Generally, the majority of the psychiatric patients who participated in the study were young. This could be attributed to social factors like unemployment or stressful work, domestic unrest and political factors such as civil wars that predisposed them to psychological trauma. It was also noted that 21.0% of the study participants, the largest age group of whom were 20 to 29 years old, had history of previous exposure to cannabis. This finding is in agreement with a previous study in the United States in which young adults had the highest rate of emergency department visits related to cannabis.12 Peer influence, curiosity, pleasure and the desire for enhanced physical and intellectual performance amongst young adults could explain this scenario.13 Contrary to the cited perception of the benefits of cannabis, there are reports that students who smoke cannabis get lower grades and are more likely to drop out of school than their non-smoking counterparts.14 This could be attributed to the ability of the psychoactive constituents of the plant to cause learning and memory impairment.15 It is also a precursor for inefficiency at work places and in schools. Additionally, several studies have shown that workers who smoke cannabis are more likely than their co-workers to have work-related problems.16 Moreover, it has been reported that the adverse impact of cannabis on memory and learning can last for days or weeks after the acute effects of the drug wear off.16

Adults (30–39 years old) were the second largest group of participants that tested positive for Δ⁹-THC residues. This was probably because of the nature of activities performed by adults that predisposes them to cannabis abuse. Such activities include building, welding, carpentry and long distance driving, all of which are strenuous jobs. Unfortunately, consumption of cannabis by the above age group may not only affect their mental health but also their reproductive health. This is mainly due to the fact that cannabis affects reproductive functions by inducing hormonal imbalance that can affect libido and fertility.17

Amongst the study group, first-time admissions for mental and behavioral disorders were higher (57.0%) than re-admissions (43.0%). This result corroborates with a previous report in rural, South Western Uganda that the total number of new admissions of psychiatric patients increased by approximately four-fold.3 In this study, Δ⁹-THC residues were detected in 17.0% of the psychiatric patients. Of the seventeen, nine were first-time admissions and eight were re-admissions. This figure is slightly higher than 14.23% reported in India.18 The difference in prevalence between the two countries could be attributed to cannabis being widely available in Uganda, weaknesses in legislation concerning cannabis, idleness, poverty and ignorance about the dangers of cannabis abuse. Although the present study could not directly associate cannabis abuse to psychosis, studies have shown that exposure to cannabis increases the risk of psychosis.9–11 However, it is also reported that psychosis may be a risk factor for cannabis use, because individuals who suffer from psychosis begin to self-medicate with cannabis.19 Regardless of whether cannabis abuse is a risk factor for psychosis9–11 or its abuse is a consequence of psychosis,19 there is need for rigorous control measures to prevent abuse of cannabis in Uganda.

This study also revealed that Butabika National Referral Mental Hospital and Arua Regional Referral Hospital do not carry out any laboratory diagnostic tests for screening of patients for cannabis residues. Such tests would help clinicians in making critical decisions on evidence-based psychotherapeutic interventions. Lack of routine cannabis screening services in the two mental health referral hospitals could be attributed to inadequate funding.

In conclusion, this is the first study in Uganda that has demonstrated the presence of cannabis residues in psychiatric patients. This study revealed that previous abuse of cannabis is associated with occurrence of cannabis residues in psychiatric patients. In addition, mental health facilities in Uganda do not have any laboratory diagnostic kits for detection of cannabis residues. This raises concerns on specificity and effectiveness of psychotherapy regimes for mental health patients in Uganda. Alcohol, cocaine, heroin, pethidine, tobacco, khat and kuber were the other substances abused in various combinations. We therefore recommend further studies on the effect of cannabis, as well as the synergistic effects of multiple exposure to psychotropic substances, on psychiatric patients.