Ozempic and Mounjaro masked our cancer symptoms — even doctors were unconcerned

Welcome to The Thin Line, The New York Post’s series about the darker side of GLP-1 drugs. Though GLP-1 agonists sold under brand names like Ozempic have helped millions of people lose weight, manage diabetes and improve other health conditions, they are not without risks. Check back for more stories about the lesser-known downsides of these wildly popular medications.

Brooke Hinderhan thought she had turned a corner with her health.

After metformin failed to control her diabetes, doctors prescribed Ozempic. For a time, the popular GLP-1 drug worked, bringing her blood sugar under control.

Even the side effects were manageable — until she developed severe fatigue, followed by diarrhea and stomach cramps that left her doubled over in pain.

“I thought it was just the Ozempic,” said Hinderhan, 47, a registered nurse case manager from Norris, Illinois.

The reality, she would later learn, was far more serious: Cancer had been growing in her colon, and what she assumed were routine side effects were actually early warning signs of the disease already taking hold.

Her experience is part of a pattern now emerging online. Across social media, GLP-1 users and their families are sharing accounts of the diabetes and obesity drugs masking serious illness, in some cases delaying diagnosis and treatment until it was too late.

Like Hinderhan, many involve colorectal cancer, a disease rising among younger Americans. Today, it’s the leading cause of cancer-related death in US adults under 50, with many patients diagnosed at advanced stages after dismissing symptoms as hemorrhoids, IBS and, now, GLP-1 use.

“I think most of what I was experiencing was probably side effects from the tumor, but nobody will ever really know if the Ozempic made me feel that way,” Hinderhan said. “It all blended together.”

From concern to crisis

Worried about her escalating symptoms, Hinderhan’s doctor switched her to Mounjaro. Like Ozempic, it’s a GLP-1 treatment that mimics hormones released after eating, helping regulate blood sugar, appetite and cravings.

The doctor said Mounjaro had fewer side effects, but for Hinderhan, they never went away. In fact, they got worse. 

“I had extreme fatigue, which was so overwhelming,” the wife and mother of four said. “It took a big toll on my life because I was just so tired.”

By February 2025, she was losing weight rapidly and began having bloody, foul-smelling stool.

Hinderhan had recently turned 45 — the recommended age to begin colorectal cancer screening — and scheduled a colonoscopy. But she later canceled it, brushing off concern about the threat.

Later, though, she took a Colorguard test — an at-home stool screening tool — that came back positive. That’s when she started getting scared.

Her doctor scheduled a colonoscopy, but she didn’t make it to the appointment. About a month before, Hinderhan developed severe pain in her side at work. 

“I went down to the ER fully anticipating that I was going to be getting my appendix taken out,” she said. “I left with the news that I had a large mass on my colon.”

The tumor was the size of a baseball, having grown so large it was nearly blocking her colon completely. The pain, she later learned, was from severe constipation.

A colonoscopy and biopsy confirmed the diagnosis: Stage 2 adenocarcinoma, along with a splenic fracture.

“I had been a hospice nurse for about eight years, and my initial thought was, ‘Oh, I’m going to die,’” she said. “Then I started thinking, ‘I should have come in sooner,’ but I didn’t really feel like there was something wrong until the last few weeks.”

When cancer red flags and GLP-1 side effects overlap

Colorectal cancer often develops silently, but early symptoms include changes in bowel movements, abdominal pain, unexplained weight loss, fatigue, anemia and blood in stool.

“Some side effects that GLP-1 agonists will cause — mostly constipation, abdominal discomfort, bloating — will overlap with symptomatic colorectal cancer,” said Dr. David Greenwald, director of Clinical Gastroenterology and Endoscopy at Mount Sinai Hospital, who did not treat Hinderhan.

“It’s really hard to differentiate them right now,” he added. “You obviously can’t use weight loss as your marker.”

A Novo Nordisk spokesperson told The Post that semaglutide, the active ingredient in Ozempic and Wegovy, has been extensively studied in clinical trials.

“We understand that some patients may experience gastrointestinal side effects, which are often temporary and can improve over time,” they said.

