Use of agomelatin or its hydrates, crystalline forms or additive salts of an acid or a base, is claimed for obtaining a drug for treating bipolar disorders. An independent claim is included for an association containing agomelatin and a thymoregulator agent. ACTIVITY : Neuroleptic; Antidepressant; Cardiovascular-Gen.; Hypnotic; Sedative; Anorectic; Eating-Disorders-Gen. In a test, the ability of agomelatin to treat bipolar disorder was tested in human patients. The results showed that 81% of the patients showed positive improvement. MECHANISM OF ACTION : Melatonergic receptor agonist; 5-Hydroxytryptamine 2C receptor antagonist.