the-scenes negotiations between pharmacy benefit managers and drug manufacturers. All of this is done outside the public’s view.

“A lot of attention has focused on the manufacturers and less on the other players in the supply chain," says Karen Van Nuys, a research professor at USC’s Schaeffer Center for Health Policy and Economics and member of the ADA's working group. "We think those players also share responsibility for what happens to prices and access.”

Van Nuys says that if one drugmaker lowers insulin prices, that could put it at a competitive disadvantage compared with peers. That is because pharmacy benefit managers might still require a significant rebate.

Novo Nordisk says its insulin net prices declined at double-digit rates in 2017 and 2018 because of rebate demands.

"The whole system needs to be evaluated,” Van Nuys says.

Study: Cost affects insulin use

Newton, Massachusetts, resident Deidre Waxman has good prescription-drug coverage through Medicare.

But she worries that the $1,300 to $1,500 monthly retail cost of her insulin will be unaffordable if she reaches the doughnut hole, Medicare's deductible that kicks in once drug spending exceeds $3,820.

She does not fill insulin prescriptions at her neighborhood pharmacy; she gets her medicine from Canada. Her husband buys insulin during his frequent work trips there, and she will take a six-hour car trip to Canada once a year to get insulin. A third source is Mark's Marine, a Vancouver, British Columbia, pharmacy that ships to U.S. patients.

Waxman does not need much insulin because she is on a low-carbohydrate diet. If she has excess insulin, she packs it in styrofoam containers cooled with ice packs and sends it to fellow diabetes patients who can't afford the drug.

"I send it to friends who are in dire need," Waxman says. "These are people who would die without insulin."

Diedre Waxman's diabetes bag includes the pen she loads with cartridges to administer her insulin. Erin Clark for USA TODAY

For those without robust insurance coverage, there are signs they are having difficulty affording insulin.

Kasia Lipska is an endocrinologist at Yale School of Medicine. Lipska noticed that more Yale Diabetes Center patients seemed to struggle to pay for insulin, so doctors surveyed patients about whether cost influenced their insulin use.

One in four patients responded that cost prompted them to use less insulin than prescribed, take smaller doses, stretch out supplies, not fill a prescription or not start the drug. It was a small study at one center in Connecticut, and researchers can’t be certain whether insulin affordability is better or worse in other states.

People who struggle to pay are “more in the middle,” Lipska says. They don’t qualify for Medicaid, the state insurance plan for low-income residents, and some earn too much to qualify for patient-assistance programs.

A person with Type 1 diabetes who discontinues the drug might get sick, hospitalized with diabetic ketoacidosis or die, she says.

More: Eli Lilly to introduce generic version of insulin drug Humalog that cuts price in half

The health problems of diabetics who take less than they need might take longer to detect but can be just as serious.

Taking less insulin than prescribed can lead to serious health harms, Lipska says. Those could include a diabetic ulcer, a foot infection that leads to amputation or kidney damage.

“We know it’s a problem,” Lipska says. “The problem leads to, in very severe cases, patients dying, people having complications, people being admitted to the hospital.”

'You realize you don't have any left'

Blind in one eye and her vision rapidly deteriorating in the other, Sarah Theubet could not afford the medicine her body needed to slow the harmful effects of diabetes.

Insulin was too expensive. The uninsured Redding, California, resident could not afford the cost of a drug that had more than tripled since the early 2000s.

"It was terrifying," Theubet says. "You are looking at the vial, and you realize you don't have any left."

Theubet turned to friends she met through social media in 2016 and 2017 to solicit insulin donations while she drastically changed her diet so she would not need as much medicine.

She ate one low-carbohydrate meal each day that rarely varied: sliced lunch meat and cheese, no bread.

She barely had enough energy to make it through classes at Shasta Community College. Vision in her right eye, stabilized this decade from an operation, began to worsen because she could not afford to take insulin as prescribed. She is blind in her left eye.

"With the rationing, that was the first year my ophthalmologist noticed a (vision) decline because I was all over the place," Theubet says of her insulin use.

More: Soaring insulin prices prompt insurance shift

Sarah Theubet, 38, has Type 1 diabetes that robbed her of her vision in one eye and will eventually render her blind. Michael Chapman, Redding Record Searchlight via USA TODAY NETWORK

Because she is legally blind, she qualified for Social Security disability in 2017, which includes health insurance through Medicare. She now gets the insulin she needs.

Now that her health coverage and access to insulin are stable, she has thrived in the classroom. She will complete her general education studies in the fall and plans to transfer to the University of California-Davis to complete her communication degree.

She wants to advocate for the disabled.

"I am doing the best I can with what I've been given," Theubet says.

'Symptom of dysfunctional' system

Some say government needs to step in because the private sector has failed to check price increases.

Taylor, a member of the ADA working group, says insulin pricing is emblematic of the nation's health system flaws.

Pharmacy benefit managers started to counter pharmaceutical industry's pricing power. As these middlemen gained more clout, they began to demand higher rebates. Drug companies raised prices by amounts that are slightly less than what pharmacy benefit managers demanded.

"This is a symptom of a dysfunctional health care system in the United States," Taylor says. "I don't want to put all the blame on the companies. From my point of view, the responsibility is in how our health care system is designed."

More: Big Pharma CEOs tell senators they won't reduce drug costs without other changes

Carter, the Dayton-area resident, was hospitalized twice for complications this decade and struggled to afford insulin months before she died, Patterson says.

She spent $25 to buy Novolin NPH insulin from Walmart on Dec. 20, according to a receipt the family retrieved from her apartment after her death. Novolin is an older version of human insulin that must be adjusted based on regular blood and glucose testing.

"I told her it was pretty unpredictable," Patterson says of Novolin. "You only use it if you have no other option."

Carter was struggling on Christmas Day, feeling nauseous and slurring her words, a roommate told Huber Heights police.

The roommate told police she thought Carter's blood-sugar levels were off and urged her to call a doctor or a paramedic.

Carter refused, and the roommate left for work. When the roommate returned from work that night, she noticed Carter appeared to be sleeping on the sofa. The following morning, the roommate checked on Carter and realized she had died.

The Montgomery County Coroner determined Carter died on Christmas night, but the agency did not consider the death suspicious and did not perform an autopsy. Carter often did not take her insulin as directed, the roommate told police.

A family doctor signed her death certificate, listing the cause of death as cardiopulmonary arrest.

Patterson, whose husband and two sons have Type 1 diabetes, is convinced her sister-in-law experienced a type of complication called diabetic ketoacidosis before she died.

She says she desperately wants to see a reformed system so patients can afford the medication they need to live.

"The system is broken," Patterson says. "Let's start with transparency, so we can see exactly where it's broken. Then we can see where to fix it."