A particulate coformulation, each particle comprising a core of an active substance surrounded by an excipient coating, the particles having a volume mean diameter of 10 .mu.m or less, which on oral administration releases the active substance at a rate such that the time (T.sub.max) taken to attain the maximum active concentration in the bloodstream is one hour or less. The coformulation may be made using a Nektar.TM. SCF particle formation process.