Another alternative to cutting back to half dose (if that doesn't work) is to cut the dose or frequency, and substitute an H2 inhibitor such as Zantac (ranitidine) or Pepcid, which are a different class of drug without the same long term side effect concerns as the PPI's, but also somewhat less effective or enduring. But they work well in cutting back the PPI therapy.
If one is taking omeprazole twice a day, substitute one of those doses with Zantac, or take a half dose of omeprazole in the morning and a dose of Zantac in the evening. Then try going to all zantac after a couple of weeks, etc.