mopurist

Prilosec OTC (and all of the proton pump inhibitors) are easily destroyed
in a highly acidic environment like the stomach. That is why they all use
some form of delayed-release mechanism or buffer.

Prilosec OTC uses a coating on the tablet to achieve delayed release. By
breaking the tablets you are essentially creating an immediate release
formulation. Much of the drug will be rendered ineffective in the stomach
due to the exposure to a low pH environment (stomach acid). That is the
reason that the package states not to break the tablets.

Some of it may survive, but the resulting dose will be smaller than the
10mg you were expecting. How much smaller depends upon alot of factors,
including the pH of the stomach at the time it is taken, rate of the
tablets movement through the stomach, how much of the coating was
removed, etc.