Background: Substance abuse in various parts of the globe appears to be evolving in different patterns and this keeps threatening the physical as well as socioeconomic well-being of homes, societies and countries. Aim: This study investigated the pattern of substance use among patients on drug treatment at the University of Port Harcourt Teaching Hospital. Methodology: NENDU data from the Drug Unit from January 2018 to February 2020 were investigated after ethical clearance in this descriptive retrospective study. Data analysis was performed using the Statistical Package for Social Sciences (SPSS) software version 20. Results: Results revealed that out of a total of 104 registered patients, cannabis was the most declared drug with 42.3% use. Cannabis was also the most frequently used drug (28 persons used it daily) followed by alcohol (8 persons used it daily). Street dealers constituted the readiest source with 96 (92.3%) while poly-drug was higher with 76 (73.1%). The majority of respondents using substances/drugs were males 98 (94.2%), singles 93 (89.4%), and college degree holders 73 (75.0%). Conclusion: From the conclusion of this study, there are emerging varied patterns of substance use. Hence, there is a need for increased sensitization and health education programs to curb the trend.