GLP-1 Drugs Show Broader Effects Through Gene Expression and Gut Microbiome Interactions

Researchers at the Salk Institute have identified a protein that connects GLP-1 agonist drugs to long-term genomic responses promoting pancreatic health, while emerging evidence suggests the gut microbiome may shape individual responses to these medications. The findings, published in Proceedings of the National Academy of Sciences on March 4, 2026, help explain the broad effects of drugs originally developed to treat diabetes.

The Salk team identified a protein called Med14—part of a larger protein complex called Mediator—that enables GLP-1-dependent changes in gene expression leading to pancreatic health benefits. The researchers screened for regulatory proteins that can activate advantageous gene programs during prolonged GLP-1 use, focusing on how these drugs promote viability and stress resistance in pancreatic beta cells.

Unlike human-made GLP-1 hormones that appear and disappear quickly around mealtimes, artificial GLP-1 receptor agonists stick around much longer. The researchers suspect this longer-term presence may explain some of the broader benefits of GLP-1 drugs. When the team mutated Med14 to make it resistant to phosphorylation, the gene expression patterns associated with prolonged GLP-1 drug exposure disappeared in a pancreatic beta cell line and in beta cells of a mouse model. With working Med14, helpful gene programs were activated—supercharging pancreatic beta cells to grow and better handle sugar-rich environments after meals.

Some of the genes regulated by Med14 phosphorylation are known to be linked to type 2 diabetes susceptibility in humans. The study was funded by federal research grants from the National Institutes of Health and private philanthropy.

A review published in the British Journal of Clinical Pharmacology examined the bidirectional relationship between GLP-1 receptor agonists and the gut microbiome. More than 500 million people worldwide live with type 2 diabetes mellitus, and obesity rates continue to rise. The review noted that an important unanswered question is why some individuals respond differently to these therapies than others.

The gut microbiome helps regulate GLP-1, a hormone secreted by enteroendocrine L-cells in the intestine. When gut bacteria break down dietary fiber, they produce short-chain fatty acids (SCFAs), including acetate, propionate, and butyrate. SCFAs activate G-protein-coupled receptors 41 and 43, also known as free fatty acid receptor 3 and free fatty acid receptor 2, on L-cells and engage intracellular signaling pathways. This signaling can stimulate GLP-1 release through mechanisms that include modulation of intracellular calcium and cyclic adenosine monophosphate (cAMP) signaling.

Bile acids also regulate GLP-1. Primary bile acids such as cholic acid and chenodeoxycholic acid are converted by intestinal bacteria into secondary bile acids, such as deoxycholic acid and lithocholic acid. These activate Takeda G-protein receptor 5 (TGR5), increasing cAMP and promoting GLP-1 secretion. In contrast, activation of the farnesoid X receptor (FXR) suppresses GLP-1 synthesis.

Clinical and preclinical studies report that GLP-1RA treatment may enrich beneficial bacteria such as Akkermansia muciniphila and, in some studies, increase Bacteroidetes while reducing Firmicutes or inflammation-associated taxa. Some trials report increased microbial alpha diversity and beta diversity, whereas others find minimal shifts, suggesting variability between individuals and differences in study design, duration, diet, and concomitant therapies.

In patients with type 2 diabetes mellitus, liraglutide has been associated with lower glycated hemoglobin (HbA1c) and modest changes in body weight and body mass index (BMI), alongside increased abundance of Akkermansia muciniphila. In high-fat diet animal models, semaglutide has been associated with a reduced Firmicutes-to-Bacteroidetes ratio, lower inflammatory cytokines, and improved glucose tolerance.

Microbial changes may not reflect only direct drug effects. Reduced caloric intake and weight loss can independently alter microbial communities, and medications such as metformin also reshape the microbiome, complicating interpretation.

The drugs, which include brands like Wegovy and Zepbound, essentially mimic gut hormones to function as appetite suppressants. Roughly 20 million to 25 million patients worldwide could be taking a GLP-1 manufactured by Novo Nordisk or Eli Lilly and Company, according to an estimate from February 2026. Among Americans, 18% of adults say they've taken a GLP-1 drug at some point, and 12% say they're currently taking one, according to a KFF Health Tracking Poll published on Nov. 14.

Users report finding themselves drinking less alcohol, spending less on groceries or no longer craving junk foods. Others have reported side effects like gastrointestinal distress, shrinking muscle mass and sagging skin from the weight loss. GLP-1s typically have a list price of more than $1,000 per dose, and while those prices can drop significantly under some health insurance plans, coverage can be inconsistent across insurers. Some users report rapid weight gain after stopping GLP-1s, and the drugs' longer-term side effects aren't particularly well-studied yet.

Patient and insurer spending on GLP-1s in the U.S. rose to $71.7 billion in 2023, up from $13.7 billion in 2018, according to an April 2025 research letter from American Medical Association researchers. Some analysts predict that GLP-1 sales will rise to $100 billion by 2030. Companies like Pfizer, AstraZeneca and Roche are now developing competitor medicines for weight loss.