The active ingredient in Ozempic is semaglutide, a long-acting GLP-1 receptor agonist peptide. Everything else in the pen—water, phenol, propylene glycol, a phosphate buffer—is inactive formulation that delivers semaglutide as a once-weekly subcutaneous injection.
Active ingredient vs formulation
A vial or pen of Ozempic contains exactly one drug. According to the FDA prescribing information:
- Active ingredient: semaglutide, a human GLP-1 receptor agonist.
- Inactive ingredients (pen): disodium phosphate dihydrate (a buffer), propylene glycol (tonicity), phenol (preservative), and water for injection.
- Inactive ingredients (single-dose syringe): disodium phosphate dihydrate, sodium chloride, and water for injection—no phenol, since a single-use format needs no preservative.
- Delivery device: a prefilled multi-dose pen (or syringe) that meters the labeled doses.
The inactive ingredients do no pharmacological work; they keep the peptide stable, sterile, and injectable. So questions about what Ozempic "does" are really questions about what semaglutide does. Anyone who wants to check an ingredient list against the primary source can look up any US drug's current label on DailyMed, the National Library of Medicine's label registry, rather than relying on third-party summaries.
Two common misconceptions are worth clearing up. First, Ozempic contains no stimulants, hormones from animal sources, vitamins, or "natural extracts"—the entire effect comes from one synthetic peptide. Second, "semaglutide" bought outside pharmacy channels is not automatically the same ingredient: the FDA reports that some unapproved products contain semaglutide sodium or semaglutide acetate, salt forms that differ from the active ingredient in the approved drug (FDA drug alert).
What semaglutide is as a peptide drug
Semaglutide is an engineered analogue of GLP-1, a natural gut hormone that signals fullness and regulates blood sugar. The label describes it as having 94% sequence homology to human GLP-1, with amino acid substitutions and a fatty-acid chain that binds albumin—the modification that stretches a hormone lasting minutes into a drug lasting a week.
Acting on GLP-1 receptors, semaglutide augments insulin secretion when glucose is high, suppresses glucagon, slows gastric emptying, and reduces food intake—the core incretin actions mapped in Drucker's review of GLP-1 mechanisms (Cell Metabolism, 2018). Because the insulin effect is glucose-dependent, the molecule behaves differently from older diabetes drugs that push insulin regardless of blood sugar. The scale of its effect is well quantified: in STEP 1 (n=1,961), the 2.4 mg weekly dose produced 14.9% mean weight loss vs 2.4% for placebo over 68 weeks, and in SELECT (n=17,604) it cut major cardiovascular events by 20% in people with heart disease and overweight or obesity. The same molecule also carries labeled warnings—GI side effects, acute pancreatitis, gallbladder disease, and a boxed warning based on rodent thyroid C-cell tumors—which is why it is dosed through a defined titration schedule under a prescription. More detail lives on the semaglutide catalog page.