Purpose of Review <p>Circadian rhythms regulate sleep–wake cycles and other biological and behavioral processes, and are known to interact bidirectionally with substance use and substance use disorders (SUD). Emerging evidence suggests these interactions being modulated by sex-based biological and psychosocial factors, yet the research from a sex-specific perspective remains limited. This review analyzes and synthesizes the existing evidence on sex-related differences in circadian rhythm among adults with substance use and SUD.</p> Recent Findings <p>Following the PRISMA-ScR framework, we searched seven databases for primary studies published in the last decade reporting circadian parameters (e.g., sleep quality, chronotype) with sex-related outcomes in adults with substance use/SUD. Twenty-three eligible studies were selected, and data were extracted and synthesized narratively. Women consistently exhibited poorer sleep quality, higher insomnia symptoms, and stronger associations between substance use (especially alcohol and cannabis) and circadian disruption. Despite these patterns, most studies treated sex as a secondary variable or predictor, and objective circadian measures (e.g., actigraphy, melatonin) were rarely employed. Circadian differences were also evident, with evening preference linked to greater SUD risk in men, while social jetlag was more strongly associated with alcohol misuse in women.</p> Summary <p>Sex differences are reported in sleep and circadian characteristics among people with substance use/SUD, with women exhibiting greater problems. Current research is mainly considering sex as a secondary variable and there is a lack of sex-stratified data, which might be masking sex-based differences and leading to inaccurate conclusions about efficacy, safety of treatments, or risk factors. A gender-informed approach is essential for advancing in prevention and treatment strategies.</p>