We describe a teaching experience that is based on the ongoing discussion about the legalisation of marijuana, which continues to be a hot topic in Mexico and Latin America. The teaching experience took place in a private teaching institution attended by upper-middle-class students, mainly from families with a conservative political inclination. The analysis of the teaching experience focusses on the types of reflections that were triggered among the students during its implementation, and the role of mathematics in such reflections. The results of the analysis show that some of the discussions that were triggered by this activity went beyond the walls of the classroom, involving students from other school grades or even their families. We think that this contribution may be of interest to mathematics teachers interested in practical activities inspired by the critical mathematics education perspective―particularly those that have been tried out in actual mathematics classrooms.