Background: Methamphetamine (MA) is one of the most common drugs of abuse in Thailand. MA use may cause neurotoxicity, immune-inflammatory and oxidative stress responses and, consequently, MA-induced psychosis (MIP).Aims: This study aims to examine the effects of MA use and dependence and MA withdrawal symptoms on the telomere to single copy gene (T/S) ratio and whether shortening of the latter is associated with MIP.Methods: This study included 185 MA-abuse, 118 MA-dependent, and 67 MIP patients, diagnosed using DSM-IV-TR criteria. The Semi-structured Assessment for Drug Dependence and Alcoholism (SSADDA) questionnaire was employed to collect clinical and MA-related data. MIP was confirmed using the Methamphetamine Experience Questionnaire (MEQ). The leukocyte telomere length was measured in all participants using real-time polymerase chain reaction measuring the Telomere/Single gene ratio (T/S ratio). Results: There were no significant associations between the T/S ratio and severity of MA-use, MIP, MA withdrawal symptoms including depression and psychomotor retardation. MIP was significantly predicted by alcohol dependence, antisocial personality disorder, and MA-use severity. There were significant and positive associations between the T/S ratio and previous traumatic events and life-threatening accidents. The T/S ratio was not affected by comorbid alcohol and nicotine dependence. Alcohol and nicotine dependence, antisocial personality, and severity of MA use increased risk of MA withdrawal symptoms. Conclusion: MIP and MA-use severity do not affect leukocyte telomere length, but telomere length may be affected by previous traumatic events and life-threatening accidents.