Wegovy’s active ingredient is semaglutide, a modified version of a hormone your body naturally produces called GLP-1. Each prefilled pen also contains a short list of inactive ingredients: disodium phosphate dihydrate, sodium chloride (salt), and water for injection. That’s it. The formulation is preservative-free, which is one reason Wegovy comes in single-dose pens rather than multi-dose vials.
The Active Ingredient: Semaglutide
Semaglutide is a 31-amino-acid peptide, essentially a small protein chain that closely resembles human GLP-1 (glucagon-like peptide-1). Your gut releases natural GLP-1 after you eat, but it breaks down in the body within minutes. Semaglutide has been chemically altered so it lasts much longer, roughly a full week, which is why Wegovy is a once-weekly injection.
Two key modifications make this possible. First, one amino acid early in the chain has been swapped out for a synthetic one that resists the enzymes that normally chop up GLP-1. Second, a fatty acid chain is attached to the peptide through a chemical linker at a specific point on the molecule. That fatty acid grabs onto albumin, a protein in your blood, which acts like a slow-release carrier and shields semaglutide from being cleared by your kidneys.
How Semaglutide Is Manufactured
The semaglutide in Wegovy is not synthesized purely in a lab. It starts in living yeast cells. Specifically, manufacturers use recombinant DNA technology in Saccharomyces cerevisiae, the same species of yeast used in brewing and baking. The yeast is engineered to produce a precursor version of the semaglutide peptide during fermentation.
After fermentation, that precursor is isolated and purified, then put through a chemical modification step. This is where the fatty acid and its linker are attached to the peptide backbone. A final step joins the remaining piece of the peptide chain to complete the molecule. The result is a highly specific, pharmaceutical-grade compound that’s identical from batch to batch.
Inactive Ingredients
The inactive ingredients in Wegovy serve simple roles. Disodium phosphate dihydrate (1.42 mg per mL) acts as a buffer to keep the solution at a stable pH of about 7.4, which matches your body’s natural pH and minimizes irritation at the injection site. Sodium chloride (8.25 mg per mL) adjusts the solution’s tonicity so it’s compatible with your tissues. The rest is water for injection. Small amounts of hydrochloric acid or sodium hydroxide may be added during manufacturing to fine-tune the pH.
Notably, Wegovy contains no preservatives like phenol or metacresol, which are common in multi-dose insulin pens. Each Wegovy pen is designed for a single use and should be discarded after injection.
How Wegovy Compares to Ozempic
Wegovy and Ozempic contain the same active ingredient, semaglutide, with the same chemical structure. The difference is dosing and approved use. Wegovy’s maximum dose is 2.4 mg per week, prescribed for weight management. Ozempic tops out at 2 mg per week and is approved for type 2 diabetes. The inactive ingredients in the injectable formulations are essentially the same.
How Semaglutide Works in Your Body
Once injected, semaglutide activates GLP-1 receptors in several parts of the body. In the brain, it acts on appetite-regulating areas of the hypothalamus, boosting signals that make you feel full while dialing down signals that drive hunger. It also influences a brain region involved in reward processing, which can reduce the pleasurable pull of food and make it easier to eat less without feeling deprived.
In the gut, semaglutide slows the rate at which your stomach empties after a meal. This means food stays in your stomach longer, contributing to that feeling of fullness. Together, these central and peripheral effects lead to reduced calorie intake, which drives the weight loss seen in clinical trials.
Storage and Stability
Because Wegovy is a protein-based medication in a preservative-free solution, storage matters. Keep unused pens refrigerated between 36°F and 46°F (2°C to 8°C) in their original cartons. If needed, a pen can be stored at room temperature, up to 86°F (30°C), for a maximum of 28 days before use. Discard any pen that has been frozen, exposed to direct light, left above 86°F, or kept out of the refrigerator for longer than 28 days.