A pharmaceutical formulation of agomelatine for oral use, comprising- agomelatine in the form of agomelatine co-crystals with organic acids and- pharmaceutically acceptable excipients,in which- the agomelatine co-crystals are used in the form of pre-blend of the agomelatine co-crystals with a glidant,- the ratio of the agomelatine co-crystals to the glidant in the pre-blend is lower than or equal to 30 : 1, and- the free-water content in the used pharmaceutically acceptable excipients is lower than or equal to 7% w/w.