Objective: Impulsive, neurotic, problematic, and outward personality traits are risk factors for the development of substance use disorders. The purpose of this study is to investigate whether the chronobiologic type of eveningness which shows high-neuroticism, low self-control and escape from harm is a risk factor for the development of substance use disorders in heroin dependents more often than healthy controls.

Material and Method: After the approval of the local ethics committee, Sociodemographic and Clinical Data Form including age, gender, marital status, education level and the Morningness-Eveningness Questionnaire (MEQ) were applied to all cases. Two groups were taken in to the study; heroin dependent group (Group 1) and control group (Group 2).

Results: There was no significant difference in age between dependent group and control group. No significant difference was found between the dependent group and the control group in the MEQ score. There was also no significant difference between categorized MEQ classes. However, the definite morningness and definite eveningness types were never seen in the dependent group.

Conclusion: In this study, we found no significant difference between the heroin-dependent group and the control group in terms of morningness-eveningness. Our study can be considered as a preliminary study in this regard and the literature can be contributed by using wider series with new studies on larger samples.