As an update to a foundational publication issued by Health Canada in 2003, a systematic review of data on potential adverse effects of caffeine was conducted according to the IOM standard. Five PECO (population, exposure, comparator, and outcome) questions to address five types of outcomes (acute toxicity, cardiovascular toxicity, bone and calcium effects, behavior, and development and reproduction) in four healthy populations (adults, pregnant women, adolescents, and children) relative to comparators: 400 mg/day for adults [10 g for lethality], 300 mg/day for pregnant women, and 2.5 mg/kg/day for children and adolescents (established by Health Canada) were developed. Data was extracted and risk of bias assessments conducted for the 381 articles meeting inclusion/exclusion criteria. Conclusions were drawn for the body of evidence for each outcome using a weight of evidence approach based on that developed by OHAT with slight modifications. When the total body of evidence was evaluated, and when study quality, indirectness, consistency, risk of bias, level of adversity, and magnitude of response were considered, the evidence generally supported that conclusions reached by Health Canada over a decade prior remain acceptable for healthy individuals (400 mg/day in adults, 300 mg/day for pregnant women, and 2.5 mg/kg-day for children and adolescents) for the outcomes evaluated. The results of this systematic review support a shift in caffeine research to focus on aspects such as characterizing effects in sensitive subpopulations and establishing better quantitative characterization of interindividual variability. This review, being one of the first to apply systematic review methodologies to toxicological assessments, also highlights the need for refined guidance and frameworks unique to the conduct of systematic review (e.g., multi-endpoint reviews) in this field.