If you are diagnosed with urine retention due to a large prostate prior to taking Tamsulosin, from our experience it would be worth asking for repeat flow tests to check if it is working - ask when - perhaps start after 2 or 3 weeks).
If this applies to you do read on! - lengthy post!
My husband was suffering from urine frequency which led to his Prostate Cancer diagnosis.
Following a urinary flow test which showed some retention, he was told by the urologist that he could 'try Tamsulosin', as an alternative to a catheter. Neither was explained in any detail as to risks and benefits.
He chose to try the Tamsulosin and soon began to suffer increasing incontinence - copious at night, and also constipation for which laxido was prescribed. His stomach felt a bit hard which he put down to the constipation and he then got an umbilical hernia so he went to his GP who felt his abdomen and sent him straight to A&E. (4 hours wait -too busy - return next day -long wait- chaotic hellhole experience) He eventually got admitted to a well run ward where he received very good attention. He'd been taking Tamsulosin for several weeks and had seen and spoken to drs and nurses about the incontinence and was advised to keep going with the Tamsulosin.
The urologist there quickly diagnosed serious urine retention which was a surprise to us given the amount of urine he had been passing.
This urologist then told him that 'Tamsulosin would not work for his size prostate' (size determined from previous scans and reports by the first urologist)
This urine retention had caused a severe decline to egfr 25 - down from > 90 in his kidney function test taken only a few weeks previous taking Tamsulosin.
Had he not seen the GP about the hernia it would have become even worse.
He then was given drips and had to have the bladder drained with the decompression risks that brings.
After discharge he needed to use a urinary catheter until his successful Green Light Laser surgery for the enlarged prostate.
After having a catheter the TURP or Laser treatment has to be done within a few months - it was left until the time was running out.
In retrospect it would have been worth paying to get it done sooner.It may be worth finding out if an op is an option to Tamsulosin sooner rather than later, as no drugs are required once it's done though many are happy with the drug.
We had to choose between the TURP and the Laser and received little guidance until we persuaded our new urologist to tell us which would he choose - he said the green laser - usually a day procedure with quicker recovery.
(We had the new urologist because we felt that the one we had first should likely have been aware that Tamsulosin might not work among other reasons).
Our new one, who also performed the op is a good communicator with a very pleasant manner and keeps an eye on my husband with regular checks although now he is under an oncologist as well.
The kidney function improved though not back to previous levels.
we believe that this whole sorry saga would have been avoided if the first urologist, who said my husband could 'try Tamsulosin', had arranged for my husband to come back and test to find out if it's working.
Sorry about the lengthy post - I just hope it might help someone somewhere avoid this overall traumatic experience by being aware of the risks and symptoms of urine retention.