5 Answers - Posted in: prilosec - Answer: hi there prilosec i've been on it for several years so i guess if you can My question is can I use Prilosec OTC for longer than the 14 days the package says. Last summer I developed . I would like to find out about side effects of long term usage of omerprazole. Learn about the potential side effects of Prilosec OTC (omeprazole). Includes Along with its needed effects, omeprazole (the active ingredient contained in Prilosec OTC) may cause some unwanted effects.