The use of illicit and licit substances has increased worldwide with important health and social consequences including the loss of people productive years and their lives [1].

According to the United Nations Office on Drug and Crime it is estimated that 243 million people aged 15–64 worldwide are users of some illicit drug, resulting in approximately 5,000 drug-related deaths per annum in Latin America and Caribbean [1].

In Brazil, data from the II the Brazilian National Alcohol and Drugs Survey indicated a prevalence of approximately 4% of marijuana use among adolescents and there are reports of increasing dependence among cannabis users [2]. With regard to cocaine and crack, 1.7% of Brazilians have used intranasal cocaine and approximately 0.8% reported smoking cocaine in the form of crack [3,4]. The prevalence of intravenous drug use in Brazil was considered very low [3,4].

Alcohol is seen by many as a more socially acceptable drug and one that has been widely used in many cultures for centuries. However, it is known that alcohol causes a large range of diseases, in addition to creating social and economic burdens on societies [4]. Various factors are associated with alcohol consumption and alcohol-related harm such as economic development, culture, availability of alcohol and the level and effectiveness of alcohol policies [4-6].

It is estimated that in Brazil there is a consumption of about 8.7 liters of pure alcohol per capita by people over the age of 15 years, and 25 percent of adults (approximately 32 million people) have some type of alcohol-related disorder [4,7]. Some national policies try to impact on alcohol consumption, such as the national legal minimum age of 18 for on-premise sale of alcoholic beverages, legally binding regulations on alcohol advertising and a national maximum legal blood alcohol concentration when driving a vehicle [4]. However, alcohol consumption continues to cause liver cirrhosis, road traffic accidents, dependence, and other social problems in Brazilian citizens [4-6].

As previously mentioned, drug and alcohol use and abuse causes great social and a financial loss to the country, including crime, domestic violence, child abuse, lost productivity, family disintegration and high risk of diseases such as HIV, Hepatitis, Tuberculosis, Cirrhosis [4-7]. Their use is influenced by gender, socioeconomic status, relationships with family and friends, culture and context [4,8,9].

Alcohol and drug addiction can have important impacts on the oral health [8-10] of these individuals. Subjects who are alcohol and drug dependent are at increased risk of having oral health compromised for various reasons, such as limited access to dental care, poor diet, poor oral hygiene habits, lack of care of oral health and general health. Furthermore, there are the effects of the substances themselves on the teeth and oral mucosa leading to bruxism, tooth loss, periodontal disease, halitosis, stomatitis and oral cancer [10-18].

Studies have shown that addiction affects the quality of life of substance users [19-25]. However, very little is known about the impact of oral health conditions on general quality of life of individuals who become addicted to alcohol and/or drugs [26].

The objective of the present study was to investigate the impact of oral health conditions, socioeconomic status and use of specific substances on the quality of life of addicted persons receiving care at?/who frequent outpatient clinics in Brazil.

Considering the 286 volunteers drawn initially, 24 did not agree to participate in the survey; therefore 8% was its rate of abstention, thereby arriving at a final sample of 262 subjects.

Of the subjects 17.9% (n = 47) were observed to report 1 or less minimum wages as their monthly family income. With respect to education, the majority of the volunteers (61.1%), parents (64.1%) and mothers (79.4%) had up to 8 years of schooling. With respect to substance use, 80.9%, 46.56% and 60.3% of the sample were classified by ASSIST as having moderate/high risk of being alcohol, marijuana and cocaine/crack users.

Quality of life (QoL) is a multidimentional construct with interrelated domains such as physical, social, psychological and the living environment [32]. According to the World Health Organization, QoL is defined as “an individual’s perception of his/her position in life in the context of the culture and value systems in which he/she lives, and in relation to their goals, expectations, standards and concerns” [33]. Thus, QoL is influenced by sociocultural, economic, psychological and physical factors, transcending the normative vision of well-being of the biomedical model of health.

The WHOQoL-Bref has been used as generic instrument to measure quality of life without a specific correlation with any particular disease. Moreover, it comprises the satisfaction of individual with life in general, covering different domains than other health-related quality of life instruments, and it has been widely used in the area of substance use [34-36].

Drug and alcohol users have generally been found to have lower QoL than do individuals in the general population [35-37]. However, as observed in our study, the impact of addiction on QoL was also mediated by the sociodemographic conditions of users, in a trend similar to that observed in populations of non-dependent alcohol and drug users [19-37]. This is because drug users treated at CAPS-AD, who had a family income of less than or equal to one minimum wage were 2.41 times more likely to be associated with low quality of life than those from families with higher incomes. This datum was also observed in the study Moreira et al. [37], in which the authors reported that drug users, earning less than five minimum salaries, were three times more likely to have a worse quality of life compared with those with higher incomes. Therefore, the extent to which substance abuse affects QoL is affected by social determinants of health.

Despite the growing trend in studies evaluating the quality of life of drug and alcohol users [19,20,38,39], additional research investigating the associations of QOL with other classes of drugs as such marijuana are needed. In the present study, we observed that moderate and high-level users of cocaine and crack have 2.2 times more chance of presenting a worse general quality of life than low-level users and this was the only substance dependence that demonstrated significant associations with the overall scores of WHOQOL-Bref.

According to the literature, alcohol and marijuana may be less harmful to health in comparison with cocaine and crack cocaine. The latter two can cause more psychiatric comorbidities and cognitive impairment, and are also associated with sexually transmitted diseases and involvement in illegal activities, factors that can impact on health-related quality of life [1,2,40,41].

There is a scarcity of investigation into the impact of oral health on quality of life among drug and alcohol users in the literature. Wijk et al. [26] evaluated the impact of oral health on the daily functioning of a group of individuals addicted to alcohol and/or drugs, who were being treated at a specialized dentistry center in Amsterdam, and observed that the poor oral health had a substantial impact on their daily functioning. However, the authors used the short version of Oral Health Impact Profile questionnaire (OHIP-14), a specific oral health-related quality of life instrument developed to evaluate the functional and psychosocial impacts of oral diseases. Therefore, in our view, this is the first study to investigate the impact of caries experience on general quality of life by means of the WHOQOL-Brief instrument. There is an instrument to assess quality of life in drug users, but it was not validated in Brazil yet (Drug User Quality of Life Scale: DUQOL) [24]. We verified that caries experience affected the QoL of addicted persons, which led us to reflecting on the importance of the dentist as a relevant professional in the multidisciplinary teams that take care of addictive users. Dentists would help to promote oral and general health of these individuals, and contribute to their psychosocial rehabilitation, by assisting them to develop self-esteem and awareness of the possibilities of social reintegration.

The results of this study should be viewed with some limitations. It was a cross-sectional study and sought inferences with regard to causal factors without, however, establishing a temporal relationship. The self-perception questionnaire may have been influenced by social acceptance and social desirability of their addicted peers.

The results of this study showed that the low quality of life of users of psychoactive substances is related to the high DMFT, low income and use of cocaine/crack. Thus, strategies with a broader approach to promoting oral health for these individuals are necessary in order to assist in the treatment of rehabilitating drug users.