Particle size stabilization process

The present invention provides a new process for stabilizing the particle size of micronized glycopyrronium salt (such as glycopyrronium bromide) which yields a micronized product exhibiting improved chemical and polymorphic stability even after prolonged storage. The invention also relates to compositions comprising said stabilized glycopyrronium salt (such as glycopyrronium bromide) and to dry powder inhaler devices and capsules or blisters comprising the stabilized glycopyrronium salt (such as glycopyrronium bromide). The glycopyrronium salt (such as glycopyrronium bromide) or compositions of the invention may be used as a medicament, for instance in the treatment of asthma, chronic obstructive pulmonary disease or cystic fibrosis or related diseases.