A disposable inhaler for administering medicament by inhalation having an inhalation channel through which a user may inhale, a container for containing a dose of medicament, at least one subsidiary container for containing a subsidiary dose of medicament and respective release means for selectively opening one or both of said container and said subsidiary container such that one or both of said dose and said subsidiary dose may be released into said inhalation channel at the same time so as to provide a variable dose and methods of providing a variable quantity of substance in a channel comprising opening a first container containing the substance and selectively opening a second container containing the substance.