Will taking 40mg of omeprazole give you nausea? how long does it take at that dose to leave the body?

Omeprazole: Omeprazole blocks acid secretion by the stomach but nausea would be a most unusual side effect in my long experience prescribing it. Generally a dose is prescribed for once daily consistent with a 24 hour effect. In your case, if this reaction occurs every time you take it, it is a bone fide side effect. Your pharmacist may have more information about this matter. Zantac may be better tolerated.