The consumption of medicinal plants (MPs) has increased dramatically worldwide. In spite of the fact that they generally have a broad therapeutic range, they are not exempt of side effects and interactions when consumed concomitantly with conventional medication. The objective of this study was to analyze the consumption of medicinal plants by an Uruguayan psychiatric population in order to anticipate their possible interactions with the drugs commonly prescribed in these patients. Interviews of ambulatory patients who acquire their medications from the Pharmacy of Hospital Vilardebó were carried out. Evaluation of possible pharmacokinetic and pharmacodynamic interactions between twelve of the most prescribed conventional medications (quetiapine, lithium, flunitrazepam, sertraline, clonazepam, levomepromazine, haloperidol, valproic acid, olanzapine, fluoxetine, risperidone and clozapine) and the most consumed medicinal plants were studied. Two hundred and fifteen interviews were completed. 66% of the interviewed consumed medicinal plants. Potential interactions between the medication and the most consumed medicinal plants such as Aloysia citriodora (cedrón), Achyrocline satureioides (marcela), Tilia platyphyllos (tilo), Baccharis trimera (carqueja), Mikania laevigata (guaco) and Matricaria chamomilla (manzanilla) were found. A high consumption of medicinal plants was detected among these patients, thus enhancing the prevalence of their interactions with the studied drugs.