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Introduction Standard therapy for HIV treatment has consisted of two nucleoside analogue reverse transcriptase inhibitors (NRTI) paired with a third agent. Use of two-drug regimens (2DR) has been considered for selected patients in part to avoid toxicities associated with the use of NRTIs. This study aimed to compare the real-world outcomes of integrase inhibitor (INSTI)-based three-drug regimens (3DR) versus 2DR of dolutegravir (DTG) + rilpivirine (RPV) or DTG + lamivudine (3TC). Methods All patients in the Spanish VACH cohort switching to INSTI-based 3DR or a 2DR consisting of DTG + RPV or DTG + 3TC between May 2, 2016 and May 15, 2019 were included. Kaplan-Meier curves and Cox proportional hazard models were used to assess time to/risk of discontinuation due to treatment failure (TF) (defined as virologic failure [VF], immunologic failure, or disease progression) and adverse events (AEs). Three secondary analyses were performed: (1) in restricting the analysis to patients who were virologically suppressed (HIV RNA < 50 copies/mL) at switch; (2) matched analysis (2:1, matched by age, sex, number of previous VFs, and line of regimen), and (3) using VF as the primary endpoint in all patients. Results Overall, 5047 3DR and 617 2DR patients were analyzed. Baseline characteristics differed between groups; 2DR patients were older, more treatment experienced, and more likely to be virologically suppressed at switch. Time to discontinuation due to TF was significantly shorter for 2DR (P = 0.002). The hazard ratio (HR) for discontinuation due to TF on 2DR vs 3DR was 2.33 (P = 0.003). No difference was observed for time to discontinuation (P = 0.908) or risk of discontinuation due to AEs (HR = 0.80; P = 0.488). Results were qualitatively similar in virologically suppressed patients, matched analysis, and for VF. Conclusion In the real world, the risks of discontinuation due to TF and VF were more than two times higher in patients switching to DTG-based 2DR than INSTI-based 3DR, with no difference in discontinuation due to AEs. Plain Language Summary People living with HIV (PLHIV) need lifelong treatment to prevent progression to AIDS. Standard HIV treatments use three different drugs in combination, but these can potentially cause unwanted side effects. Treatments using just two drugs have been developed. These aim to reduce side effects and treat HIV effectively. This study included 5664 participants in Spain who were split into two groups: 5047 participants switched from their old treatment to a three-drug regimen (3DR), and 617 participants switched to a two-drug regimen (2DR). The researchers measured how long it took for the participants to stop taking their treatment because it was not working, or it caused too many side effects. At the end of the study, more than 70% of participants in either group were still taking the same treatment. Of the 30% of participants who stopped treatment because it stopped working, those taking a 2DR stopped sooner than those taking a 3DR. This difference started to appear at about 18 months and got bigger until the study ended, which was 3 years after starting treatment. Participants taking a 2DR were twice as likely to stop treatment because it was not working than those taking a 3DR. There was no difference between the groups for how long it took for participants to stop their treatment because of side effects. These results show that for some PLHIV, the 2DR stopped working sooner than 3DR, without the benefit of fewer side effects.