When his chemotherapy patients leave the hospital to continue treatment at home, Edward Greeno faces a new challenge.

He can no longer ensure they're taking their medicine.

Greeno, the medical director of the Masonic Cancer Clinic at America's University of Minnesota, has come to realise that some patients, like children hiding naughty behaviour from a parent, will fudge the truth to avoid his disapproval, even when their health is at risk.

To combat patients' fibbing and forgetfulness, Greeno has recently begun using a new tool: A pill embedded with a tiny, ingestible sensor. The sensor transmits data from inside the patient's body to a wearable patch on their abdomen, which links to a mobile app that patients and doctors can access. That data offers a new window into patients' health and behaviour, Greeno said, allowing doctors to remotely monitor someone's heart rate, activity level and sleep cycle. The sensor, which is about the size of a grain of sand and dissolves in the gastrointestinal tract, also tells doctors when a patient has ingested their medication. The information is compiled in a database that doctors can access from their devices.

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At the Masonic clinic, as part of a pilot programme, doctors have begun pairing the sensor - made by California company Proteus Digital Health - with a common chemotherapy drug used to treat stage three and four colorectal cancer patients.

"You'd think for cancer treatment that patients would be pretty diligent, and that's not always the case, for a variety of reasons," he said.

Ingestible technology has raised a variety of concerns among experts and ethicists since the Food and Drug Administration approved digital pills in 2017, from how physicians will use the new data created by the technology to whether that data may be vulnerable to hackers.

"The health industry is behind the curve when it comes to cybersecurity," says Jason Christopher, chief technology officer at the cybersecurity company Axio. "Forget health record databases - how do you patch a digital pill?"

Despite the concerns, many experts have pointed out that the technology will help doctors ensure patients are taking their prescribed medication. Not taking medicine - or "medication nonadherence" in the health-care world - is a "common and costly problem," according to a study cited by the National Centre for Biotechnology Information.

It says 30 to 50 per cent of US adults don't stick to long-term medications, leading to about US$100 billion ($148.2b) in preventable costs annually.

Comparing medication nonadherence to weight loss, NCBI researchers say the problem is more complex than it might seem and often has multiple complicating factors. Greeno agreed, pointing out his patients aren't always lying about their behaviour. Sometimes older patients have trouble opening pill bottles. Other times, he said, they're so tired and foggy they struggle to stick to a rigorous schedule that requires them to take many pills each day. And sometimes they struggle to deal with side effects.

The problem is that chemo drugs can have a very narrow therapeutic window and often cost between US$10,000 and $20,000 a month.

"I had one patient whose hands hurt and she couldn't open her pill bottle," Greeno said. When her daughter was around she would take her pills, but when her daughter was gone, she wouldn't.

"Normally, I might not find out about until weeks later ... Now, the app is telling me in real time that she didn't take her pills and I get that message in clinic the next morning."

Brenda Jans Darling, 45, is a working mother of two juggling recovery with a daily onslaught of activities.

The sixth-grade maths teacher in Minnesota said she initially agreed to do a digital medicine pilot programme about three months ago because she thought it sounded interesting. She quickly found she enjoyed seeing health data like her sleep and activity levels tracked on an app. She found that information useful, comparing it to a "medical Fitbit".

But what she finds most useful is knowing she no longer needs to count her medication to ensure she hasn't missed a dose at the end of a busy two-week cycle.

Now when she forgets she gets an alert on her iPhone that says, "We have not received data from your 8am dose."

Darling isn't worried about her doctors having access to an ever-growing amount of personal health information and believes that data will be used to combat the disease she's spent the past two years battling. "I'm going to do whatever I can to advance cancer research so we can find a cure to our modern-day plague."