How to use Prilosec OTC. Read the Patient Information Leaflet if available from your pharmacist before you start taking omeprazole and each time you get a refill. What are the long-term side effects of taking acid reflux medications (Prevacid, Prilosec, Aciphex, etc.)? Prilosec, and the generic version, provide 100% relief of symptoms within 1-3 days of taking the first dose. In my case, within 1 day of taking it I immediately felt better and now feel normal each day. I've not had a single episode of acid reflex since I began taking it daily. Our Prilosec Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication. This is not a complete list of side effects and others may occur. I have been taking Omeprazole, the SAME as Prilosec, for over 12 YEARS. It stops ALL of my acid reflux, and I have had NO SIDE EFFECTS!!! I buy a 1 year supply on Ebay for about $35 from a US Seller with free shipping. Why ANYONE would buy Prilosec for what they charge is beyond me. But, I can tell you that Omeprazole works, and it is CHEAP!!! Prilosec (omeprazole) is used to treat symptoms of GERD and other conditions caused by excess stomach acid. Includes Prilosec side effects, interactions and indications. Includes Prilosec side effects, interactions and indications. According to medical references, flatulence (excessive gas) and constipation are possible side effects reported by studied patients taking Prilosec. The incidence that flatulence was reported at. Side effects from omeprazole: Taking omeprazole with certain medications raises your risk of side effects from omeprazole. This is because the amount of omeprazole in your body is increased. I have been taking 20 mg of Prilosec every day for about one year now. I guess my heartburn is okay if I watch what I eat, but that is my problem. The information is not intended to cover all possible uses, directions, precautions, drug interactions or adverse effects, nor should it be construed to indicate that use of a particular drug is.