Canadian researchers have uncovered a possible hidden side effect of the popular weight loss drug. The drug began as a method of helping type 2 diabetes patients control their blood sugar. However, it’s being prescribed off-label as a method for people to lose weight and has grown extremely popular. The drug might be shrinking more than patients’ waistlines. Scientists at the University of Alberta have found that Ozempic and similar drugs shrink the human heart.

A pediatrics professor at UA named Jason Dyck was the lead author of the study. He serves in the Faculty of Medicine and Dentistry, and also on the Women and Children’s Health Research Institute. Professor Dyck notes that if people have been prescribed Ozempic because of type 2 diabetes, the benefits most likely outweigh the risks for them.

“However, the growing number of people who may be taking these drugs who do not meet the eligibility criteria and who are not at risk have a different risk-reward calculation that they should be made aware of,” he notes.

The team was attempting to discover why people taking Ozempic suffer a reported side effect of muscle loss. Semaglutide, known more popularly as Ozempic, was designed solely as a type 2 diabetes medication. All the drugs in the same class, however, are now being touted as an anti-obesity cure.

Professor Dyck’s team used obese and lean mice for their study. When they confirmed that Ozempic shrank the hearts of all the mice, they then confirmed the same findings with cultured human heart cells. While they did not notice any detrimental heart effects in the mice, Dyck cautions that this doesn’t mean it won’t impact humans. They may have more impacts from the drug over the long term that scientists haven’t discovered yet.

“Given the growing number of people taking this drug who have no cardiovascular disease or who are not classified as obese, we suggest that cardiac structure and function be carefully evaluated in previous and ongoing clinical studies,” says Dyck.

This research comes after another study that was published in The Lancet in November. An international team from the University of Alberta, McMaster, and Louisiana State University did a composite of studies into the effects of Ozempic from around the world. They found that up to 40% of the weight lost by Ozempic patients is actually muscle, rather than fat cells.

The researchers note that this loss of muscle is much faster than what people experience through the normal aging process or by reducing calories in their diets. Reduced muscle mass can lead to a number of long-term negative health effects, including a weakened immune system, slower wound healing, and an increased risk of infections.

“Muscle does much more than just help us move or lift things,” the study’s lead author notes. “It is a powerful organ that keeps us healthy in a number of ways.”

The researchers suggest increasing protein intake while taking weight-loss drugs and doing plenty of resistance training such as lifting weights to maintain muscle mass. It’s unclear whether that will work with patients taking Ozempic, however, since the drug works to mask their appetite.

An estimated 15 million Americans are now taking prescription Ozempic for weight loss and most are not type 2 diabetics. The fastest-growing age group that is taking the drug is women and girls between the ages of 12 and 25. The drug is being so over-prescribed for non-diabetics that the Food and Drug Administration has announced shortages of Ozempic in the past year.