What Comes After Ozempic? A Tiny Boston Startup Is Trying to Treat Obesity Without GLP-1

Ozempic, Wegovy, and Mounjaro proved a single gut-hormone receptor could reshape a country's waistline. The next wave of obesity drugs is being judged on a different ledger. The bet is no longer just how many pounds come off, but how much of what comes off is muscle, and a tiny Boston startup called Mwyngil (mwin-GULL) is staking its entire pitch on that second column.

Mwyngil Therapeutics disclosed 4-week preclinical data this week showing its lead pill, an oral, brain-penetrant inverse agonist of a receptor called GPR75, cut body weight in obese mice by up to 25% over a month while preserving lean mass. The company says the same animals showed lower fasting blood sugar, lower HbA1c, lower inflammatory markers, and improved cholesterol. The framing is "quality weight loss," a deliberate break from the GLP-1 gold rush that has come to define the category.

CEO Luba Greenwood told STAT that the bet on a different target was the point. "I was not interested in another 'me too' GLP-1, or GLP-1 plus something. … That's not very interesting science."

GLP-1, the gut-hormone receptor that Ozempic, Wegovy, and Mounjaro target, has produced the first generation of genuinely mass-market obesity drugs. The side effect that has trailed them is the loss of muscle along with fat. Industry coverage pegs the share of lean mass lost on Wegovy and Zepbound at roughly 20% to 40% of total weight lost, according to a synthesis by AllSci, and that gap is what Mwyngil is designing its scoreboard around.

The scientific case for GPR75 is real, but it is not new. A 2021 study of roughly 640,000 people linked loss-of-function variants of the gene to lower body-mass index and reduced obesity risk, and GPR75 knockout mice are resistant to diet-induced weight gain. AstraZeneca and Regeneron signed a GPR75 collaboration that same year, a reminder that the target has been on big-pharma radar for half a decade with no disclosed human efficacy yet. Mwyngil's twist is the chemistry: a brain-penetrant, allosteric inverse agonist, a small molecule designed to hit the receptor in the central nervous system where appetite is regulated, in pill form.

The mouse numbers Mwyngil is leaning on are company-disclosed preclinical data, not human readouts. Fat mass dropped 33% to 50%, epididymal white adipose tissue shrank up to 1.5-fold, and the lead molecules showed functional potency in the lower double-digit nanomolar range in a cell-based assay, with oral and brain exposure consistent with central target engagement. None of that is in a patient yet. Mwyngil has not disclosed when a first-in-human study would start, has not shared safety or tolerability data beyond the animal models, and the lean-mass comparison to Wegovy and Zepbound is a cross-trial framing rather than a head-to-head study.

Rivus Pharmaceuticals reported muscle-sparing data for its oral GLP-1 RV-8451 in non-human primates at the American Diabetes Association meeting this year, and the amylin class is in early human trials, both aimed at the same lean-mass-preservation column. Mwyngil is further back on the same scoreboard, with a four-week mouse study as its first public readout. The non-GLP-1 obesity pipeline has produced more press releases than approved drugs.

Mwyngil in-licensed the GPR75 program from Expert Systems Inc. in November 2025. Its broader pipeline also includes brain-penetrant PTP-1B and NLRP3 programs. The extra programs frame GPR75 as a portfolio play, not a single bet. The "quality weight loss" frame is the one every next-gen obesity startup now reaches for, and the field has learned to ask which column a new readout is being scored on, what stage of evidence it is at, and whether the lean-mass claim is a head-to-head study or a cross-trial cherry-pick. Mwyngil's first answer is a press release and a CEO interview. The next one is a Phase 1.