Method of particle formation

A method for forming particles of a target substance, the method comprising (a) co-introducing into a particle formation vessel, the temperature and pressure in which are controlled, an anti-solvent fluid which is either a supercritical or a near-critical fluid;

• a solution or suspension of the target substance in a first vehicle and a second vehicle which is soluble or substantially soluble in the anti-solvent fluid;
• and (b) using the anti-solvent fluid to disperse the solution or suspension of the target substance and the second vehicle, and to extract the vehicles, substantially simultaneously and substantially immediately on introduction of the fluids into the particle formation vessel, wherein the second vehicle is immiscible with the first vehicle, and wherein contact between the solution or suspension of the target substance and the second vehicle occurs a sufficiently short period of time before their dispersion by the anti-solvent fluid, and with sufficient physical mixing, as to allow only insignificant, if any, phase separation to occur between the two vehicles between their contact with one another and their dispersion.