This study is testing feasibility and acceptability of a theoretically based mobile application (app), UPrEPU, to increase adherence to pre-exposure prophylaxis (PrEP) among men who have sex with men (MSM) to prevent human immunodeficiency virus (HIV).

This study aims to develop an effective mobile application (app), UPrEPU to recognize the factors and decisions that affect PrEP adherence in high-risk populations to improve PrEP adherence. Key components of the app include a sex/PrEP diary using ecological momentary assessment to facilitate accurate data collection; PrEP taking reminder; HIV and sexually transmitted infections (STI) testing information and reminders; HIV and PrEP information and videos; geo-location.

After eligible PrEP candidates agree to participate in the study, we will ask participants to install the app. Then, we will begin to collect their sexual diary and PrEP taking log via ecological momentary assessment. Participants will also complete monthly assessments. The monthly follow-up will test HIV/STI and drug concentration. The participants will be interviewed for difficulties when they use our app and giving feedback on it.

Inclusion criteria:

• Male.
• Aged 20 or above.
• Resides in Taiwan and able to understand, read, and speak Mandarin Chinese.
• Remains HIV negative prior to and during the study period.
• The results of the laboratory tests are eligible to initiate PrEP.
• Currently taking PrEP or willing to initiate PrEP.
• Reports having 4 times or above anal sex with men in the past month.
• Owns an Android or Apple operating system (iOS) smartphone and willing to download the study app.
• Willing to wear the device we provided during the study period.

Exclusion criteria:

• With abnormal kidney function (creatinine clearance rate ≦ 60 mL/minute).
• Currently on medication that might interact with PrEP, such as drugs contain lamivudine in the pre-PrEP assessment.