Effect of Regular Naltrexone Dosing on Disordered Gamblers

Eligibility Details: Inclusion Criteria: - 18-70 years of age. - Provide written consent. - Evidence of Disordered Gambling (DSM-V; American Psychiatric Association, 2013) - Seeking treatment for disordered gambling, referrals, or responding to information about the study presented in the media. - Primarily Video Lottery Terminal gamblers (to standardize gamblers and as we are using stimuli in the gambling stimuli task that is similar to video lottery terminals displays so gamblers will be familiar with these images). - Attendance at Alberta Health Service Evening Gambling Intensive Program (EGRIP) or similar - English speaking Exclusion Criteria: - Evidence of a current significant medical illness, or unmanaged psychiatric or neurological disorder. - Positive urine specimen to drugs of abuse. - History of a traumatic brain injury or loss of consciousness (10 minutes or more). - History of evidence of claustrophobia - Left handed. - Any condition or circumstance that prohibit imaging sessions such as metal implants. - Contraindications to clinical doses of naltrexone. - History or evidence of allergic reactions to naltrexone administration (i.e., rash, itching/swelling, severe dizziness, or trouble breathing). - Concurrent use of additional alcohol dependence medication e.g. disulfiram. - Evidence of current illicit opioid use - Use of medications containing opioids/opiates - Uncorrected visual impairment - Evidence of brain abnormalities from structural scans - Evidence of heart, liver or kidney failure. - Failure to attend weekly EGRIP counselling sessions or similar - Pregnant Other Requirements: - If sexually active must use contraception - Cannot make ovum or sperm donation during study and six-months thereafter