Until positive results were found with oral naltrexone, no medication has been effective against amphetamine dependence. The primary aim of this pilot study is to replicate the findings of the Swedish team that showed oral Naltrexone prevented relapse to amphetamine addiction and to extend their results by randomizing treatment-seeking amphetamine addicted patients to a 6 month course of VIVITROL (naltrexone for extended-release injectable suspension) or VIVITROL placebo. Patients in each group will receive drug counseling. VIVITROL is administered monthly and may be a better test of efficacy than tablets that must be taken daily.

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