The timing and magnitude of antiretroviral therapy-associated weight change attributions are unclear.HIV Outpatient Study participants.We analyzed 2007-2018 records of virally suppressed (VS) persons without integrase inhibitor (INSTI) experience who switched to either INSTI-based or another non-INSTI-based ART, and remained VS. We analyzed BMI changes using linear mixed models, INSTI- and tenofovir alafenamide (TAF) contributions to BMI change by linear mixed models-estimated slopes, and BMI inflection points.Among 736 participants (5316 person-years), 441 (60%) switched to INSTI-based ART; the remainder to non-INSTI-based ART. The mean follow-up was 7.15 years for INSTI recipients and 7.35 years for non-INSTI. Preswitch, INSTI and non-INSTI groups had similar median BMI (26.3 versus 25.9 kg/m 2 , P = 0.41). INSTI regimens included raltegravir (178), elvitegravir (112), and dolutegravir (143). Monthly BMI increases postswitch were greater with INSTI than non-INSTI (0.0525 versus 0.006, P0.001). A BMI inflection point occurred 8 months after switch among INSTI users; slopes were similar regardless of TAF use immediately postswitch. Among INSTI + TAF users, during 8 months postswitch, 87% of BMI slope change was associated with INSTI use, 13% with TAF use; after 8 months, estimated contributions were 27% and 73%, respectively. For non-INSTI+TAF, 84% of BMI gain was TAF-associated consistently postswitch. Persons switching from TDF to TAF had greater BMI increases than others ( P0.001).Among VS persons who switched ART, INSTI and TAF use were independently associated with BMI increases. During 8 months postswitch, BMI changes were greatest and most associated with INSTI use; afterward, gradual BMI gain was largely TAF-associated.
