The screening phase is intended for diagnosing and assessing the patient for possible inclusion in the study and for providing an adequate washout period.~At the first stage, a number of 69 subjects will be randomly assigned on a 1:1:1 basis to one of the three arms (1 PDC-1421 Capsule plus 1 placebo TID, 2 PDC-1421 Capsules TID, 2 placebo TID) for 8 weeks and evaluated the safety and efficacy every two weeks during the treatment period. An interim analysis will be conducted to evaluate the efficacy of PDC-1421 and to decide whether it is necessary to enter the second stage of the Part II study in which 30 subjects will be randomly assigned on a 1:1:1 basis to one of the three treatment arms and receive the same treatment.~Simple descriptive statistics with a 95% confidence interval will be performed with data collected in this study wherever applicable. The safety and efficacy data will be analyzed using the non-parametric method wherever appropriate.~The primary endpoint will be analyzed by chi-square test, while the secondary endpoints will be analyzed using the ANOVA or Kruskal-Wallis non-parametric ANOVA test for continuous endpoints and chi-square test for binary endpoints.
Part II is a double-blind, randomized, parallel-group, placebo-controlled study. The primary objective of this trial is to determine the effective doses and treatment period of PDC-1421 Capsule in subjects with ADHD. The secondary objective is to evaluate the safety of PDC-1421 Capsule in subjects receiving PDC-1421 at various dose levels.