Inclusion Criteria:  at least 18 years of age, has a prescription for PrEP received first prescription for PrEP at least one month ago reports taking an average of fewer than 6 PrEP doses per week of over the past month has phone that is compatible with the Carium app.  Exclusion Criteria:  cognitive impairment that would jeopardize informed consent and/or intervention comprehension active psychosis not fluent in English.