Aim of the study:
The present study aimed at determining the effectiveness of Acceptance and Commitment Therapy (ACT) on addiction severity of methamphetamine users.

Subject or material and methods:
To achieve research goals and to test the hypotheses, theoretical bases and background of the study were investigated, showing that ACT decreased addiction severity of methamphetamine users. After visiting outpatient centers in Tehran and screening the visitors, 48 subjects were selected as initial sample. After removal of those who were unwilling to cooperate with the researcher, the remaining 30 subjects were assigned randomly to ACT or waiting-list control (WLC) condition. Treatment intervention was administered individually over 12 sessions of 45-60 minutes weekly. Data was analyzed using multivariate analysis of covariance.

Results:
Results showed that ACT reduced addiction severity of methamphetamine users in seven dimensions of medical condition (p=0.016), occupational status (p=0.037), alcohol use status (p=0.002), substance use status (p=0.001), legal status (p=0.002), family status (p=0.000), and psychological condition (p=0.000).

Discussion:
Enhancing psychological flexibility through redirecting the experiential avoidance to experiential acceptance and clarifying the values, the seven dimensions of addiction severity were improved.

Conclusions:
The findings suggest the effect of ACT on reduction of the severity addiction of methamphetamine users.