A pressurised metered dose inhaler or asthma puffer comprising a canister, wherein the canister contains a formulation comprising a tiotropium salt, and organic acid and an HFA propellant is described. The inhaler has a resilient spring button (460) for applying a preload capable of actuating the internal valve of the canister (40) to release a metered dose of the formulation from the canister. It also includes a resisting mechanism (440. 495, 540) for stopping unwanted discharge of a dose.
