We compared our survey with similar studies with regard to response rates and methodological issues of study population, sample size, sampling technique, and type of university students surveyed. The overall response rate was 82% for this survey. This is in line with other response rates which ranged from 58.3% to 98.7% [6–9, 11, 12, 19]. Our final sample size was 500, but analysis was done for only 410 completed questionnaires. In comparison, other studies have analyzed data for sample sizes ranging from 132 to 1,690 students [5–9, 11, 12, 15, 19–22]. We used a quota technique to recruit students proportional to faculty size, academic year, and sex. Five studies have reportedly used random sampling techniques [5, 7, 9, 11, 15, 21, 22]. Two studies used mixed random and nonrandom techniques [19, 20]. One study used a nonrandom technique for recruiting students and one study did not specify the sampling technique employed [6, 12]. Our survey was conducted among students from medical and nonmedical faculties alike. Several studies did not specify the faculty background of students [7, 9, 11, 15, 20–22]. Four studies were conducted on medical or health sciences students [5, 6, 8, 12]. In most studies, the majority of respondents were males [5, 8, 9, 11, 12, 15, 19, 21]. In our survey, there were a majority of female respondents. This is expected as most students at the university are females. Only one other study reported a female majority and in one study the sex distribution was not mentioned [7, 20].

Substances and drugs abused in Sudan are tobacco, alcohol, cannabis, amphetamine, opiates, barbiturates, khat, and tranquilizers [23]. Tobacco is the most abused substance in Sudan and is consumed in three forms of snuff (locally known as tomback), cigarettes, and pipe tobacco. Tomback is prepared from locally grown tobacco leaves which are left to dry and then ground to fine powder. It is then moistened with a solution of calcium bicarbonate in water and the moist tobacco is rubbed repeatedly in the hands into very small moist lumps which can then be placed between the upper lip and teeth or lower lip or under the tongue. It is left in the mouth for about 30–40 minutes till the nicotine is absorbed [23]. It is five times cheaper than cigarettes and it is a common belief that it is less harmful [24]. Studies have claimed or suspected that tomback is associated with risk of cancer of the oral cavity [25, 26]. Alcohol is banned in Sudan on religious grounds and law and is not practiced openly in public. The only forms of alcohol available in Sudan are marissa (native beer) and araki (native liquor). Marissa is home-made, produced from fermentation of dura (grain), has a low alcohol content (3%–6%), and causes intoxication when consumed in large amounts. Araki is produced through primitive methods of distillation of fermented grain, palm dates, or bananas. The liquor produced is adulterated with methanol, aldehydes, and ketones. Sometimes araki is taken with marissa. Cannabis is locally known as bango and is illicitly produced in inaccessible areas or hidden between other crops. The foliage is left to dry, crushed into powder, mixed with honey, and pressed to form a cigar-like head which is wrapped in banana leaves, dura leaves, or thick paper. Opiates are smuggled into Sudan while the source of codeine is unprescribed cough syrup. Amphetamines are also smuggled into Sudan [23].

The overall prevalence of substance use for at least one substance was 31% in this study. The prevalence of at least one substance use ranged from 31.1% to 78% in similar studies [7, 9, 11, 12, 15, 21, 22]. There are three plausible explanations for the low overall prevalence for substance use among the students. First, tobacco in Sudan is consumed commonly as tomback which is not favored by the students and tobacco is not advertised. Instead, the Ministry of Health of Khartoum State is leading the efforts to limit tobacco consumption by increasing awareness of the health risks of tobacco consumption through media outlets to enforce the antitobacco laws and calling for taxes to be raised on tobacco production. Secondly, the second most consumed substance, alcohol, is banned and not sold publicly in stores but can only be obtained from sites that illegally produce them. Thirdly, the questionable quality of illegally produced alcohol deters students from consuming alcohol. In our survey, single substance users constituted 45.7% and multiple substance users 54.3%. Two studies reported that among their students 62.4% and 64% were single substance users and 35.1% were multiple substance users [11, 21]. Polydrug use places students at a greater risk for alcohol-related motor vehicle accidents, property damage, and troubles with the police [6].

The lifetime prevalence of substance use in our study was in line with reported figures in the literature for tobacco or cigarette smoking (6%–42.8%) and alcohol (6.2%–74.6%), cannabis or cannabis derivatives (2%–95%), amphetamines or stimulants (2.1%–67.9%), opiates (1.3%–8.3%), tranquilizers or sedatives (5.9%–27%), cocaine (0%–10.9%), heroin (0.7%), and solvent inhalants (1.2%–10%) [5, 7–9, 11, 12, 15, 20, 21]. The past year prevalence of substance use of tobacco or cigarette smoking and cannabis or cannabis derivatives, cocaine, and opiates was similar to rates reported in other surveys for tobacco or cigarette smoking (4.3%–22%) and cannabis or cannabis derivatives (1.7%–7.6%), cocaine (0%–0.4%), and opiates (0.4%–8.3%); but rates for alcohol, amphetamines or stimulants, tranquilizer or sedatives, and solvent inhalants were less than rates reported in the literature for alcohol (21.6%–74.6%), amphetamines or stimulants (8.7%–26.7%), tranquilizer or sedatives (13.6%), and solvent inhalants (2.6%) [5, 7–9]. With regard to current use of substance use, the rates were comparable to figures reported in the other studies for tobacco or cigarette smoking (1.7%–27.5%) and cannabis or cannabis derivatives (0.6%–4.2%), cocaine (0%–0.4%), and solvent inhalants (1.9%); but the rates were lower than the rates reported for alcohol (9.3%–58%), amphetamines or stimulants (4.2%–33.3%), opiates (6.1%), and tranquilizers or sedatives (5.3%) [5–9, 11, 12, 15].

