**3. Clinical study**

The study involves opiate-dependent individuals who consented, met our study criteria and were invited to participate in the study. The study involved them taking prescribed doses of daily methadone according to Methadone Maintenance Therapy (MMT) guidelines prepared by the Malaysian Ministry of Health and be monitored regularly based on our study protocols. They were followed up for 12 months during the study period. At follow up, 5 ml of venous blood were drawn for the determination plasma methadone level using in-house methadone ELISA kit.

However, at 12th month follow up, 88 out of the 128 participants fail to meet the inclusion criteria. Thus, in order to assess the efficacy of low dose methadone on the withdrawal effect and sleeping quality, a subset of only 40 patients was further selected to participate. They were given a fixed 40 mg daily dose of methadone. Their withdrawal score and sleeping quality were assessed during the fourth week of the study.
