It is known that users of psychotropic drugs often have weight gain, adverse effects on bone mineral density and osteoporosis, but the molecular basis for these side effects is poorly understood. The aim of this study is to evaluate the effects in vitro of duloxetine (a serotonin and norepinephrine reuptake inhibitor) and fluoxetine (a selective serotonin reuptake inhibitor) on the physiology of human adult stem cells. Adipose-derived stem cells (ADSCs) were isolated and characterized investigating phenotype morphology, expression and frequency of surface markers. Then, a non-toxic concentration of duloxetine and fluoxetine was selected to treat cells during adipogenic and osteogenic differentiation. Stemness properties and the differentiation potential of drug-treated cells were investigated by the quantification of adipogenic and osteogenic markers gene expression and histological staining. The collected data showed that the administration of a daily non-toxic dose of duloxetine and fluoxetine has not directly influenced ADSCs proliferation and their stemness properties. The treatment with duloxetine or fluoxetine did not lead to morphological alterations during adipogenic or osteogenic commitment. However, treatments with the antidepressant showed a slight difference in adipogenic gene expression timing. Furthermore, duloxetine treatment caused an advance in gene expression of early and late osteogenic markers. Fluoxetine instead caused an increase in expression of osteogenic genes compared to untreated cells. In contrast, in pre-differentiated cells, the daily treatment with duloxetine or fluoxetine did not alter the expression profile of adipogenic and osteogenic differentiation. In conclusion, a non-toxic concentration of duloxetine and fluoxetine does not alter the stemness properties of ADSCs and does not prevent the commitment of pre-differentiated ADSCs in adipocytes or osteocyte. Probably, the weight gain and osteoporotic effects associated with the use of psychotropic drugs could be closely related to the direct action of serotonin.