OBJECTIVES: Understanding trends of marijuana use in the USA throughout a period of particularly high adoption of marijuana-legalisation, and understanding demographics most at risk of use, is important in evolving healthcare policy and intervention. This study analyses the demographic-specific changes in the prevalence of marijuana use in the USA between 2005 and 2018. DESIGN, SETTING AND PARTICIPANTS: A 14-year retrospective cross-sectional analysis of the National Health and Nutrition Examination Survey database, a publicly available biennially collected national survey, weighted to represent the entire US population. A total of 35 212 adults between 18 and 69 years old participated in the seven-cycles of surveys analysed (2005-2018). PRIMARY OUTCOME MEASURED: Lifetime use, first use before 18 years old, and past-year use of marijuana. RESULTS: The majority of adults reported ever using marijuana. While the overall prevalence of lifetime marijuana use remained stable (p=0.53), past-year use increased significantly between 2005 and 2018 (p<0.001) with highest rate of past-year use among younger age groups (p<0.001), males (p<0.001) and those with income below poverty level (p<0.001). Past-year use was the most common among non-Hispanic blacks, and less common among Hispanic/Mexican populations (p<0.002). Trends in past-year use increased among all age categories, males/females, all ethnicities, those with high school education/above, and those at all income levels (p<0.01 for all). CONCLUSIONS: While lifetime marijuana use remained stable, past-year use significantly increased between 2005 and 2018. While past-year use remained the most common in younger age groups, males, non-Hispanic blacks and those with lower income; increasing trends in past-year use were significant for all age, sex, race and income categories, and for those with high school education/above. With high adoption of marijuana-legalisation laws during this period, our results suggest an associated increase in past-year marijuana use.An accurate understanding of those most at risk can help to inform decisions of healthcare policy-makers and professionals, and facilitate a safe transition of changing marijuana legalisation and use in the USA.