Thank you for this thoughtful question. PrEP and U=U are both important HIV prevention tools, but they mean different things.
PrEP is for someone who is HIV-negative. It is medication taken before a possible HIV exposure to help prevent HIV. PrEP is very effective when taken as prescribed. The evidence is strongest for sexual transmission. PrEP can also help reduce HIV risk for people who inject drugs, especially when there may be sharing of injection drug use equipment. However, we usually do not describe the level of protection as exactly the same as it is for sexual transmission.
The 2025 Canadian PrEP and PEP guideline states that people who inject drugs should be counselled about PrEP and PEP as part of HIV and STBBI prevention, and should be told how these options can be accessed.
U=U means Undetectable = Untransmittable. This applies to a person who is living with HIV and is on HIV treatment. When their viral load stays very low or undetectable, HIV is not passed on through sex. The PHAC factsheet also explains that HIV is not passed on through sex when a person living with HIV, adheres to daily treatment and their viral load remains below 200 copies/ml, with regular monitoring.
