The present invention provides a process for the preparation of crystalline Lorcaserin hydrochloride hemihydrate of Formula (la), which comprises, Formula (la) (i) providing a solution of Lorcaserin base in a solvent (ii) if water is present, removing water from the reaction mixture (iii) adding hydrogen chloride to the reaction mixture (iv) combining the reaction mixture with a suitable anti-solvent and (v) isolating the crystalline Lorcaserin hydrochloride hemihydrate of Formula (la).
