The use of daily PrEP is highly effective if taken every day, less effective if pills are not taken daily. When starting PrEP, it is estimated that a minimum of 7 days of daily dosing is needed to achieve protective concentrations for receptive anal sex, 21 days for vaginal sex.
https://lalgbtcenter.org/health-services/hiv-related-services/prep-hiv-prevention-pill
