If Flomax is taken with some drugs, the effects of either could be increased, decreased, or altered. Flomax has been known to cause priapism a painful, persistent erection unrelated to sexual activity. Flomax is intended for a once-a-day intake. Tamsulosin is an alpha-blocker drug used to treat an enlargement of the prostate and bladder neck, making it easier to urinate. Flomax as it is an alpha adrenergic blocker can be used for the treatment of male urinary symptoms caused due to enlarged prostate. Tamsulosin relaxes the muscles in the prostate and bladder neck, making it easier to urinate. If you are allergic to Flomax or any of it's constituents you should not take Flomax without your doctor's prescription.