From sagging jowls and sulfurous burps to deflated breasts and surprise pregnancies, the side effects of GLP-1 weight-loss drugs have ranged from subtle to strange.
Now, new research suggests that these wildly popular medications may also be throwing off critical medical imaging scans, interfering with doctors’ ability to detect serious — even deadly — diseases.
Experts say this could lead to delayed diagnoses and treatments for some patients, while others might undergo tests and procedures they didn’t need in the first place.
Originally developed to treat Type 2 diabetes, GLP-1 meds have become a sensation due to their powerful weight-loss effects. In the US alone, usage jumped a staggering 700% between 2019 and 2023.
These drugs mimic a natural hormone called GLP-1, which helps regulate blood sugar and appetite. They also boost insulin production, slow digestion and make people feel full longer, helping them slim down in record time.
While these biological changes can improve health, they may interfere with PET-CT scans, a tool doctors use to detect cancer and inflammatory diseases.
The science behind the scare
PET-CT scans combine two powerful imaging tools to give doctors a detailed picture of what’s happening in the body.
The PET scan uses a radioactive substance called FDG that travels through the bloodstream and is absorbed by tissues. Cancer cells and other abnormal cells — like those involved in inflammation — soak up more FDG because they have a higher metabolic rate, according to UConn Health.
The PET scanner detects the radiation emitted by the FDG, creating images that highlight where the substance has collected.
The CT scan, meanwhile, provides detailed pictures of organs, bones and tissues.
When combined, PET-CT scans reveal the body’s metabolic activity and its physical anatomy, helping doctors make diagnoses and track how patients respond to treatment.
But in patients taking GLP-1s, doctors have observed unusual patterns of FDG — i.e, hot spots in the body that can mask signs of cancer or make healthy tissue look diseased.
“We noticed unusual uptake in one of our patients on a GLP-1 agonist, which prompted a wider review across our network,” Dr. Peter Strouhal, medical director at Alliance Medical Ltd in the UK and lead author of the new study, said in a statement.
“We found that these altered patterns are increasingly common, yet there is currently no national or international guidance in the UK addressing this emerging issue,” he noted.
Confusing scans, costly consequences
In the US, about 1 in 8 adults report having used a GLP-1 medication like Ozempic, Wegovy or Mounjaro, according to a 2024 survey by the Kaiser Family Foundation.
With demand showing no signs of slowing, more patients are likely to display these unusual patterns on their PET-CT scans.
That’s especially concerning because cancer rates in the US are rising — particularly among young adults — and early detection is crucial for successful treatment.
Doctors warn that misreading these FDG uptake patterns can lead to unnecessary tests, incorrect cancer staging and dangerous delays in care.
“Recognizing the characteristic uptake associated with GLP-1 agonists helps avoid unnecessary anxiety and interventions, ensuring patients receive the right care, at the right time, without detours or doubt,” Strouhal said.
For now, Strouhal and his colleagues don’t recommend patients stop taking GLP-1 medications before undergoing PET-CT scans.
Instead, they suggest imaging teams carefully document their patients’ medication histories to help doctors interpret their scans while formal guidelines are being developed.
Their research was presented Tuesday at the 38th Annual Congress of the European Association of Nuclear Medicine.
Looking ahead, the team plans to expand its data collection across more imaging centers to build stronger evidence for future national guidelines.
They also aim to collaborate internationally, so patients worldwide can benefit from consistent, reliable PET-CT interpretations.
