Uganda records one of the highest levels of alcohol consumption in Africa, yet the consequences of substance abuse for the family as a functioning social unit remain comparatively underexamined relative to its individual health effects. This study examined the influence of substance abuse on family functioning in Kyazanga Town Council, Lwengo District. Adopting a positivist philosophy and a cross-sectional survey design, data were collected through enumerator administration from 278 adult household members selected via multistage sampling from households in the town council. A structured questionnaire measured four substance abuse dimensions, namely frequency and quantity of use, expenditure diversion, intoxication-related behaviour, and duration and chronicity of use, against family functioning assessed through communication, role performance, affective involvement, and behaviour control. Data were analysed using descriptive statistics, Pearson correlation, and multiple regression in SPSS version 26. Findings revealed that frequency and quantity of use recorded the highest mean while duration and chronicity recorded the lowest. All four dimensions correlated significantly and negatively with family functioning, with expenditure diversion strongest (r = −0.706, p < 0.01), followed by intoxication-related behaviour (r = −0.658, p < 0.01), frequency and quantity (r = −0.579, p < 0.01), and duration and chronicity (r = −0.512, p < 0.01). The regression model was significant, F(4, 265) = 68.41, p < 0.001, explaining 50.8 per cent of variance in family functioning, with expenditure diversion (β = −0.331) and intoxication-related behaviour (β = −0.287) the dominant predictors. The findings situate within a literature documenting that alcohol use in Uganda is socially accepted and consequently under-reported (Ssebunnya et al., 2020), that problem drinking is associated with physical intimate partner violence (Tumwesigye et al., 2012), and that adverse childhood experiences predict later heavy consumption (Satinsky et al., 2022), suggesting an intergenerational transmission pathway. The study concludes that the mechanism of family harm is economic and behavioural rather than merely medical, and recommends household-level economic protection, integration of brief intervention into