Dipyrone (metamizole), a powerful drug, is widely used as an analgesic and antipyretic; however, the safety of its use during lactation and the potential impact on the offspring are not well established. This study aimed to determine the effect of maternal dipyrone treatment during lactation on offspring development and emotional behavior and on the dam's maternal behavior. Hence, on postnatal day (PND) 2, drinking water only or drinking water containing dipyrone at doses of 100, 300, and 500 mg/kg/day, were offered to lactating mothers up to PND9. Thereafter, all mice were provided regular drinking water. On PND2, all litters were culled to 8 pups (4 males and 4 females). Maternal behavior was evaluated at PND3, 6, 9, and 12, and at PND7 we evaluated locomotor activity in the open field. Reflex parameters and physical development of offspring were evaluated during lactation. At PND7, analysis of ultrasonic vocalization (USV) was performed. When the animals reached adolescence, we evaluated their performance in the open field, elevated plus maze (EPM), and marble burying. Our data demonstrated that maternal dipyrone treatment during lactation not only altered maternal behavior and the onset of physical and neurodevelopmental landmarks but also had an impact on anxiety-like behavior in offspring. (C) 2017 ISDN. Published by Elsevier Ltd. All rights reserved.