Semaglutide

Anyone trying to understand the GLP-1 family starts with semaglutide: no other mono-agonist has been studied this thoroughly.

Key facts:

• Structure: an altered human GLP-1 analog whose fatty acid side chain strengthens binding to albumin.
• Half-life: around seven days, which made it the reference in studies for one administration per week with steady plasma levels.
• Receptor: GLP-1 only, with no GIP or glucagon component.
• Numbers: in the STEP trials, mean weight loss at the highest dose over 68 weeks came to roughly 15 percent.

Where the molecule acts in research models: at GLP-1 receptors of the pancreatic beta cells, of the brain and of the gut. Three central effects follow from that, namely delayed gastric emptying, stronger satiety signaling in the hypothalamus and insulin secretion that depends on the glucose level.

Precisely because only one receptor is engaged, semaglutide works as a clean tool whenever the GLP-1 pathway alone is the object of study; the dual and triple agonists of the family, such as tirzepatide and retatrutide, bring additional receptors into play. Study protocols began with low concentrations and stepped up weekly to keep nausea low. Below you find the landmark STEP 1 trial, data on combination with behavioral therapy, cardiovascular endpoints and the direct comparison with tirzepatide.

Semaglutide is the most thoroughly investigated member of its class and, according to the studies, well tolerated overall; the profile of a pure GLP-1 agonist is clearly outlined and shaped by gut effects.

• Stomach and bowel: nausea, vomiting, diarrhea and constipation are reported most often, mainly at the start and while the dose is being raised; in the STEP trials, slow titration softened this considerably.
• Fluids: less appetite in the studies often meant less food and fluid, and the literature describes a higher risk of dehydration.
• Muscle mass: alongside fat, the studies record a share of muscle mass lost as well.
• Gallbladder and injection site: gallbladder complaints are documented during rapid weight loss, plus mild local irritation.
• Long term: despite the broad clinical base, data on use over very long periods are missing.

This summary is no substitute for medical advice.

• Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1) - the trial with 1961 participants over 68 weeks.
• Semaglutide as an Adjunct to Intensive Behavioral Therapy (STEP 3) - tests what semaglutide adds on top of intensive behavioral therapy.
• Semaglutide and Cardiovascular Outcomes in Patients with Type 2 Diabetes (SUSTAIN-6) - cardiovascular endpoints over 104 weeks in type 2 diabetes.
• Tirzepatide versus Semaglutide Once Weekly (SURPASS-2) - the direct comparison of both molecules in a type 2 diabetes population.