Suboptimal adherence to maintenance therapy contributes to poor asthma control and exacerbations. This study evaluated the effect of different elements of a connected inhaler system (CIS), comprising clip-on inhaler sensors, a patient-facing app, and a healthcare professional (HCP) dashboard, on adherence to asthma maintenance therapy.This was an open-label, parallel-group, 6-month, randomised controlled trial in adults with uncontrolled asthma (Asthma Control Test (ACT) score <20) on fixed-dose inhaled corticosteroid/long-acting beta-agonist maintenance therapy (n=437). All received fluticasone furoate/vilanterol ELLIPTA dry powder maintenance and salbutamol/albuterol metered dose rescue inhalers with a sensor attached to each inhaler. Participants were randomised to one of five CIS study arms (1:1:1:1:1) reflecting the recipient of the data feedback from the sensors: 1) Maintenance use to participants and HCPs (N=87); 2) Maintenance use to participants (N=88); 3) Maintenance and rescue use to participants and HCPs (N=88); 4) Maintenance and rescue use to participants (N=88); 5) No feedback (control) (N=86).For the primary endpoint, observed mean adherence (sd) to maintenance therapy over months 4-6, was 82.2% (16.58) (n=83) in the "maintenance to participants and HCPs" arm and 70.8% (27.30) (n=85) in the control arm and the adjusted LS mean (se) was 80.9% (3.19) and 69.0% (3.19), respectively (study arm difference: 12.0% (95% CI: 5.2%, 18.8%; p<0.001)). Adherence was also significantly greater in the other CIS arms versus control. Mean percentage of rescue medication-free days (months 4-6) was significantly greater in participants receiving data on their rescue use compared with control. ACT scores improved in all study arms with no significant differences between groups.A CIS can improve adherence to maintenance medication and reduce rescue medication use in patients with uncontrolled asthma.