The FDA has issued a warning about long-term use of proton-pump inhibitors (PPI) like Nexium, Dexilant, Prilosec, Zegerid, Prevacid, Protonix, Aciphex, and Vimovo. They are acid reducers used primarily by people with acid reflux and/or heartburn: Link to warning

Here is the site that first alerted me to this, and also has a lot of info on how to solve acid reflux and/or heartburn without resorting to drugs: Link to Healthy Skeptic site