Which is associated with more/less possible adverse health effects from long term use? prilosec or pepcid (famotidine)?

Heartburn meds : Both PPI's, such as Prilosec, and H2-blockers, such as Pepcid, (famotidine) are frequently used medications for Gerd. Both of these classes of medicines are reasonably safe, and if needed can be used long-term generally very safely. If you have severe symptoms, I would not shy away from using whichever controls your symptoms the best. Be sure to follow anti-reflux precautions! Good luck.