This is an open-labeled, 3-phase, self-control study. In phase 1, blood is sampled from volunteers who will take placebo to obtain the baseline value. In phase 2, volunteers will take a single oral dose of 2000 mg GABA. There are at least 7 days between the two phases. In phase 3, volunteers will take a repeated oral dose of 2000 mg GABA (thrice daily for seven days). There are at least 5-7 days between phase 3 and phase 3. In each phase, individuals will be observed for 24 hours to obtain the complete concentration time curve. 4 ml of blood will be sampled at the following time-point for predose and 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, 6, 8, 10, 12 and 24 hour postdose.