Prescription pepcid causes constipation. Well i feel wonderful from taking it because with my gastritis, GERD and nausea it was really hard to continue my everyday life. After 3 weeks of taking it i have to say i don't have any symptoms and i can finally eat but i'm very constiapted and i know it's a side effect of the medication. What can i... show more Well i feel wonderful from taking it because with my gastritis, GERD and nausea it was really hard to continue my everyday life.