The present invention provides co-​crystals of glycopyrronium bromide with lactose. The glycopyrronium bromide and lactose in the novel co-​crystals are present in a stoichiometric ratio of from about 1 :2 to 2: 1. These are characterized by XRD and DSC. Processes for prepg. the novel co-​crystals are also provided. The co-​crystals are also disclosed for use as a medicament, in particular, for treatment of respiratory complaints, such as chronic pulmonary obstructive disease (COPD)​, bronchitis and asthma. Pharmaceutical compns. comprising the co-​crystals as active ingredient are also presented.