This essay is based in a self-reflexive collective process and intends to present the chemsex scene in Lisbon and harm reduction responses implemented to address the needs of chemsex practitioners. The analysis considered professional experiences, participant observation, literature review of the relevant data in Portugal and autoethnographic data from a chemsex practitioner and peer educator. This essay aims to present the community-led creation of a transdisciplinary collaborative network able to assess and respond to chemsex-related risks in Lisbon. Specifically, we aim to: (i) present the chemsex scenes in Lisbon; (ii) discuss the setting up and preliminary results of a collaborative network and harm reduction responses targeting chemsex practitioners. The work implemented in Lisbon demonstrates that chemsex is a global trend with localized idiosyncrasies that must be addressed when designing local tailored interventions. It also reiterated that harm reduction organizations are in a privileged position to detect, monitor and respond to emerging trends at local level. Moreover, the work implemented in Lisbon demonstrated that transdisciplinary collaborative networks, involving communities—chemsex practitioners, gay-friendly and queer venues and collectives—and professionals working in the fields of intersection of chemsex (drugs, sexual health, mental health, gender diversity, gender-based violence), can be effective in the local early detection and response to chemsex-related risks.