5-aminolevulinic acid hydrochloride is a highly effective drug in reducing tumor residuals in transurethral resection of the bladder tumors; however, hypotension is a serious side effect that causes clinical problems. To avoid serious side effects, a pharmacist, in consultation with a physician, decided to discontinue the antihypertensive medication, and the effect of this pharmaceutical intervention was examined retrospectively. This study included patients who received 5-aminolevulinic acid hydrochloride at Gifu Municipal Hospital and were instructed to continue receiving their usual antihypertensive medication on the day of surgery. The control group comprised 17 patients before the pharmaceutical intervention, and the intervention group comprised 18 patients after the pharmaceutical intervention. The difference in systolic blood pressure before and after 5-aminolevulinic acid hydrochloride administration was -19.4±22.5 mmHg in the control group and -2.8±16.0 mmHg in the intervention group. The intervention group showed a significantly lower decrease in blood pressure(p=0.019). Intervention to avoid hypotension through the collaboration between physicians and pharmacists may be effective in improving the safety of 5-aminolevulinic acid hydrochloride.