Omeprazole contains a single active ingredient, also called omeprazole, that belongs to a class of drugs known as proton pump inhibitors. But the full ingredient list goes well beyond that one compound. The capsules or tablets you swallow are carefully engineered with a dozen or more inactive ingredients that protect the drug, help it dissolve in the right place, and hold everything together. What exactly those inactive ingredients are depends on whether you’re taking the brand name (Prilosec), the OTC version, or a generic.
The Active Ingredient
The active ingredient is omeprazole itself, a chemical compound with the molecular formula C17H19N3O3S. It works by shutting down the tiny acid pumps lining your stomach wall. These pumps (called proton pumps) are what push hydrochloric acid into your stomach. Omeprazole binds to them and blocks their activity, which dramatically reduces acid production. This is why it’s used for heartburn, acid reflux, and stomach ulcers.
The drug was first approved in the United States on September 14, 1989, and it’s now available both by prescription (in 10 mg, 20 mg, and 40 mg capsules) and over the counter (typically 20 mg tablets). The OTC version uses a slightly different form called omeprazole magnesium, which is just the drug bonded to magnesium to improve stability.
Why the Coating Matters
Omeprazole has an unusual problem: stomach acid destroys it. In acidic conditions at pH 5.0, the drug breaks down to half its strength in just 43 minutes. In alkaline conditions, by contrast, it can remain stable for months. This means if you swallowed plain omeprazole powder, your own stomach acid would degrade much of it before it could be absorbed.
To solve this, every omeprazole product uses a delayed-release design. The drug is either packed into enteric-coated granules inside a capsule or pressed into a tablet with a protective coating. These coatings resist acid but dissolve once the drug reaches the more alkaline environment of your small intestine. The coating materials typically include compounds like hypromellose (a cellulose derivative) and sometimes specific polymers designed to dissolve only above a certain pH.
Inactive Ingredients in Prilosec OTC
The OTC tablet form of Prilosec contains a long list of inactive ingredients, each serving a specific purpose:
- Rice starch and microcrystalline cellulose: fillers that give the tablet its bulk and structure
- Hypromellose and hydroxypropyl cellulose: coating agents that control how and where the tablet dissolves
- Magnesium stearate and sodium stearyl fumarate: lubricants that prevent the tablet from sticking to manufacturing equipment
- Sucrose: a sugar used as a stabilizer for the enteric-coated layer
- Polyethylene glycol 6000 and triethyl citrate: plasticizers that keep the coating flexible so it doesn’t crack
- Titanium dioxide and red iron oxide: colorants that give the tablet its appearance
- Talc and paraffin: anti-caking and smoothing agents
- Polysorbate 80 and glyceryl monostearate: emulsifiers that help blend ingredients evenly
- Povidone K60: a binder that holds the tablet together
Inactive Ingredients in Prescription Capsules
Prescription Prilosec capsules have a different makeup. The granules inside contain cellulose, disodium hydrogen phosphate, hydroxypropyl cellulose, hypromellose, lactose, mannitol, and sodium lauryl sulfate. The capsule shells themselves are made from gelatin and colored with various dyes including FD&C Blue #1, FD&C Red #40, D&C Red #28, and titanium dioxide. The 10 mg and 40 mg capsules also contain D&C Yellow #10.
Generic versions vary by manufacturer but use similar categories of ingredients. Some store-brand formulations, for example, include lactose monohydrate, carnauba wax, sodium starch glycolate, and propylene glycol alongside the standard coating and coloring agents.
Allergens and Dietary Concerns
If you have dietary restrictions or allergies, a few ingredients are worth noting. Prescription capsule formulations often contain lactose as a filler, and some generic tablets do as well. If you’re lactose intolerant, the small amount in a single dose is unlikely to cause symptoms, but it’s worth checking the specific product label.
The capsule shells on prescription versions contain gelatin, which is animal-derived. This matters if you follow a vegetarian or vegan diet. The OTC tablet form of Prilosec does not use a gelatin capsule, making it a potential alternative, though you should confirm with the packaging since formulations can change.
Several formulations include artificial dyes like FD&C Red #40, FD&C Blue #1, and FD&C Yellow #6. People with sensitivities to these dyes can look for versions with fewer colorants. The 20 mg prescription capsule, for instance, uses only FD&C Blue #1, while the 10 mg and 40 mg capsules contain additional dyes. Sodium lauryl sulfate, a common detergent used to help the drug dissolve, appears in both prescription and OTC versions and occasionally causes irritation in sensitive individuals.
None of the standard omeprazole formulations list gluten-containing ingredients, but pharmaceutical products are not required to carry gluten-free certification. If you have celiac disease, contacting the specific manufacturer is the most reliable way to confirm.