A representative for Eli Lilly, the manufacturer of Mounjaro, said patient safety is the company’s “top priority.”

“We actively monitor, evaluate, and report safety information for all our medicines,” they said. “Lilly’s labels for its medicines include robust, FDA-approved warnings.”

Both companies encouraged patients experiencing side effects from their medications to speak with their healthcare provider.

Greenwald said there are a few symptoms in particular that should raise concern.

“[GLP-1s] won’t cause rectal bleeding or a significant thinning or narrowing of the stool,” Greenwald said. “These need to be evaluated by a health care provider, because they aren’t normal.”

When caught early, more than 90% of colorectal cancer patients survive at least five years. Once it spreads, that number drops to about 13%, according to the American Cancer Association.

“The good news is that colorectal cancers tend to be relatively slow growing,” Greenwald said. “Delays, when they get into the matter of years, can result in later stage cancers, which are going to have worse prognosis.”

A life-changing diagnosis

Michelle Lyson is facing that reality firsthand. Five years before her cancer diagnosis, her doctor recommended she try a GLP-1 for diabetes, weight loss and polycystic ovary syndrome relief.

“It worked, I had great blood sugar control and I lost over 100 pounds,” said Lyson, 55. But she developed gastrointestinal issues almost immediately.

“Sometimes I’d be really constipated, and then other times I’d have to go four or five times a day,” Lyson said. “Whenever I would talk to my doctor about it, she would just say that’s part of Ozempic.”

In January, she noticed blood in her stool, and tests showed the mother of three from Hampton, Virginia, was anemic.

“Even at the time, my doctor and I weren’t too alarmed,” Lyson said. “I really thought all of it was the GLP-1s.”

Her doctor ordered a Cologuard test. It came back positive, prompting her to undergo a colonoscopy that revealed the disease.

“Once they told me I had cancer, I had a feeling it was going to be worse than they thought because I started putting everything together and realizing, ‘Hey, I’ve been dealing with this for five years,’” Lyson said. “It’s been there awhile.”

During surgery, doctors discovered it had spread to her peritoneum, or the thin membrane that lines the inside of the abdomen and pelvis.

“That makes it stage four,” Lyson said.

Now, she’s staring down six months of chemotherapy before another surgery to remove as much cancer as possible. During that operation, doctors will also place heated chemotherapy directly into her abdomen to target any remaining cancer cells.

Following her diagnosis, Lyson had to stop taking GLP-1s and has gained more than 40 pounds, a common experience when people go off the medications.

“It’s really discouraging,” she said. “I kept it off for so long … but I think I’d rather be alive at this point.”

Not a ‘golden ticket’ after all

After her diagnosis, Hinderhan underwent surgery to remove the tumor, part of her colon, her gallbladder and 52 lymph nodes. She suffered complications during the procedure and spent eight days in the hospital on a feeding tube, followed by months of recovery.

Doctors initially believed she would need chemotherapy, but after testing the lymph nodes, they found no signs of cancer spread.

“That, to me, was a miracle,” Hinderhan said.

Today, Hinderhan is cancer-free and back on a GLP-1 to manage her diabetes.

“I’ve lost a lot of weight, my inflammation is down, and I attribute all of that to the GLP-1,” she said. “I don’t have the symptoms that I had before.”

Despite everything, she doesn’t regret taking it.

“Looking back, I didn’t know what was making me feel the way I was feeling,” Hinderhan said. “If I had followed recommendations and gotten my colonoscopy when I was supposed to, maybe it wouldn’t have come to this.”

Lyson feels similarly: “If I knew ahead of time that I needed to watch for this, then I might have still done it,” she said.

Lyson’s message is simple: Listen to your body, follow screening guidelines — and know that GLP-1s aren’t always the “golden ticket” they’re made out to be.

“It does make you lose weight, it does quiet the food noise, but really consider if it’s worth it,” she said. 

“Because, where I’m at right now, I sit and think about all the years I worried about wanting to be thin, and I wish I could take those back and just focus on my health.”

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