Background: The innovative breath-actuated mechanism (BAM) within the NEXThaler® controls the dose release in response to pressure drop. The effect of the BAM on the dispersion performance from NEXThaler will be evaluated using in-vivo inhalation profiles. Methods: The dispersion performance of a 100μg/dose of Beclometasone Dipropionate (BDP) formulation was assessed, using in-vivo asthmatic inhalation profiles specific to the NEXThaler . The three profiles differed notably from each other with peak inhalation flow rates of 45, 56 and 100 L min-1. Results: There was a noticeable reduction in dispersion performance when the BAM was removed from the NEXThaler device; 51% ± 3% compared to 37% ± 6% on average across all three profiles. Dose evacuation profiles demonstrate that without the presence of a BAM the dose is released at the same time, near the start of the inhalation, regardless of the inhalation profile (0.27 ± 0.01s). The NEXThaler Control BAM releases the dose only when a pressure drop of approximately 2kPa has been reached. Removal of the BAM causes the dose to be released into a slower airflow velocity, 9-11 L min-1 for the No-BAM device variant and 36-37 L min-1 for the NEXThaler Control. This may mean that larger carrier particles are less likely to impact within the device and could reduce the mass of fine active pharmaceutical ingredient (API) detaching from the carrier particles. Conclusion: Dispersion performance can be improved by moderating the release point of the dose; this is exemplified by the NEXThaler device which includes a BAM.