BackgroundKhat (Catha edulis) is a plant commonly found in the horn of Africa whose leaves are chewed for their psycho-stimulant effects. Several studies have demonstrated the association between khat use and mental health problems. Nevertheless, evidence is mixed and inconsistent, warranting further review of available studies. This scoping review is aimed at investigating the content and quality of evidence base on the associations between khat use and mental health disorders and suggesting avenues for further research.MethodsWe used a scoping review methodology to map the existing evidence using PubMed, SCOPUS, Embase, and CINAHL databases. Primary studies focusing on the association between any pattern of khat use and any form of mental health disorders are included. The review focused on all age groups, any study design, all geographical locations, and any publication year. The terms used for searching eligible studies include khat, mental disorders, and various alternative terminologies. Narrative review is employed to present findings.Results7,121 articles were found, of which 108 were eligible, conducted across 12 different countries. The majority of the studies was done during the last ten years and the studies mostly employed cross-sectional design. About 10 different categories of mental health disorders have been identified as showing associations with khat use. Despite many contradictory findings between the studies, most of the evidence base suggests that khat use is associated with mental health disorders. Non-specific psychological distress is the most frequently mentioned mental health problem (reported in 26.9% of the studies). Khat use as a predictor variable is mostly assessed using a ‘yes/no’ category, and as a result,dose-dependent effectsof khat use on mental health are not given much consideration.ConclusionAlthough most of the studies associate khat use with mental health disorders, the causal relationships are inconclusive given the cross-sectional design of the studies, and the presence of potential confounders and several forms of biases. Available studies also report contradictory findings. Further studies are recommended using prospective designs, standardized and valid measures of khat use, and focusing on specific types of mental health disorders.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13011-023-00545-y.