About Tamsulosin Selective Alpha1a Adrenergic Antagonist , For benign prostatic hyperplasia. Mechanism of Action of Tamsulosin Tamsulosin is adrenergic alpha receptor antagonist. It inhibits alpha 1A and alpha 1D subtype receptors. Tamsulosin selectively inhibits alpha 1A receptor in the prostate and leads to relaxation of smooth muscles in the bladder neck and prostate. This will improve urine flow and reduces BPH symptoms. Adrenergic nerves releases adrenalin which produces contraction of muscles. Tamsulosin is selectively inhibit alpha 1A receptor in the prostate and bladder neck and relaxes the muscles and decrease the obstruction to the flow of urine in prostate hypertrophy. Indications for Tamsulosin 1. Benign Prostatic hyperplasia (BPH) Interactions for Tamsulosin Cimetidine: Results in significant decrease in clearance of tamsulosin AUC. Alpha adrenergic blocking agents: Tamsulosin should not be used in combination with other alpha adrenergics.