BACKGROUND: Globally, millions of adolescent girls and young women (AGYW) who menstruate have limited access to appropriate and comfortable products to manage their menstruation. Yathu Yathu was a cluster randomised trial (CRT) that estimated the impact of community-based, peer-led sexual and reproductive health (SRH) services on knowledge of HIV status among adolescents and young people aged 15-24 (AYP). Among the services offered through Yathu Yathu were free disposable pads and menstrual cups. This study aimed to investigate whether the availability of free menstrual products through Yathu Yathu increased AGYW's use of an appropriate menstrual product at their last menstruation and explored the characteristics of AGYW who accessed menstrual products through Yathu Yathu. METHODS: Yathu Yathu was conducted between 2019 and 2021 in 20 zones across two urban communities of Lusaka, Zambia. Zones were randomly allocated to the intervention or standard-of-care arm. In intervention zones, a community-based hub, staffed by peers, was established to provide SRH services. In 2019, a census was conducted in all zones; all consenting AYP aged 15-24 were given a Yathu Yathu Prevention Points Card, which allowed AYP to accrue points for accessing services at the hub and health facility (intervention arm), or the health facility only (control arm). Points could be exchanged for rewards, thus acting as an incentive in both arms. We conducted a cross-sectional survey in 2021 to estimate the impact of Yathu Yathu on the primary outcome (knowledge of HIV status) and secondary outcomes. Sampling was stratified by sex and age group; we analysed data from AGYW only to estimate the impact of Yathu Yathu on use of an appropriate menstrual product (disposable or reusable pad, cup, tampon) at last menstruation. We analysed data at zone-level using a two-stage process recommended for CRTs with < 15 clusters/arm. RESULTS: Among 985 AGYW participating in the survey who had experienced menarche, the most commonly used products were disposable pads (88.8%; n = 875/985). At their last menstruation, 93.3% (n = 459/492) of AGYW in the intervention arm used an appropriate menstrual product compared to 85.7% (n = 420/490) in the control arm (adjPR = 1.09 95%CI 1.02, 1.17; p = 0.02). There was no evidence for interaction by age (p = 0.20), but use of appropriate products was higher among adolescents in the intervention arm relative to control (95.5% vs 84.5%, adjPR = 1.14 95%CI 1.04, 1.25; p = 0.006) with no evidence for a difference among young women (91.1% vs 87.0%, adjPR = 1.06 95%CI 0.96, 1.16, p = 0.22). CONCLUSIONS: Delivering community-based peer-led SRH services increased the use of appropriate menstrual products among adolescent girls aged 15-19 at the start of the Yathu Yathu study. With less economic independence, the free provision of appropriate menstrual products is critical for adolescent girls to access materials that allow them to effectively manage their menstruation.