One possible side effect of selective serotonin re-uptake inhibitors (SSRI) is the exacerbation of nervous tics in a 12-year-old boy treated with tiapride following prescription of paroxetine for a depressive syndrome. Potential causal factors include residual cholinergic activity of paroxetine, the observably increased drive under paroxetine, metabolic properties, and protein binding. The problem of side effects under selective serotonin re-uptake inhibitors, as well as the issues of co-morbidity and co-medication in the treatment of nervous tics and Tourette's Syndrome are discussed.