The study aimed to compare two treatment services, primary services (GPs) and mental health services (psychiatrists), in their approach to treating patients with dual diagnosis. Data was retrieved through a postal questionnaire to 200 Dublin-based GPs and 200 psychiatrists. Results showed that, in practice, GPs were less likely than psychiatrists to have a treatment model for dual diagnosis in a patient. GPs also tended to treat patients with dual diagnosis as if they had two separate conditions. This thesis concludes that reluctance to accept patients with dual diagnosis is due to a lack of mental health training. This reluctance could account for the high percentage of readmissions for patients with dual diagnosis. The author concludes that there is a divide between primary and mental health care services which is to the detriment of the patient. Recommendations include more mental health training and awareness for GP's, especially regarding dual diagnosis. Also, to emphasisise aspects of mental health within in-service training progammes for addction services employees. The author also recommends incorporating a shared care treatment model to be adapted by all service providers.