The most common adverse effects of tamsulosin are anemia (decreased red blood cells), decreased white blood cells, nausea, vomiting, abnormal taste, increased triglycerides, and weakness. Low blood pressure, dizziness or fainting, headache, abdominal pain, weight loss, muscle pain, abnormal ejaculation, upper respiratory tract infections, and rash also may occur. Orthostatic hypotension (low blood pressure when rising from sitting or lying down position), priapism (prolonged erection), and an eye problem called intraoperative floppy iris syndrome (IFIS) have been observed during tamsulosin treatment.

Tamsulosin is used in men to treat the symptoms of an enlarged prostate (benign prostatic hyperplasia-BPH). Tamsulosin is known as an alpha-blocker and works by relaxing muscles in the bladder and prostate. Relaxing these muscles helps to relieve symptoms of BPH such as difficulty in beginning the flow of urine, weak stream, and the need to urinate frequently or urgently (including during the middle of the night).This medication should not be used to treat high blood pressure.