Use of the agomelatine or N-[2-(7-methoxy-1-naphtyl)ethyl]acetamide (I) or its hydrates, crystalline forms and acid or base additive salts, for obtaining a drug to treat the sleep disorders of the depressed patient. ACTIVITY : Hypnotic; Antidepressant; Cardiovascular-Gen.; Gastrointestinal-Gen; Anorectic. MECHANISM OF ACTION : Melatoninergic receptor system agonist; 5-Hydroxytryptamine receptor antagonist.