Extended Release Naltrexone for Treating Amphetamine Dependence in Iceland

Inclusion Criteria: 1. Age 18 or above; 2. Diagnosis of amphetamine dependence as defined by DSM-IV-TR with 10 or more days of amphetamine use in the past month, and patient and clinician identify amphetamine dependence as the main problem; 3. Abstinent from substances (alcohol, amphetamines, cannabinoid, cocaine, hallucinogens, opioids, benzodiazepines \[unless used to treat alcohol withdrawal\] for at least 7 days prior to receiving study drug or placebo; 4. Provision of telephone numbers/contacts of three or more people that are likely to know where can be located if unable to be contacted directly; 5. Successfully complete 7-10 day assessment and study baseline measures at Vogur Exclusion Criteria: 1. Any liver test \>5 times the top limit of normal; Physiologically dependent on opioids or other substances (nicotine excepted) at time of admission to Vogur; 2. Suspected or known concomitant use of opioid analgesics, positive opioid urine drug test or positive naloxone challenge: 3. Schizophrenia, Bipolar I or other non-substance related psychotic disorder; Severely depressed, suicidal or homicidal: Dementia: Inability to understand the informed consent; 4. Planning to move from the Reykjavík area or enter jail within the next 12 months; 5. Likely to receive opioid analgesics in next 6 months associated with possible or scheduled surgery or procedure; 6. Known hypersensitivity to naltrexone, polyactide-co-glycolide (PLG); carboxymethylcellulose, or any other component of the diluent; 7. Female subjects who are pregnant or lactating, or of child bearing potential who are not using acceptable methods of birth control; 8. A body habitus that precludes use of the customized needle for intramuscular injection, based on clinical judgment; 9. Use of an investigational agent in the past 30 days