Introduction: Phenazepam therapy can often be ineffective and some patients develop dose-related adverse drug reactions. Aim. The purpose of this research was to study the effect of the CYP2C19*2 (681G>A, rs4244285) in patients with anxiety disorders and alcohol dependence taking phenazepam therapy. Materials & methods: Patients (175 males, average age: 37.16 ± 7.84 years) received phenazepam in tablet form for 5 days. Genotyping was performed by real-Time polymerase chain reaction. Results: The statistically significant differences in the UKU Side-Effect Rating Scale scores on the fifth day of therapy: (CYP2C19*1/*1) 2.00 [1.00; 2.00), (CYP2C19*1/*2) 7.00 (7.00; 7.00), (CYP2C19*2/*2) 9.00 (8.00; 9.00), p < 0.001. Conclusion: This study demonstrated the different efficacy and safety of phenazepam in patients with different genotypes of CYP2C19*2.