Stanford researchers have identified a tiny peptide produced naturally in the human body that slashes appetite in animals without the nausea or muscle loss that plagues existing weight-loss drugs. The discovery, published in Nature in March 2025, offers a rare glimpse at a fundamentally different mechanism for treating obesity — and a company is already being built around it.
The peptide, called BRINP2-related peptide, or BRP, is only 12 amino acids long. It is encoded by a gene called BRINP2 and is measurable in human cerebrospinal fluid at concentrations of 700 picomolar to 3 nanomolar, confirming it is not an artifact of drug administration but a genuine molecule the body makes on its own. When researchers at Stanford's School of Medicine injected it into lean mice and minipigs, food intake dropped by as much as 50% within an hour. Obese mice treated daily for two weeks lost an average of 3 grams while control animals gained about 3 grams — researchers attributed the weight loss to fat loss, based on the absence of changes in movement and other behavioral markers.
The critical difference from existing drugs is what BRP does not do.
GLP-1 agonists like semaglutide and tirzepatide act on receptors in the gut, pancreas, and brain, producing impressive weight-loss results but also a well-documented set of side effects: severe nausea, vomiting, and the loss of lean muscle mass alongside fat. BRP operates independently of the GLP-1 receptor, the leptin pathway, and the melanocortin-4 receptor, the three pathways most targeted by current obesity drugs. It activates a distinct signaling cascade in hypothalamic neurons, specifically the cAMP-PKA-CREB-FOS pathway, and its effects appear concentrated in the hypothalamus, the brain's appetite control center.
In behavioral studies, treated mice and pigs showed no differences from controls in movement, water intake, anxiety-like behavior, or fecal production. No aversion to the compound was observed, even when it was administered before feeding. "We did not see nausea or aversion in our studies," said Jonathan Svensson, one of the paper's senior authors, in a Stanford press release.
The discovery began with computation. Svensson and graduate student Marco Coassolo built a tool called Peptide Predictor that scans entire proteomes for sequences that resemble hormonal peptides. Their code is freely available on GitHub. They ran it against all 20,000 human protein-coding genes, looking for proteins that were secreted, contained multiple cleavage sites, and showed evolutionary conservation. The screen narrowed to 373 candidate prohormones and predicted 2,683 unique peptide fragments they might generate. One of those fragments, derived from the BRINP2 protein, caught their attention because its structure suggested it would be bioactive.
They then screened 100 peptides for activity in hypothalamic neurons. BRP increased neuronal activity tenfold over controls. GLP-1, by comparison, produced a threefold increase. When they traced BRP's mechanism, they found it activated FOS, a transcription factor that governs cell memory and gene expression changes in response to signals. The receptor that BRP binds to on the surface of those neurons remains unknown — the most important open question the team has left for the next phase of research.
Svensson is a co-founder of Merrifield Therapeutics, a company formed to advance BRP toward human clinical trials. The company is not yet in trials, and no timeline has been announced. The Nature paper lists NIH funding (grants R01DK125260, P30DK116074, K99AR081618, and GM113854).
There is substantial distance between an animal result and an approved drug. GLP-1 research took more than a decade to move from early animal data to the blockbuster class of medications available today. The unknowns around BRP are significant: the unknown receptor is the most obvious, but durability of effect, optimal delivery method, and human safety data do not yet exist. BRP is also a peptide, which typically requires injection and has a shorter half-life than small-molecule drugs — though this could change if a stable oral analog is developed.
What makes the BRP story noteworthy is not just the animal data but the specificity of the mechanism and the absence of the side-effect profile that defines the current obesity drug market. If a molecule can produce meaningful appetite suppression without nausea, without muscle loss, and without acting on the pancreas or gut, it would represent a genuinely different approach in a field that has been converging on GLP-1 for years. The fact that it is already present in human cerebrospinal fluid suggests the body already has a system for regulating appetite through this pathway — researchers have simply found a way to amplify it.
The ScienceDaily article that circulated this week was based on the March 2025 Nature paper and Stanford's subsequent press materials. The underlying research is 13 months old. What Merrifield Therapeutics does with it next — and how quickly — will determine whether BRP becomes a footnote in the history of metabolic science or the foundation of the next generation of obesity medicine.
