The present invention relates to a method useful for forming products which are useful in a pharmaceutical context and products formed by such a method. The invention is a solvent-free method of forming a metastable polymorph of a pharmaceutical active ingredient the method comprising the steps of: placing an amorphous or crystalline compound into an extruder; providing a source of heat to the extruder to heat the compound to a temperature in the range of from 8 °C below the melting point of the compound to 20 °C below the melting point of the compound; and extruding the compound from the extruder. This method if preferably achieved using screw extrusion whereby temperature and shear induce transformational changes. A twin screw extruder is particularly preferred. Products obtainable via this method and apparatus for the method are also claimed. Exemplified polymorphic forms are obtained using artemisinin chlorpropamide carbamazepine and piracetam.

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