Background Effectiveness of HIV postexposure prophylaxis (PEPSE) correlates with speed of uptake following HIV exposure. Time to first dose has not improved in the UK for over 10 years. On-demand pre-exposure prophylaxis (PrEP) has shown that people can self-start medication for HIV prevention. We hypothesised that advanced provision of PEPSE (HOME PEPSE) for men who have sex with men (MSM) to self- initiate would reduce time to first dose following HIV exposure. Methods Phase IV, randomised, prospective, 48-week, open-label study was carried out. MSM at medium risk of acquiring HIV were randomised (1:1) to immediate or deferred standard of care (SOC) HOME PEPSE. Every 12 weeks, participants self-completed mental health/risk behaviour surveys and had HIV/sexually transmitted infection (STI) testing. HOME PEPSE comprised a 5-day pack of emtricitabine/tenofovir disoproxil fumarate/maraviroc 600 mg once daily initiated following potential exposure to HIV. If taken, participants completed a risk survey; PEPSE continuation was physician directed. Primary outcome was time from potential exposure to HIV to first PEPSE dose. Findings 139 participants randomised 1:1; 69 to immediate HOME PEPSE and 70 to deferred HOME PEPSE. Median age 30 years (IQR 26-39), 75% white, 55% UK born and 72% university educated. 31 in HOME PEPSE and 15 in SOC arm initiated PEPSE. Uptake of HOME PEPSE was appropriate in 27/31 cases (87%, 95% CI: 71% to 95%). Median time from exposure to first dose was 7.3 hours (3.0, 20.9) for HOME PEPSE and 28.5 hours (17.3, 34.0) for SOC (p<0.01). HOME PEPSE was well tolerated with no discontinuations. No significant differences in missed opportunities for PEPSE uptake, sexual behaviour or bacterial STI infections between treatment arms. Interpretation HOME PEPSE reduced the time from exposure to first-dose PEPSE by 21+ hours, with no impact on safety. This significantly improves the efficacy of PEPSE and provides an option for people declining PrEP.