 This is a randomized study drug assigned by chance, sequential-cohort time lagged, double-blind neither the participant or the study doctor will know the name of the assigned treatment, parallel-group, placebo-controlled, 3-arm participants will be assigned to 1 of 3 treatment groups, single-center, Phase 1 study of multiple ascending doses of tramadol HCl in healthy adult volunteers. Thirty participants 15 men and 15 women will be sequentially assigned to 1 of 3 treatment groups of 10 subjects each 5 men and 5 women. Participants in each treatment group will receive a total of 9 oral doses one every 6 hours of tramadol HCl or placebo, in the ratio of 4:1. The study includes a screening phase and a double-blind treatment phase. The treatment phase will consist of 3 treatment periods separated by a 5-day safety review period before the next ascending dose of study drug is administered to the next group. Participants in each group will be confined to the study center for a total of 5 days, the total duration of each subjects participation will be up to 33 days, including the screening phase. The total duration of the study completion of all 3 treatment cohorts will be up-to-approximately 2 months. 