Pharmaco-psychiatry has contributed to the study of mood regulation mechanisms (thymo-regulation). Anti-manic neuroleptics may induce depressions: anti-depressants may cause mood inversion (with artificial "bipolarity"), and lithium has an action upon alternating disorders of the mood. Correlations with the extrapyramidal syndromes are to be noted: parkinsonism going along with depression, and the antiparkinsonian action with the stimulation of mood. The extent of the role played by neuro-hormones, beta-inhibitors, and releasing-factors is still under discussion. The theoretical notion of mood regualtion makes it possible to single out a special type of psycho-stimulation implying manifold applications.