INTRODUCTION: Standardised packaging on tobacco products was required in Norway July 1, 2018. We report pre-registered analyses of the potential impact on daily smoking and on daily snus use among women and men. METHODS: Interrupted time series (segmented regression) on repeated cross-sectional surveys (2012-2019) from two sources: probability samples (Registry Sample, N = 46,957) and market research samples (Market Research Sample, N = 64,465) of Norwegian adults aged 16-79. Self-reported daily smoking and snus use were regressed on a step change impact variable, controlled for trend and demographics (sex, age, region, and education based on national registers in the Registry Sample, and self-reported in the Market Research Sample). RESULTS: There were tendencies of a decline in smoking (Odds Ratio [OR] = 0.94; 95% confidence interval [CI] = 0.87, 1.02; lower-tail p-value [Plower] = 0.07), and women's snus use (OR = 0.89; CI = 0.77, 1.03; Plower = 0.06), but not men's snus use (OR = 1.01; CI = 0.92, 1.11; Plower = 0.59). Analyses using only the Registry Sample did not detect declines in smoking (OR = 0.99; CI = 0.88, 1.11; Plower = 0.43) or women's snus use (OR = 0.99; CI = 0.80, 1.24]; Plower = 0.48), and indicated no decline in men's snus use (OR = 1.18; CI = 1.03, 1.35; Plower = 0.99). Exploratory analyses suggested potential acceleration of the declining trend in smoking (change in trends, OR = 0.97) and of the increasing trend in men's snus use (OR = 1.03). CONCLUSIONS: The analyses indicate that standardised packaging in Norway did not produce a decline in men's snus use. Results are inconclusive regarding smoking and women's snus use. Exploratory analyses indicated a decrease in smoking and an increase in men's snus use. IMPLICATIONS: We could not confirm or disconfirm whether standardised packaging is an effective tobacco control measure in a Norwegian context. According to our analyses, standardized packaging may have effects on smoking prevalence and women's snus use, but is unlikely to reduce men's snus use. The present results may reflect higher effectiveness of standardised packaging for products with stronger health warnings. As the results varied according to samples and outcomes, the study underlines the importance of pre-registering future analyses on this topic. Future confirmatory research should test models of gradual impact of standardised packaging.