GLP-1s during cancer treatment: What triggers a pause?

Reddit user @Go-downtotheseaagain described a scenario in the r/breastcancer thread that oncologists are likely to encounter more often in 2026: “I had been on Ozempic for over a year when I got diagnosed, and started chemo," she began, noting that her oncologist and PCP initially continued the medication. After several infusions brought persistent nausea, vomiting, and poor intake, her Ozempic dose was reduced from 1.0 mg to 0.5 mg. 

Board-certified physician Syed Ahmad Raza, MD, says, “Establishing the indication of [the] GLP-1 drug is the most important step after the diagnosis of cancer is made, whether it is being used for diabetes or obesity. Moreover, nutrition, recent weight patterns, blood sugar levels, kidney functions, and gastrointestinal symptoms are assessed.”

A 2025 study of 343 patients receiving neoadjuvant chemoimmunotherapy for early stage TNBC found that only 7.5% of patients were taking a GLP-1 drug throughout treatment.^[] Their pathologic complete response rate was lower, although major baseline differences and the small exposed cohort preclude causal conclusions.

“The site of cancer and the recommended cancer treatment with its side effects [are] ascertained to make sure that it is not going to interact with the GLP-1 analogues in any negative way. Let me tell you that the diagnosis of cancer and its treatment do not mean that GLP-1 drug[s] must be stopped. The decision is individualized, keeping in view the [aforementioned] parameters,” Dr. Raza adds.

Board-certified urologist Arthur Burnett II, MD, FACS says, “The cancer itself matters because each disease presents different nutritional and treatment-related challenges.” 

Breast cancer

Obesity is associated with more postoperative complications after breast cancer surgery, particularly reconstruction, as well as higher risks of local recurrence and mortality.^[] This makes long-term weight management clinically relevant, although evidence supporting GLP-1 use during active chemotherapy remains limited.

However, clinicians advise caution. 

Neil Iyengar, MD, does not recommend starting GLP-1 therapy after being diagnosed with breast cancer or while undergoing chemotherapy, according to the Breast Cancer Research Foundation.^[] His concerns include worsening side effects, such as nausea.

New observational findings are reassuring, though. A 2026 JAMA Network Open cohort study involving propensity score-matched data from 841,831 patients linked GLP-1 exposure with improved survival and reduced recurrence among patients with obesity or type 2 diabetes.^[] Treatment exposure was not randomized, leaving residual confounding.

Colorectal, liver, pancreatic, and lung cancers

At the 2026 ASCO Annual Meeting, a propensity-matched analysis compared GLP-1 therapy with DPP-4 inhibitors after diagnosis of stage I–III cancers.^[] Progression to stage IV disease was lower with GLP-1 therapy in non-small cell lung cancer, breast cancer, colorectal cancer, and hepatocellular carcinoma. Colorectal progression occurred in 13.4% vs 22.2%, with an HR of 0.69. Pancreatic, prostate, and renal cancers showed nonsignificant trends.

Julie Gralow, chief medical officer of ASCO, noted during a press briefing, “We’ll need a randomized trial to prove causation beyond association.” 

According to Dr. Burnett, “Patients with colorectal, pancreatic, or hepatobiliary cancers are often at greater risk for digestive complications, malabsorption, and unintended weight loss, making careful monitoring particularly important.” 

Thyroid cancer

As for other cancer variants such as thyroid tumors, Dr. Burnett notes, “For patients with medullary thyroid carcinoma or multiple endocrine neoplasia type 2, GLP-1 receptor agonists remain contraindicated according to current prescribing guidance. Ultimately, management should be individualized rather than based solely on the cancer diagnosis.”

Treatment-associated toxicity decides the safety of GLP-1 

Apart from tumor site, according to Dr. Raza, the decision to continue GLP-1 agonists also depends greatly on chemo-associated toxicities and nutritional risk. “The approach is primarily guided by the toxicities associated with the treatment and nutritional risk. The site of tumor, although taken into consideration, is not the primary factor to decide the continuation or discontinuation of GLP-1 analogues. So, the approach stays more or less the same if it is breast, colorectal, pancreatic, hepatobiliary, or thyroid cancer,” he says.

He advises prioritizing hydration, nutritional status, and functional capacity.

Procedures, radiation, and imaging

Dr. Raza warns that with “cancer of the stomach and colon, …malnourished and cachectic patients are at an increased risk of worsening nausea, vomiting, diarrhea, constipation, dehydration, and weight loss” when they undergo radiation therapy combined with chemotherapy. 

However, experts advise avoiding automatic discontinuation before surgery.

Multisociety clinical practice guidance released in 2024 states that most patients should continue GLP-1 therapy.^[] Patients undergoing dose escalation or experiencing significant gastrointestinal symptoms require individualized aspiration-risk assessment, a preprocedure liquid diet, gastric ultrasound, or delayed surgery.

It might also be advisable to document GLP-1 exposure before FDG PET/CT, since various reports describe atypical uptake in skeletal muscle, myocardium, and brown fat.^[][]

However, researchers currently advise documenting patients’ medication use rather than routine interruption. “Recognising the characteristic uptake associated with GLP-1 agonists helps avoid unnecessary anxiety and interventions,” Peter Strouhal, MD, said.^[]