“You’d be crazy not to give it a try and learn more about what it can do,” Dr. Krumholz said.

Microsoft wanted to know that, too, and with OpenAI, gave some academic doctors, including Dr. Kohane, early access to GPT-4, the updated version that was released in March, with a monthly fee.

Dr. Kohane said he approached generative A.I. as a skeptic. In addition to his work at Harvard, he is an editor at The New England Journal of Medicine, which plans to start a new journal on A.I. in medicine next year.

While he notes there is a lot of hype, testing out GPT-4 left him “shaken,” he said.

For example, Dr. Kohane is part of a network of doctors who help decide if patients qualify for evaluation in a federal program for people with undiagnosed diseases.

It’s time-consuming to read the letters of referral and medical histories and then decide whether to grant acceptance to a patient. But when he shared that information with ChatGPT, it “was able to decide, with accuracy, within minutes, what it took doctors a month to do,” Dr. Kohane said.

Dr. Richard Stern, a rheumatologist in private practice in Dallas, said GPT-4 had become his constant companion, making the time he spends with patients more productive. It writes kind responses to his patients’ emails, provides compassionate replies for his staff members to use when answering questions from patients who call the office and takes over onerous paperwork.

He recently asked the program to write a letter of appeal to an insurer. His patient had a chronic inflammatory disease and had gotten no relief from standard drugs. Dr. Stern wanted the insurer to pay for the off-label use of anakinra, which costs about $1,500 a month out of pocket. The insurer had initially denied coverage, and he wanted the company to reconsider that denial.

It was the sort of letter that would take a few hours of Dr. Stern’s time but took ChatGPT just minutes to produce.

After receiving the bot’s letter, the insurer granted the request.

“It’s like a new world,” Dr. Stern said.