Acid reflux occurs when stomach acid frequently flows back into the tube connecting your mouth and stomach (esophagus). This backwash (acid reflux) can irritate the lining of your esophagus. Many people experience acid reflux from time to time. Acid reflux happens to nearly everyone at some point in their life. Having acid reflux and heartburn now and then is totally normal but if you have acid reflux (heartburn) more than twice a week, you may need daily medications to manage your condition.

Omeprazole takes about 1 hour to block the production of stomach acid and it’s maximal effect occurs around 2 hours after beginning therapy. The action of omeprazole can continue for about 3 days. Omeprazole must continue to be taken on a daily basis for the stomach acid to remain low. If Omeprazole is only taken on an “as needed” basis, you will most likely experience breakthrough acid reflux. 
As with any prescription medication you may experience side effects while taking omeprazole. Commonly reported side effects can include headache, stomach pain, and nausea.