Comorbid substance abuse leads to many deleterious effects such as medical comorbidities and nonadherence, which is one of the most problematic issues. People with schizophrenia and substance use disorders (SUDs) are at an increased risk nonadherence compared to those who do not use alcohol and illicit drugs. The investigators propose that this new marketed injectable antipsychotic with many benefits over other available long acting injectable agents would be beneficial in the dually diagnosed population and may represent a specific schizophrenia subpopulation where long acting agents may be considered an important therapeutic option.

Inclusion Criteria:

• Be between ages 18 and 64
• Either gender
• Any race
• Meet DSM-IV-TR criteria for Schizophrenia or Schizoaffective Disorder.
• Alcohol and/or cannabis use defined as a DSM-IV diagnosis abuse, dependence or regular use defined as 3 times per week during the past year
• Agree to take or use birth control during the study.

Exclusion Criteria:

• Previous lack of response or serious adverse event to risperidone or paliperidone.
• Currently on a long acting injectable antipsychotic.
• A score of less than 10 on the Evaluation to Sign Consent (ESC).
• Medical illnesses, which may compromise safe study participation.
• Pregnant and lactating females.
• QTc interval > 450 milliseconds males or > 470 milliseconds in females
• Currently on acamprosate, naltrexone and disulfiram.