What Is Actually in an Ozempic Pen?

"What is Ozempic made of" is a reasonable question to have zero confident answer to — the drug is famous, but the actual contents of the pen aren't something most patients ever see written out. They're not secret, either. Novo Nordisk's FDA-approved prescribing information lists them explicitly, in the section labeled DESCRIPTION¹. Here's exactly what's in there, in plain language.

The active ingredient: semaglutide

Semaglutide is a GLP-1 receptor agonist — a lab-made analog of a hormone your gut already produces (GLP-1) that's been chemically modified to last in the body for about a week instead of a few minutes. Per the label, its peptide backbone is produced by yeast fermentation, then modified at two positions: one attaches a fatty acid chain that lets the molecule bind to albumin in the blood (which is what stretches its action out to roughly a week), and another stabilizes it against a body enzyme (DPP-4) that would otherwise break it down fast¹. The molecular formula, per the label, is C187H291N45O59, at a molecular weight of 4113.58 g/mol¹. That's the part doing the pharmacological work — everything else in the pen exists to keep that molecule stable, sterile, and comfortable to inject.

The inactive ingredients — and what each one actually does

Per 1 mL of solution, the Ozempic prefilled pen (the standard, refillable-click multi-dose pen — 2 mg, 4 mg, and 8 mg strengths) contains, beyond semaglutide itself¹:

- **Disodium phosphate dihydrate (1.42 mg)** — a buffer. Its job is to hold the solution's pH steady near 7.4, which is close to your blood's natural pH. A stable pH keeps the semaglutide peptide from degrading in the pen and makes the injection less irritating to the tissue it goes into. - **Propylene glycol (14 mg)** — a tonicity agent. It adjusts the solution's osmotic pressure to roughly match your body's own fluids, so the injection doesn't cause the stinging or tissue disruption an out-of-balance solution would. Propylene glycol is a common pharmaceutical additive (also used in some oral medications and topical products) and is a different substance from the antifreeze compound ethylene glycol that shares part of the name. - **Phenol (5.5 mg)** — a preservative. This is the ingredient most likely to raise an eyebrow, because "phenol" also names a caustic industrial chemical. In an FDA-approved injectable at this concentration, it's serving a narrow, well-precedented purpose: killing off any bacteria introduced during the pen's repeated use, since one pen is punctured with a fresh needle multiple times over its use life. The same small dose of phenol has been used as a preservative in insulin pens for decades. - **Water for injections** — the solvent. Sterile, pyrogen-free water that the other ingredients are dissolved in.

The label also notes the finished solution has a pH of approximately 7.4, and that hydrochloric acid or sodium hydroxide may be added during manufacturing to fine-tune it to that target¹ — not ingredients you inject in any meaningful quantity, just a manufacturing step to land the buffer where it needs to be.

The single-dose syringe is formulated slightly differently

Ozempic also comes in a single-dose prefilled syringe (0.25 mg, 0.5 mg, and 1 mg strengths), and its inactive-ingredient list is shorter: disodium phosphate dihydrate, sodium chloride, and water for injection — no phenol, no propylene glycol¹. That's not an inconsistency; it's the formulation matching the product. A single-dose syringe is used once and discarded, so there's no repeated-puncture contamination risk to guard against, which is why the phenol preservative isn't needed. Sodium chloride (plain salt) does the tonicity job propylene glycol does in the multi-dose pen.

The same general approach applies to Wegovy — verified against its own label

Wegovy is also semaglutide, at higher doses, approved for weight management rather than diabetes (see Ozempic vs Wegovy for how the two actually differ). Checking Wegovy's own FDA-approved prescribing information confirms it uses the identical inactive-ingredient logic: the WEGOVY FlexTouch multi-dose pen contains disodium phosphate dihydrate, phenol, propylene glycol, and water for injections, while the single-dose prefilled syringe swaps in sodium chloride and drops the phenol and propylene glycol — the exact same pen-vs-syringe pattern as Ozempic². Mounjaro and Zepbound (tirzepatide) are a different molecule with their own separate FDA-approved label, and this article isn't asserting their specific excipient list — the reliable way to check any brand's exact formulation is the DESCRIPTION section of that product's own current prescribing information, not an assumption carried over from a different drug.

Compounded versions don't follow this label at all

This is the detail that matters most if you're comparing a brand-name pen to a compounded product. Everything above is the FDA-approved formulation — it's tested, standardized, and legally required to match what's on the label for every Ozempic pen manufactured. Compounded semaglutide is not required to follow that same recipe, because it isn't the FDA-approved product; a compounding pharmacy can legally use a different salt form, different buffers, a different preservative approach, or no preservative at all, and still be operating within the law that governs compounding (see is compounded semaglutide legit and safe for what that oversight actually looks like, and compounded vs. brand-name cost for what the price difference buys you). Neither "compounded" nor "brand" is automatically the safer formulation in the abstract — but they are provably different formulations, and the FDA label above is the only one of the two that's a matter of public record down to the milligram.