The aim of this study was to examine the prevalence of past-month cannabis use and lifetime amphetamine use and to determine associated factors among school-going adolescents in Ghana. A prevalence rate of 5.3% and 7.1% were found for past-month cannabis use and lifetime amphetamine use respectively. The high prevalence of past-month cannabis use in this study is lower to the reported rate of 7.2% found among adolescents in 2012  but seems to indicate an increase compared to an earlier study that reported a prevalence rate of 2.6% . The prevalence rate of 5.3% reported in this study is similar to a UNODC report  indicating that adolescent past 30-day cannabis use was also low in Nigeria (4.4%) and Morocco (4.0%). A recent study also reported past 30-day cannabis use prevalence rates of 5.3%, 4.6% and 4.3% for Namibia, Swaziland, and Mauritius respectively . In this study, the prevalence rate for lifetime amphetamine use was 7.1%, which is comparable to what has been reported among school-going adolescents in previous studies within sub-Saharan Africa [4, 9, 23]. The high prevalence rate for lifetime amphetamine use as found in this study is similar to a UNODC report which found a past year amphetamine prevalence rate of 7.6% among students in Ghana . The current trend for cannabis use in the sub-Saharan Africa region is lower than the rates reported in this study.
The results further showed that age and gender were not significantly associated with either past-month cannabis use and lifetime amphetamine use. These results contradict previous studies that have established such associations [5, 8, 13]. Mental health variables such as anxiety, loneliness and suicidality did not predict either past-month cannabis or lifetime amphetamine use. These results contradict previous studies that have established such associations [8,9,10,11].
In this study, parental substance use was found to be associated with lifetime amphetamine use. This means that school-going adolescents who reported parental substance use were more likely to engage in substance use. This result confirms evidence from previous studies [9, 19] which indicate that parental engagement in a behavior is a huge predictor of offspring engaging in the same behaviour. Determining the association between parental substance use and adolescent substance use later in life is not straightforward . This relationship between familial substance use and the likelihood of substance use in adolescence has been discussed through three (3) main pathways. One school of thought argues that family members with substance use problems may serve as behavioural models for young people living in the same household . The second perspective indicates that family members living with problematic substance use may also store drugs and/or alcohol in the house making these substances more readily available to young people . The third pathway is that substance use has a significant genetic component which explains why children of parents who use substances also use substances . In Ghana, parental substance use may serve as a behavioural model which young people living in the same household imitate. Thus, their behaviour may send a message to these adolescents that it is acceptable for them to do the same.
The results further showed that school-related variables such as bullying victimisation and being physically attacked were associated with lifetime amphetamine use. The relationship between being physically attacked and lifetime amphetamine use is exceedingly complex and may be moderated by a host of individual and environmental factors. It is, however, possible that interpersonal level risk factors within the school environment may have played a role in this association, as indicated by previous studies [13, 15]. Additionally, the relationship between bullying victimisation and lifetime amphetamine use, could possibly be due to prior bullying victimisation that may predispose an adolescent to use amphetamine as a maladaptive coping strategy. This finding may also provide some support for the stress coping and self-medication model where recipients of peer victimisation, particularly those with poor coping strategies or self-regulatory processes may use substances as a way to deal with the pains associated with the victimisation experience [27,28,29]. With no anti-bullying policy in place within Ghanaian schools, in addition to the high prevalence of bullying reported among adolescents , this finding is a wake-up call for the Ghana Education Service (GES). The GES should consider these pathways in policy considerations for staff gatekeeping training programmes to address bullying victimisation.
Previous studies have reported that having more friends is protective against substance use [17, 18]. However, the inverse was found in the present study where the odds of cannabis use increased with a higher number of close friends. It has been reported that friendship provides a channel for adolescents to learn new social skills and subsequently experience positive developmental outcomes. However, it is possible that within the context of this study, having several friends led to the development of negative peer risk behaviours including substance use. Plausibly, such negative peer relationships may be associated with heightened health risk behaviours such as cannabis use, and thus underscore the need to emphasize supportive relationships between peers and develop strategies to promote positive peer support.
The findings also reveal that school truancy was a risk factor for both past-month cannabis use and lifetime amphetamine use. Consistent with the results of this study, several studies have established a relationship between school truancy and illicit substance use (i.e. cannabis and amphetamine use) [14,15,16, 19]. The relationship between truancy and substance use may be attributed to the weakened sense of school belonging among school-going adolescents. Schools are key social institutions which play an important role in constraining problem behaviours among adolescents . However, since adolescence is also a time of increasing independence and searching for autonomy , reduced school engagement may also expose young people to health-compromising behaviours including substance use. It should be noted, though, that while truancy was associated with substance use, not all truants use substances .
Furthermore, school-going adolescents who smoked cigarettes were 12.5 and 4.8 times more likely to be past-month cannabis users and lifetime amphetamine users respectively. The presence of clustering of cigarette use with other illicit substance use including cannabis use has been reported in previous studies [8, 14, 34]. These findings underscore the need for the development of poly-drug use interventions among school-going adolescents.
Limitations of the study
This study has some limitations. Firstly, the key outcome variables, amphetamine and cannabis use, were self-reported. Self-report may be confounded by systematic and social desirability biases. Secondly, the majority of the measures used were single item measures which only allows narrow assessment of these variables. Thirdly, results are based on a cross-sectional database, thus limiting our ability to establish causality. Longitudinal studies concerning amphetamine and cannabis use among school-going adolescents are needed. Finally, the study only included adolescents attending school; out of school, 11–18 year-olds were not included. Therefore, findings are not representative of all adolescents in this age group. Despite these limitations, this is one of the first cross-sectional studies to have used nationally representative data to explore the prevalence of cannabis and amphetamine use and their associated factors among school-going adolescents.