Semaglutide lingers in the blood for a week thanks to one fatty tail
Semaglutide, sold as Ozempic, Rybelsus and Wegovy, mimics a gut hormone that tells the body it has eaten. Natural GLP-1 breaks down fast, but chemists swapped two amino acids and bolted on an 18-carbon chain, giving the drug a half-life of about seven days. In 2023 Americans filled over 25 million prescriptions.
The molecule is a trimmed copy of human GLP-1 missing its first six amino acids. Replacing one alanine blocks an enzyme called dipeptidyl peptidase-4 from chopping it up, and the long fatty side chain makes it stick to albumin in the blood, so it circulates for roughly 165 to 184 hours. Novo Nordisk developed it, and it was approved in the United States in 2017, in the European Union, Canada and Japan the following year, and in Australia in 2019. It appears on the World Health Organization's List of Essential Medicines.
Its effects are spread across the body. In the pancreas it prompts insulin release only when glucose is present and holds back glucagon, which reduces the liver's sugar output. It also crosses into the hypothalamus, stimulating neurons that signal fullness while quieting those that drive hunger, and it appears to restore the brain's response to leptin, a satiety hormone that many people with obesity stop registering. Slower stomach emptying adds to the sense of fullness.
Approved uses keep widening. Beyond type 2 diabetes and weight management, US regulators in 2025 cleared it for a form of fatty liver inflammation with fibrosis and for cutting cardiovascular risk in high-risk diabetic adults, and in December 2025 they approved a tablet form of Wegovy. The most common side effects are gastrointestinal, usually worst during the first 8 to 12 weeks of dose increases. It carries a US boxed warning about thyroid tumours, based on rodents whose thyroids are dense with the relevant receptors; human thyroids have few, and the risk is considered unlikely in people.
Stopping has consequences. A 2025 systematic review found that people regained on average 67% of the weight lost within a year of quitting. An anthropological study of three Danish general practices challenged the idea of an easy shortcut, finding patients and doctors constantly adjusting doses and working hard to keep access. A meta-analysis of ten studies found the rival drug tirzepatide produced greater weight loss, though with more serious adverse events.
Source: Semaglutide
