GLP-1 Drugs: Benefits, Side Effects & Long-Term Risks for Diabetes & Weight Loss

Widely used medications initially developed for type 2 diabetes are now also popular for weight loss, but a growing body of research is clarifying both their benefits and potential risks. These drugs, known as glucagon-like peptide-1 receptor agonists (GLP-1RAs), and related medications like tirzepatide, are under increasing scrutiny as their long-term effects become clearer.

GLP-1RAs work by mimicking the effects of a natural hormone, GLP-1, which regulates blood sugar and appetite. They act on receptors primarily found in the brain, pancreas, and gastrointestinal tract, leading to improved glycemic control and weight reduction. However, stimulation of these receptors can also trigger adverse responses, according to a recent review published in the Journal of Clinical Investigation.

Gastrointestinal Effects: The Most Common Side Effects

The most frequently reported side effects of GLP-1RAs are gastrointestinal in nature. A systematic review of 39 randomized controlled trials found increased risks of vomiting, nausea, constipation, and diarrhea in individuals taking these medications compared to those receiving a placebo. Specifically, nausea was observed in 19% of type 2 diabetes patients treated with GLP-1RAs, and vomiting in 7.6%.

Tirzepatide, which activates both the GIP receptor and the GLP-1 receptor, has demonstrated even greater efficacy for weight loss and glucose lowering than GLP-1RAs alone. However, studies suggest that GIP co-agonism doesn’t necessarily reduce the risk of gastrointestinal side effects. In fact, a large cardiovascular outcomes trial indicated that recipients of tirzepatide reported vomiting, diarrhea, and nausea at higher rates than those taking selective GLP-1RAs. A systematic review also reported that tirzepatide conferred the highest risk of vomiting.

Delayed gastric emptying, a common effect of GLP-1RAs, can increase the volume of retained stomach contents, potentially raising concerns about aspiration during medical procedures. However, evidence directly linking this to aspiration pneumonia remains limited and sometimes contradictory.

Pancreatic and Thyroid Concerns

Initial concerns about an increased risk of acute pancreatitis and pancreatic cancer have largely been alleviated by long-term randomized trials, which have not established a causal link. However, researchers emphasize the importance of continued monitoring and careful reporting due to potential biases and the complexities of diagnosing these conditions.

More recently, concerns have emerged regarding a potential link between GLP-1RA use and medullary thyroid carcinoma, stemming from rodent studies showing increased calcitonin secretion and C-cell growth. While GLP-1 receptors are generally not detected in healthy human thyroid C-cells, they are often found in hyperplastic C-cells and medullary thyroid carcinomas. Data from France suggest a higher risk of medullary thyroid carcinoma in individuals treated with GLP-1RAs compared to other glucose-lowering agents. A meta-analysis also reported diagnoses of this cancer in patients taking these medications, leading to a contraindication for individuals with a personal or family history of the condition. However, the absolute number of cases remains low, and findings for other thyroid cancer subtypes are inconsistent.

Ocular and Psychiatric Safety Signals

Safety signals have also been identified in relation to ocular and psychiatric health. A cardiovascular outcomes trial showed that semaglutide treatment increased the risk of retinopathy complications, particularly among those with pre-existing proliferative or preproliferative retinopathy. However, other trials that excluded participants with pre-existing retinopathy have not shown similar results.

There have also been reports of non-arteritic anterior ischemic optic neuropathy (NAION) associated with semaglutide use. While the overall incidence is relatively low (14.5 per 100,000 person-years), studies have shown a modest increased risk attributable to the medication. Further research is needed to determine a causal relationship.

The relationship between GLP-1RAs and mental health is complex and remains under investigation. Obesity and type 2 diabetes are themselves risk factors for depression and suicidal ideation. Some studies have suggested a potential link between GLP-1RA use and an increased risk of anxiety, suicidal behavior, and major depression, while others have reported decreased depression risk or even antidepressant effects. Meta-analyses have yielded conflicting results, highlighting the need for more research and standardized outcome definitions.

The Need for Vigilance and Comprehensive Evaluation

Given the widespread use of GLP-1RAs for both obesity and type 2 diabetes, a comprehensive evaluation of even common side effects, like gastrointestinal issues, remains limited. Improved pharmacovigilance and standardized adverse event reporting are crucial for a better understanding of the risk-benefit profiles of individual GLP-1RAs and their specific indications. Particular attention should be paid to diverse populations, including older adults, individuals with kidney disease, pregnant patients, and those at risk of losing lean muscle mass during rapid weight loss.

As of October 15, 2025, these medications represent a significant advancement in the treatment of obesity and type 2 diabetes, but ongoing research and careful monitoring are essential to ensure their safe and effective use.