Substance abuse has been reported in association with various medical conditions. Research has shown a considerable tobacco and opium dependence with the rate of 44.2% and 5.8% for heart diseases and 17.9% and 7.1% for pulmonary diseases, respectively (
11). This phenomenon has been reported in many other medical diseases, including rheumatologic diseases (
12) and hemophilia (
13).
In our study, the rate of substance abuse in the psychiatric inpatients was higher than the rate of this co-morbidity that has been reported in the literature in association with any other medical condition. This may be due to the nature of psychiatric problems and therefore needs more attention during the treatment process (
14).
Although we found an association of substance dependence with two groups of psychiatric disorders, only in one of these, i.e. schizophrenia, the association was statistically significant and in the second group (other psychiatric disorders, containing a large number of non-specific psychiatric disorders), it was not.
In our study the smoking rate was approximately three times higher than what has been reported in the general population (
15). Smoking in psychiatric patients increases the activity of P450 system in the liver and CYP1A2 enzymes, thus decreases the blood concentration of many antipsychotic drugs and their side effects, which might be rewarding for the patients (
16). Our study also found a strong relationship between smoking and substance abuse event prior to the onset of psychiatric disorders.
There are many differences in the type of substance abuse or dependence and specific psychiatric disorders and their association in the literature. Studies have shown a different pattern of substance abuse or dependence in Iran compared to the rest of the world. These differences are partly cultural and partly due to the availability of substances in this part of the world. For example, raw opium dependence is quite common because Iran is a neighbor to Afghanistan which is the main producer of this substance in the world (
17). Opioids are the primary drugs of abuse in Iran. Two different forms of opioid abuse afflict Iran; heroin injection and opium smoking and ingestion (
18). Indigenous raw opium accounts for 69% to 94.6% of total opioid use in this country (
16). Cannabinoid substances are the second prevalent drugs of abuse in Iran (
19).
There are a number of reasons why patients with dual diagnosis do not receive the necessary care. These reasons include lack of treatment access, high cost of treatment, stigmatization, treating only mental illness or substance use disorders in separation, as well as a medical care system that do not put enough emphasis on the recognition or treatment of a co-morbid substance misuse and also a medical education system that dedicate very little training or teaching time to this significant area of clinical practice (
7).
The results of our study revealed a high prevalence of co-morbid substance misuse in psychiatric inpatients, which has a significant impact on the management of both conditions. In this respect, we recommend that the protocol for the management of psychiatric illnesses in psychiatric hospitals be revised so that the early recognition and management of co-morbid substance misuse are more emphasized.
In addition, a strong association of smoking and substance misuse has been noted in our study. This association with high rate of substance misuse warrants further studies on how public education about harmful effect of cigarette smoking can help reduce the overall rate of substance dependency in the general population.