Tobacco use is the most common reported substance use by students in this survey. In Sudan, there is no official tobacco control policy specifically targeting adolescents [24]. Smoking is prohibited at the university. In our study, students reported using cannabis more frequently than alcohol, although cannabis is more expensive than alcohol. The reasons could be that cannabis is smoked and shared among peers, whereas alcohol drinking is usually not shared between peers. Another reason could be that the students, being students of a private university, have more money to spend on cannabis than alcohol. Alcohol tends to be consumed by lower socioeconomic classes and is legally banned. Cigarette smoking and cannabis have been reported to be commonly used as a stress coping strategy [7, 27]. Students at the university frequently cope with academic pressures. This may also explain why we found a greater proportion of multiple substance users than single substance users in this survey as compared to other studies [11, 21]. Regarding the low reporting of cocaine and heroin, previous studies have reported low rates of illicit drug use and this may be attributed to either underreporting or a lack of availability of these substances, but only cannabis is reported more frequently compared to other illicit drugs [15]. It has been shown that knowledge of the risks and perceived harmfulness of cocaine and heroin have an inverse relationship with substance use [28]. The low rates of illicit substance use may also reflect the difficulty with obtaining illicit drugs as they are costly. It should also not be forgotten that the possession and use of illicit drugs is regarded as a criminal activity and one that will be penalized under the law in Sudan.

The reasons reported for initiation of substance use by students in this survey were akin to some mentioned in the literature. Factors reported in previous studies for initiation of substance abuse have included academic pressure, low grade point average, to increase academic performance, to keep alert while reading, temptation by peer groups, to relax, desire to experiment, the lure of popularity, availability of substances, high social class, poor mental health, perceived adult drug use, to relieve stress, to improve thinking and sharpness of mind, changing social values, to be accepted by others, to be sociable, lack of religiosity, low self-esteem, to remain awake at night, poverty, to get personal pleasure, academic dissatisfaction, to increase pleasure during sex, to remove boredom and tiredness, to feel high mood, failure in love affair, to cope with problems, poor relationship with parents, family disputes, industrialization, urbanization, globalization, cultism, violence, and conflict ridden cultures [5, 7–9, 11, 12, 15, 19, 21, 22, 29]. Students in this survey reported curiosity and pleasure as the main reasons for initiation of substance use. This probably indicates lack of awareness about substance use and therefore there is a need to improve awareness about the circumstances and hazards of substance use.

Many adolescents have limited awareness of the adverse consequences of substance use [7]. Similarly, the adverse effects attributed to substance use as noted by the students were in line with those mentioned in other studies. These consequences include exposing students to legal repercussions, troubles with police, decreased work, decreased academic performance, engaging in unprotected sex, increased risk of contracting HIV and other sexually transmitted diseases, lung disease, heart disease, gastrointestinal disease, depressive illness, addiction, unintentional injuries, physical fights, illegal behavior, intoxication while working, absenteeism, violent crime, theft, loss of money, indiscipline, relationship problems with parents, relationship problems with friends, problems with teachers, loss of friends and break-up of relations, financial hardships, damage to objects, and other psychiatric disorders such as lethargy, hopelessness, and insomnia, excessive absence from school, and dropping out of university [5, 8, 9, 15, 20, 21, 30–32]. The use of cannabis is associated with development of schizophrenia, anxiety, and depression [7]. The most common adverse effects reported by students in our survey are health problems and theft or loss of money or valuables. The reporting of health problems can be explained by the fact that tobacco is the most consumed substance and most students in this survey are of medical background and thus are aware of the effects of tobacco. The reporting of theft and loss of money or valuable items could be explained by the fact that the second most abused substance is cannabis which is costly. Adverse consequences pose a threat to the health, social and economic fabric of families, communities, and nations [22]. With adequate knowledge about the harmful effects of psychoactive substances, students might be deterred from using some substances [7].

With regard to sources of substance use, several studies have indicated that the sources were mostly peers, family members, relatives, local grocery shops, and chemists [9, 15, 19, 21]. However, not all students would report their source of substance use [21]. The sources of substance use reported by students in our sample were similar to those reported in other surveys. The most common source was peers in this survey. It has been suggested that peers might serve as good role models for substance use intervention program [15].

Factors reported in other studies indicate that male sex and living in hostels were associated with substance use [11, 15, 20–22]. On bivariate analysis of our data, the male sex was significantly associated with greater substance use, indicating that more male students are involved in substance use than females. Males are inherently at risk of substance use and the stress which is associated with present day education is believed to be a predisposing factor for addictive behavior [22]. This may also result from the higher social acceptability of substance use among males [20]. Living with family and relatives is significantly associated with less substance use in our survey. Many students at the university live with their families and many students of expatriate parents live with their relatives. This highlights the protective role of family and close relatives from negative peer influences. The importance of peer influence and its association with tobacco, alcohol, and cannabis was reported previously [17, 24].

The study strength is that it involved students from all faculties. The study limitations include using a quota sample and the findings may not be generalized to the whole university study population. However, the results obtained are in line with other studies. We cannot rule out underreporting of substance use as a result of reporting bias, recall bias, and social desirability bias. Another limitation is that after the pretest we did not consider the issues around reliability and validity of responses.

Our study has revealed that substance use is common and varieties of substances have been used in the past or are used currently at the university. Use of more illicit substances is not alarming. The most common reasons for substance use initiation were curiosity, pleasure, and relief of psychological stress. Commonly reported adverse effects were health problems, theft or loss of money or valuable items, and poor academic performance. The prime source of substances was peers. Being male is the most significant factor for substance use.