We examined first (incident) reports of selected adverse experiences associated with medical therapy in men with lower urinary tract symptoms secondary to benign prostatic hyperplasia.We studied the 6 most common adverse experiences, including nonsexual function related experiences (dizziness, orthostatic hypotension and weakness) and sexual function related experiences (impotence, decreased libido and abnormal ejaculation) reported in the MTOPS (Medical Therapy of Prostatic Symptoms) Study. A total of 3,047 men were randomized to placebo, doxazosin, finasteride or combination therapy and followed for a mean duration of 4.5 years. We compared the incidence rates of adverse experiences at year 1 to the rates thereafter.For each assigned treatment group, the incidence rates were significantly higher for all 6 adverse experiences examined at year 1 compared with the rates thereafter. Men assigned to combination therapy experienced the highest rates at year 1 with rates 3.4-fold to 10.6-fold higher than rates after year 1. The incidence rates for orthostatic hypotension and dizziness were significantly higher in the doxazosin and combination therapy groups compared with the placebo group at year 1. The incidence rates of the 3 examined sexual function related adverse experiences were significantly higher in the finasteride and combination therapy groups than in the placebo group at year 1.Rates of the first report of sexual function related and other adverse experiences associated with doxazosin, finasteride and combination therapy were greatest during year 1 of treatment. These patterns should be considered by patients and physicians when treatment for lower urinary tract function is initiated with these drugs.