Rabeprazole is a proton pump inhibitor sold (as its sodium salt) under the brand name Aciphex and Pariet (distributed by Janssen-Ortho).
It is used in the treatment of gastric ulcers and GERD (or heartburn). It is taken once/day along with a full glass of water (preferable 30 min before breakfast). The duration of treatment is usually 4 weeks but could be longer if the symptoms persist.
Sometimes, one may start feeling better after a few days but it is essential to complete the full course of treatment.