The COVID-19 pandemic had profound impacts worldwide on individuals with mental and behavioral disorders, including disorders due to psychoactive substance use. We investigated how the COVID-19 pandemic affected the trends in these disorders in the Republic of Kazakhstan. We researched and compared ICD-10 data on mental and behavioral disorders due to substance use in Kazakhstan that were diagnosed in 2018-2019 (pre-pandemic) versus 2020-2021 (the pandemic period). The data for the pandemic period were significantly different from those of the pre-pandemic in that (i) 'other stimulant-related disorders (F15)' and 'other psychoactive substance-related disorders (F19)' were increased in the younger age groups, (ii) the risk of 'opioid-related disorders (F11)' was decreased in the 30-year-old group in both males and females, and (iii) the risk of 'alcohol-related disorders (F10)' was increased in the 30-year-old group and decreased in the 20- and 50-year-old groups. In only the males, (iv) the risk of 'other psychoactive substance-related disorders (F19)' was increased in almost all of the age groups, and (v) the risk of 'cannabis-related disorders (F12)' was increased in the ≥50-year-olds. The pre-pandemic and pandemic periods thus involved changes due to COVID-19 in both males and females that were especially notable in males. These results indicate that further measures designed to prevent mental and behavioral disorders due to psychoactive substances are necessary at the primary, secondary, and tertiary levels, and personnel in medicine/nursing, the government, private organizations, and the public need to collaborate to devise such measures.