Non-Ulcer Dyspepsia and some cases of nausea and vomiting
In patients with chronic dyspepsia who do not have ulcer disease, the role of H.pylori therapy has not been proven. Therefore, consider other diagnoses before assuming that H.pylori is the cause. If other diagnoses are not obvious, consider a trial of anti-H.pylori therapy. In some patients an immediate response is seen but in others gradual improvement occurs over several months.
There are several reports indicating that patients with chronic vomiting remit after H.pylori is eradicated. Try antibiotics if a patient known to have H. pylori has nausea. Start treatment gradually with the least toxic combination first. For example, omeprazole....then amoxicillin...then metronidazole or clarithromycin as the patient settles (this may be a week or two).
If the patient has not been investigated before, but has symptoms compatible with peptic ulcer, testing for and treating H.pylori is probably safe and cost effective.