There is provided four polymorphs of ferric maltol. Form I is prepared by combining ferric citrate with maltol to form ferric maltol polymorph Form I and wherein the process comprises the use of a ferric maltol seed crystal comprising Form I. Form II is prepared by combining ferric citrate with maltol to form ferric maltol polymorph Form II, wherein the process comprises the use of a ferric maltol seed crystal comprising Form I/II polymorph. Form III is prepared by stirring a mixture of Form I and Form II polymorphs in a water/dioxane mixture at 40°C for one hour. Form IV is obtained from 2-chlorobutane and TBME in the mixed solvent cooling crystallisation of a mixture of Form I and Form II polymorphs. Polymorph Form II is the dominant form. Such polymorphs may be useful in the treatment of iron deficiency with or without anaemia, such as iron deficiency anaemia.
