With growing popularity of new weight loss drugs, doctors emphasize potential risks

When researchers learned that a class of drugs initially used to treat type 2 diabetes could also bring weight loss, the drugs Victoza and Ozempic gained popularity as a treatment option for obesity.

Given as daily or weekly injections, these drugs called GLP-1 RAs, help people produce insulin and lower the amount of sugar in the blood. First approved for use in type 2 diabetes patients in 2005 by the U.S. Food and Drug Administration, the medications were quickly noted to promote weight loss.

The FDA, in 2014, later approved a GLP-1 RA for chronic weight management. Additional drugs in the class have since been approved for weight loss.

Of the nearly 35 million Americans with type 2 diabetes, more than one in 10 were estimated to be taking these drugs in 2019, according to the Journal of the American Medical Association.

"I prescribe these medications 10 times per day," Dr. Amanda Velazquez, Director of Obesity Medicine at Cedars-Sinai Medical Center, told ABC News.

"Obesity is a chronic relapsing disease," Velazquez added and said that the weight loss effects of the medications wear off after drug discontinuation.

Novo Nordisk, the pharmaceutical company that makes Ozempic, Victoza and another drug called Wegovy -- which is specifically meant for weight loss -- said last December, "While we recognize that some healthcare providers may be prescribing Ozempic for patients whose goal is to lose weight, it is up to the clinical discretion of each healthcare provider to choose the best treatment approach for their patients."

Through the fall, there have been intermittent shortages of various dosages of Ozempic and Wegovy.

"There is high demand overall, more awareness of the medications because of their efficacy, and shortages in the supply chain with making the drug from manufacturers," Velazquez said.

Off-label use of the drugs may be contributing to this shortage.

"It is very frustrating for everyone," said Dr. Heather Sateia, Assistant Professor of Medicine at Johns Hopkins Hospital, told ABC News. "Pharmacies are so short-staffed that they won't let people know when it is back in stock so it is like a scavenger hunt- time-consuming and anxiety-provoking for patients."

A recent study from from the University of Montpellier published in Diabetes Care looked at type 2 diabetes patients who were treated with GLP-1 RAs from 2006-2018 and identified a link between the long-term use of these drugs and a higher likelihood of thyroid cancer. Specifically, the study found that people who took the drugs for one to three years were 58% more likely to develop thyroid cancer. Medullary thyroid cancer, a rare form of the disease, carried an even higher risk, according to the study.

"The newer findings provide interesting additional data to this clinical discussion, though are not independently enough to set a new standard for screening," Dr. Erik K. Alexander, Chief of the Thyroid Section in the Division of Endocrinology, Diabetes, and Hypertension at Brigham and Women's Hospital, told ABC News. "[These drugs] should only be used when the benefit of treatment outweighs known or suspected risk, and this assessment should be continually reconsidered by each patient with their physician on a regular basis."

45,000 Americans are diagnosed with thyroid cancer, but it is notably not a death sentence according to the American Cancer Society. With surgery and therapy, 5-year survival is 98% but this largely depends on the type of thyroid cancer and the stage of the disease. Medullary thyroid cancer has a relatively poor prognosis compared to the other types, according to the American Cancer Society.

In a statement, Novo Nordisk says extensive data from randomized trials, long-term studies, and real-world evidence "have not shown a causal relationship between use of GLP-1 receptor agonists and risk of thyroid tumors."

The company "remains confident in the benefit risk profile of its products and remains committed to ensuring patient safety," the statement said.

The drugs can sometimes cause nausea, injection site pain, and inflammation of the pancreas. Some patients taking concurrent diabetes medications can also experience low blood sugar levels.

Patients are currently monitored every 3-4 months with liver, diabetes, kidney, cholesterol, and electrolyte testing. Thyroid testing is currently not recommended.

"The data on thyroid cancer certainly gives me pause," said Sateia. "There is not currently a recommendation for thyroid ultrasound or serum calcitonin monitoring, but we are keeping an eye out for changes in those recommendations. I suspect we'll see a shift in this soon."

"This probably wouldn't change the way one prescribes but it is something to be aware of," Dr. Yufei Chen, Assistant Professor of General Surgery at Cedars-Sinai Medical Center, told ABC News.

Natalie S. Rosen, M.D., is a physician in the Hematology & Oncology Department at New York-Presbyterian Columbia and a former member of the ABC News Medical Unit.