Extracorporeal shockwave lithotripsy is one of the modalities of treatment of renal stones. It´s a machine that breaks the renal stones extracorporeally. Some drugs, like alpha blockers and calcium channel blockers, can improve the success rates of this procedure. Our objective is to study the real effects of two drugs, tamsulosin and nifedipine, compared to placebo, in the elimination of fragments after the extracorporeal shockwave lithotripsy treatment.