Background: Tenofovir-based antiretroviral therapy (ART) has become first-line in all major HIV treatment guidelines. Compared with tenofovir disoproxil fumarate (TDF), tenofovir alafenamide (TAF) has a favorable renal and bone safety profile, but concerns about metabolic complications remain.

Objective: To assess weight changes, the development of overweight/obesity, and changes in lipid levels 18 months after replacing TDF with TAF.

Design: Cohort study.

Setting: 5 university hospitals, affiliated hospitals, and private physicians in Switzerland.

Participants: 4375 adults living with HIV who received TDF-containing ART for 6 months or longer.

Measurements: Changes in weight and lipid levels were assessed using mixed-effect models. Differences in proportions of newly overweight/obese participants were calculated using 2-proportions Z tests.

Results: 4375 individuals were included, with follow-up between 1 January 2016 and 31 July 2019. Median age was 50 years (interquartile range, 43 to 56 years), 25.9% were female, and 51.7% had a normal body mass index (BMI); 3484 (79.6%) switched to TAF and 891 (20.4%) continued TDF. After 18 months, switching to TAF was associated with an adjusted mean weight increase of 1.7 kg (95% CI, 1.5 to 2.0 kg), compared with 0.7 kg (CI, 0.4 to 1.0 kg) with the continued use of TDF (between-group difference, 1.1 kg [CI, 0.7 to 1.4 kg]). Among individuals with a normal BMI, 13.8% who switched to TAF became overweight/obese, compared with 8.4% of those continuing TDF (difference, 5.4 percentage points [CI, 2.1 to 8.8 percentage points]). Switching to TAF led to increases in adjusted mean total cholesterol (0.25 mmol/L [9.5 mg/dL]), high-density lipoprotein cholesterol (0.05 mmol/L [1.9 mg/dL]), low-density lipoprotein cholesterol (0.12 mmol/L [4.7 mg/dL]), and triglyceride (0.18 mmol/L [16.1 mg/dL]) levels after 18 months.

Limitation: Short follow-up, small subgroup analyses, and potential residual confounding.

Conclusion: Replacing TDF with TAF is associated with adverse metabolic changes, including weight increase, development of obesity, and worsening serum lipid levels.