Prilosec presciptions contains either 10 mg, 20 mg or 40 mg of omeprazole. The OTC are sold in 20mg. One could double the OTC does to take the 40mg does if needed. If using prilosec, i certainly would buy it OTC if it saved me money over a prescription.
If you have prescription coverage you might want to try the generic (omeprozloe) I used 20mg twice daily. With my insurance I got 60 pills per month & even with a copay it was still far less $ than anything OTC.