U=U stands for 'undetectable equals untransmittable'. It reflects a well-established scientific consensus: when a person with HIV takes their antiretroviral treatment consistently and the amount of virus in their blood (viral load) becomes undetectable, they cannot transmit HIV to sexual partners.
Reaching and maintaining an undetectable viral load usually takes several months of consistent treatment and requires ongoing adherence and regular monitoring. If treatment is stopped or doses are missed, viral load can rise again and the protection no longer applies.
U=U has transformed how HIV is understood, reducing stigma and showing that effective treatment is also prevention. It is specific to sexual transmission and does not change advice about other STIs. Anyone living with HIV should stay engaged with a licensed doctor for treatment, viral-load monitoring and personalised advice on what U=U means for their relationships.