INTRODUCTIONLow-level knowledge of problematic substance use during the perinatal period may lead to numerous adverse outcomes. We sought to determine maternal tobacco, alcohol and caffeine consumption during the perinatal period during the COVID-19 pandemic.METHODSThis prospective cohort study recruited women from five Greek maternity hospitals between January and May 2020. Data were collected with a structured questionnaire initially completed by postpartum women during their hospitalization and re-administered via telephone interview in the first, third and sixth month postpartum.RESULTSThe study sample consisted of 283 women. Smoking rates decreased during pregnancy (12.4%) compared to the pre-pregnancy period (32.9%, p<0.001) and during lactation (5.6%) compared to the antenatal period (p<0.001). The smoking rate increased again after breastfeeding cessation (16.9%) compared to the rate during lactation (p<0.001), but remained lower than the pre-pregnancy rate (p=0.008). Only 1.4% of the women reported breastfeeding cessation due to smoking, whereas those who smoked more during pregnancy were more likely to cease breastfeeding (OR=1.24; 95% CI: 1.05–1.48, p=0.012). Regarding alcohol consumption, it was significantly lower during pregnancy (5.7%), lactation (5.5%) and after breastfeeding cessation (5.2%) compared to the pre-pregnancy period (21.9%, p<0.001 for all correlations). Women who consumed alcohol during lactation were less likely to wean (OR=0.21; 95% CI: 0.05–0.83, p=0.027). Caffeine intake decreased during pregnancy compared to preconception period (p<0.001), while in lactating women it remained at low rates until the 3rd month of follow-up. Caffeine consumption at one month postpartum (β=0.09; SE=0.04, p=0.045) was positively associated with longer duration of breastfeeding.CONCLUSIONSTobacco, alcohol and caffeine consumption decreased in the perinatal period compared to the preconception period. The pandemic may have contributed to the downtrend in smoking and alcohol consumption due to COVID-related restrictions and fear of potential illness. Nevertheless, smoking was associated with reduced duration of breastfeeding and breastfeeding cessation.