GLP-1s and Tirzepatide: Weighing Benefits Against Emerging Risks

Widely used medications like GLP-1 receptor agonists (GLP-1RAs) and tirzepatide have become popular for weight loss and diabetes management. While offering significant benefits, emerging evidence is clarifying potential side effects and risks that clinicians and patients should be aware of long-term.

How GLP-1s and Tirzepatide Work

Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are incretin hormones that play a role in regulating blood sugar and appetite. GLP-1 has demonstrated therapeutic potential in reducing body weight and lowering plasma glucose levels. GLP-1RAs are developed based on this parent compound, acting through the GLP-1 receptor (GLP-1R) found in the brain, pancreas, and gastrointestinal (GI) tract. These medications provide beneficial effects on glycemic control and weight, but can similarly induce adverse responses.

Common Side Effects: Gastrointestinal Concerns

Gastrointestinal (GI) adverse effects are the most frequently reported side effects of GLP-1RAs. A systematic review of 39 randomized controlled trials (RCTs) showed increased risks of vomiting, nausea, constipation, and diarrhea in individuals without diabetes compared to placebo. Another review of 38 RCTs involving patients with type 2 diabetes (T2D) observed nausea in 19% of participants and vomiting in 7.6% [1]. Rapid dose escalation of semaglutide in a phase II trial led to greater weight loss but also more adverse events.

Tirzepatide, a co-agonist of the GIP receptor and GLP-1R, is more effective for weight loss and glucose lowering than GLP-1RAs alone, with a similar adverse event profile. While animal studies suggest GIP receptor agonists don’t induce vomiting like GLP-1RAs, clinical trials indicate tirzepatide may slightly increase the risk of vomiting compared to selective GLP-1RAs. A large cardiovascular outcomes trial found higher proportions of tirzepatide recipients reported vomiting, diarrhea, and nausea [1].

Delayed gastric emptying, associated with GLP-1RAs, may increase the volume of retained gastric contents before procedures, though a direct link to aspiration pneumonia remains unclear.

Emerging Safety Signals

Pancreatic and Biliary Concerns

Earlier concerns about acute pancreatitis and pancreatic cancer have been largely alleviated by long-term randomized trials that haven’t confirmed a causal association, though continued monitoring is recommended. Some analyses also suggest an increased risk of biliary disease, particularly cholelithiasis, with GLP-1RA therapy.

Thyroid Cancer Risk

Concerns about medullary thyroid carcinoma arose from rodent studies. While GLP-1R expression is generally not detected in healthy human thyroid C cells, it is often found in human medullary thyroid carcinomas. Data from France suggest a potentially higher risk of medullary thyroid carcinoma in people treated with GLP-1RAs compared to other glucose-lowering agents. A meta-analysis also reported diagnoses of medullary thyroid carcinoma in patients taking GLP-1RAs, making it a contraindication for treatment [1]. However, absolute event numbers remain low, and findings for other thyroid cancer subtypes are inconsistent.

Ocular and Psychiatric Effects

Semaglutide treatment has been linked to increased retinopathy complications in cardiovascular outcomes trials, particularly among those with pre-existing retinopathy. A higher risk of non-arteritic anterior ischemic optic neuropathy (NAION) has also been reported with semaglutide, though the incidence remains relatively low.

Obesity and T2D are risk factors for depression and suicidal ideation. Some studies have found a two-fold increased risk of anxiety and suicidal behavior and a three-fold increased risk of major depression among GLP-1RA users, while others report decreased depression risk or no association with suicidal ideation [1]. Further research is needed to clarify these potential links.

Individualized Treatment and Ongoing Monitoring

Given the widespread use of GLP-1RAs and tirzepatide, comprehensive evaluation of even common GI adverse effects remains limited. Improved pharmacovigilance and standardized adverse event reporting are crucial for understanding the risk-benefit profiles for individual medications and indications. Particular attention should be paid to diverse populations, including older adults, individuals with advanced renal disease, pregnant patients, and those at risk of lean mass loss during rapid weight reduction.

Key Takeaways

• GLP-1RAs and tirzepatide are effective for weight loss and glucose control but come with potential side effects.
• Gastrointestinal issues are the most common adverse effects.
• Emerging safety signals related to thyroid cancer, ocular health, and psychiatric outcomes require further investigation.
• Individualized treatment and careful monitoring are essential.