The present invention relates to a method for preparing solid pharmaceutical compositions comprising fine particles of at least one active substance, dispersed on and (or) within a divided solid. This method is characterized in that a solution is formed which comprises at least one active substance in a fluid at supercritical pressure, said solution then being expanded in a chamber under temperature and pressure conditions for which a part of said fluid is in the liquid state at the time of the expansion, said fluid thus expanded being brought into contact with a divided solid in said chamber.