Prilosec OTC is clinically proven to block heartburn for 24 hours. And that means with 1 pill a day for 14 days, you get relief from frequent heartburn.  While taking Prilosec OTC, heartburn won't keep coming back. It’s possible with Prilosec OTC. Use as directed for 14 days to treat frequent heartburn. Do not take for more than 14 days or more often than every 4 months unless directed by a doctor. May take 1 to 4 days for full effect. Not for immediate relief. One pill a day. 24 Hours. Zero Heartburn. Directly blocks many of the active stomach pumps that produce acid before they start. Works for 24 hours with one pill a day. It is indicated for a 14-day course of treatment, up to three times a year.