The basic goal of preclinical animal research is to improve understanding of human disease and treatment. Mandates for sex-inclusive research – both in preclinical animal work and in human clinical trials – have prompted discussions about the ethics and functionality of sex-inclusive research. Authors of peer review research articles and opinion pieces have varying opinions regarding sex-inclusive preclinical animals research. The arguments that support sex inclusion in animal research include: a) sex inclusive research in the preclinical animal model stage saves money further down the road in research, b) new understanding in hormonal variation in both male and female mice undercuts a notion that male mice are simpler research subjects, and c) sex-inclusive research is needed for improved treatment and diagnosis for male and female humans down the road. Arguments against inclusive research include: a) increased research cost and time, and b) sex-inclusive preclinical animal research is not useful, and may be harmful, to the development of personalized medicine. Weighing the different arguments present in the conversation regarding sex inclusive research, sex inclusive research is clearly important and necessary moving forward for cost efficiency, scientific discovery, and movement towards precision medicine.